How Hormones Shape Sexual Orientation & Behavior | Dr. Marc Breedlove

Dr. Marc Breedlove, PhD, is a professor of neuroscience at Michigan State University and an expert on how hormones shape brain development and sexual orientation. We discuss how prenatal testosterone impacts whether someone is romantically attracted to men or women later in life, and what correlates of sexual orientation — such as finger-length ratios — tell us about the role of hormones in brain and psychological development. We also discuss why the number of older brothers a male has biases sexual orientation. Throughout, we explain how nature and nurture interact to shape male-female differences, behavior, and romantic partner choice. Thank you to our sponsors AG1: https://drinkag1.com/huberman David: https://davidprotein.com/huberman Rorra: https://rorra.com/huberman Function: https://functionhealth.com/huberman Timestamps (00:00:00) Marc Breedlove (00:03:24) Hormones & Sexual Orientation (00:07:37) Prenatal Testosterone, Finger Ratio, Men & Women Differences (00:14:08) Sponsors: David & Rorra (00:16:46) Finger Ratios, Prenatal Testosterone, Gay & Straight Men/Women (00:23:57) Mice & Sex Differences, Androgens (00:26:54) Brain Differences & Sexual Orientation (00:33:52) Group vs Individual Differences, Height Analogy; Bisexuality (00:36:57) Brain Development, Hormones & Behavior; Brain Plasticity (00:42:52) Sponsor: AG1 (00:44:16) Sexual Behavior, Libido (00:51:37) Gay Rams, Brain Differences (00:58:00) Aversion Pathway, Men vs Women, Same-Sex Partner (01:06:58) Congenital Adrenal Hyperplasia (CAH), Intersex Phenotypes (01:13:55) Androgen Insensitivity Syndrome (AIS) (01:18:14) Sponsor: Function (01:19:25) Gay Men & Older Brothers, Maternal Immunization Hypothesis (01:32:55) CAH Carriers, Advantage, Stress Tolerance (01:35:41) Birds & Sexual Differentiation, Gynandromorphs (01:41:32) Anabolic Steroids, Hypersexuality; Adult Brain Plasticity (01:45:31) Age & Testosterone Decline; Sexual Orientation & Activities (01:53:14) Marc's Academic Journey, Ozarks, Luck (02:02:35) Exploration; Kids & Sex Differences (02:08:47) Zero-Cost Support, YouTube, Spotify & Apple Follow, Reviews & Feedback, Sponsors, Protocols Book, Social Media, Neural Network Newsletter Disclaimer & Disclosures Learn more about your ad choices. Visit megaphone.fm/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Andrew D. Huberman?

  The larger the number of older brothers that a male has, the higher the probability that he is gay.

• 0:07Speaker 01

  It's been seen over and over. I mean, it's really one of the rock solid findings in human sexuality. So the way to emphasize the difference is if a baby boy is born today, if he has no older brothers, his odds of being gay when he grows up is about 2%, right? Pretty low. But if he had one older brother, his odds go up by a third. Okay, 2.6. And if he has two older brothers, they go up a third again. All right? Now we're at 3.5. It turns out you've got to have like a dozen older brothers just to have a 50/50 chance.

• 0:43Andrew D. Huberman?

  Welcome to the Huberman Lab Podcast, where we discuss science and science-based tools for everyday life. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. My guest today is Dr. Mark Breedlove. Dr. Mark Breedlove is a professor of neuroscience at Michigan State University, and he is an expert in how hormones shape the developing brain, in particular, how they influence sexual orientation. As you'll learn today, the amount of testosterone that a fetus is exposed to while in the mother has a profound impact, not only on the ratio of finger lengths—yes, you heard that right— but it also plays a meaningful role in sexual orientation.

• 1:26Andrew D. Huberman?

  And in fact, there's a correlation there between finger length ratios and sexual orientation. Now, as wild as that may seem, that result has now been confirmed many times over in humans and in animals. And today, you'll understand why. You'll also learn that every time a woman is pregnant with a male, there's a biological trace of that which biases the likelihood that her next male offspring will be either heterosexual or homosexual. Now, I know this sounds really out there, but these are extremely solid biological findings for which the mechanisms are now understood for both animals and humans. It turns out that the hormones we are exposed to while we are in the womb shape not only the preference for whether somebody is attracted to males or females, but also an aversion

• 2:09Andrew D. Huberman?

  to the opposite, meaning there appears to be the formation of circuits for being attracted to one sex and not attracted to the other. Today, you'll also learn how hormones impact the amount of rough and tumble or social play that kids engage in, the interplay between nature and nurture in shaping male versus female differences, and sexual orientation.

• 2:28Andrew D. Huberman?

  Dr. Breedlove is one of the longstanding pioneers in this field of how hormones shape brain development and psychology. We approach these questions through the lens of biology and statistics. So today's is not a political discussion. Instead, it's a discussion about what is known and what is still not known about this profound aspect of our species. Oh, and we also talk about gay rams. Yes, that's a real thing, and it has important implications for everything we've mentioned thus far. By the end of today's episode, you'll surely think differently about the relationship between hormones and brain development, nature and nurture, and romantic partner choice. Before we begin, I'd like to emphasize that this podcast is separate from my teaching and research roles at Stanford. It is, however, part of my desire and effort to bring zero cost to consumer

• 3:13Andrew D. Huberman?

  information about science and science-related tools to the general public. In keeping with that theme, today's episode does include sponsors. And now for my discussion with Dr. Mark Breedlove. Dr. Mark Breedlove, welcome.

• 3:26Speaker 01

  Thank you. I'm delighted to be here. Very exciting.

• 3:29Andrew D. Huberman?

  Been 25 years since we stood in the same physical space.

• 3:32Speaker 01

  I know. How can that, how can that be possible? I feel like, you know, just saw you a few days ago, but then...

• 3:38Andrew D. Huberman?

  Well, you look great. You look the same, so we can talk longevity protocols at the end, but...

• 3:43Speaker 01

  I'm trying to have a blonde look in my hair, apparently, so...

• 3:45Andrew D. Huberman?

  Well, I've wanted to have you on this podcast since I launched it because you work on one of the most interesting things in the world, which is how and why people become who they are, and how hormones play a role there, how genes play a role there. If you're willing, I'd like to jump from the high dive to the deep end first, right off.

• 4:06Speaker 01

  All right.

• 4:07Andrew D. Huberman?

  Let's talk about this finger-length ratios, sexual orientation study that you published, and somehow I landed on that paper. That's not why I want to talk about it. I want to talk about it because it's an incredibly interesting set of findings. Other people have... Done the same-ish experiments. And there's a whole context there about how hormones influence sexual orientation, independent of behavior.

• 4:31Speaker 01

  We need to step back a little bit for the context. One thing that your listeners might not know is, you know, in the year 2000, there was still a lot of people who regarded same-sex orientation as a choice, a lifestyle choice. That was the political combination of words that meant you could disapprove of people because they were attracted to the same sex. Of course, I'm at Berkeley. I didn't have any truck with such notions at all. And I've always been convinced that sexual orientation is not a choice. And there's an exercise they do in class where I ask, so I'm going to put you to it. So remember the first time you had a crush, right? It might have been someone on TV, it might have been someone at a playground, et cetera.

• 5:16Speaker 01

  So think about it, and I want you to tell me about how old you were at the time in a moment. My guess is it was before puberty.

• 5:23Andrew D. Huberman?

  Yeah, I was six.

• 5:24Speaker 01

  Yeah.

• 5:25Andrew D. Huberman?

  And I hit puberty somewhere, starting around 14.

• 5:28Speaker 01

  So it had nothing to do with puberty, right? It was this thing that happened. And I'll share my experience. So I'm about six or seven. I couldn't have been more than seven. And Marilyn Monroe is on TV, I'm dating myself. And there's a close-up, you know, with that face and the mole, et cetera. And afterwards, I'm just so agitated. I don't, you know, I don't, and I know nothing about sex. I remember I had a hard time going to sleep. So it was like, something about this was really agitating me. And I didn't choose to have that reaction. And my guess is that whatever sex you had your first crush on, that's the one you're going to be attracted to the rest of your life.

• 6:10Andrew D. Huberman?

  Yeah, it's been constant.

• 6:11Speaker 01

  Yeah. Well, so this idea that it was a choice, that always just seemed so absurd to me. On the other hand, even though, you know, I've been doing animal research with giving hormones early in life and seeing what it did to the nervous system, et cetera. And every time I wrote an NIH grant, I've said, "Well, you know, the effect of early hormones may be important for human behavior," but to tell you the truth, I never actually believed that, right? It was just, I just wanted to justify it because it seemed to me that we are so sensitive to social influences. And we have this long stretch of time where, you know, our brains are still growing at a fetal rate of growth until like nine or 10 years of age.

• 6:56Speaker 01

  And we're taking in so much information. And think of what a heterosexual world is, right? About all those Disney movies with Prince Charming and et cetera. And so it always seemed to me that, that social learning would be more than enough to explain why 95% of people are straight. But that doesn't mean that was a choice, and it doesn't mean that they would even be aware of what the social influence was. So my example is, I speak English, you know, I'm hopelessly monolingual, only language I speak. Well, I don't remember learning English, and I certainly didn't choose to learn English, but I'm sure that it's English because of social influences, right?

• 7:36Speaker 01

  So that was where I stood on the question of sexual orientation until 1998, 1999, when this fellow at University of Texas, Dennis McFadden, came out with a paper where it really made me think that prenatal testosterone might have an effect after all, despite my expectations. And this was looking at autoacoustic emissions. Do you want to talk about those?

• 8:04Andrew D. Huberman?

  Yeah, these are people's ears making noise.

• 8:07Speaker 01

  Yeah, I mean, right now, in this studio, if I, if I shut up for a moment, your ears will continue to make little popping sounds that you're not aware of because, having grown up with it, the brain stopped you from perceiving those long ago. Well, but if Dennis puts you in a soundproof room and puts a very sensitive microphone in your ear, he'll, he'll hear these pops. And, and I won't get into the acoustics of why that's a good thing, right? It helps you to focus on the sounds you want to hear. But what Dennis knew is there's a sex difference in how many of these autoacoustic emissions are being made. Girls make more and it's present at birth.

• 8:50Speaker 01

  So Dennis comes out with a strange study. I mean, who would do such a thing? Where he proposes, well, since the sex difference is present at birth, it might reflect prenatal testosterone. And so he measured the autoacoustic emissions in straight men and gay men and straight women and lesbians. And he reports that compared to straight women, the lesbians have fewer of these autoacoustic emissions than straight women. It's like, well, what? What? How would that happen? I couldn't think of any way to explain that except that, well, the lesbian might have been exposed to more prenatal testosterone

• 9:33Speaker 01

  than straight women before birth. And I don't know how to explain that except to say, well, maybe prenatal testosterone, maybe if you're exposed to that before birth, you're more likely to be attracted to women when you grow up. Which, oh, well, that might explain why 95% of men are attracted to women, right? Because they're all exposed to prenatal testosterone. So this oddball study really gets me to thinking that maybe there's, you know, something to that. But I'll forget it. You know, I'm still working with my rats and paramiscus and Siberian hamsters and stuff. I'm happily doing that. And then, and I remember it so well. And I, in 1999, I'm in my office at Berkeley and I read this paper that says there's a sex difference

• 10:16Speaker 01

  in the ratio of fingers that's present in nine-year-old children. What? I've studied sex differences my whole adult life. How do I not know about this? And it turns out that if you, if you measure the length of the second digit,

• 10:34Andrew D. Huberman?

  The pointer finger.

• 10:35Speaker 01

  The pointer finger.

• 10:36Andrew D. Huberman?

  For those just listening, yeah.

• 10:37Speaker 01

  Right. And the length of the ring finger. And you can, you can do a simple ratio. Divide the length of the second digit by the fourth digit, so-called 2D, 4D ratio. And a guy named John Manning was reporting that there's a sex difference there, that it's, that that ratio tends to be smaller in men than in women and that it's present in children. It's like, well. Wait a minute, a sex difference in the body that's present before puberty, I know enough about sexual differentiation of the body, it's almost certainly due to prenatal testosterone.

• 11:11Andrew D. Huberman?

  Forgive me for interrupting you, but people are probably looking at their hands right now.

• 11:14Speaker 01

  Oh, yes.

• 11:14Andrew D. Huberman?

  And I just want to point out that these are averages.

• 11:17Speaker 01

  Yes.

• 11:18Andrew D. Huberman?

  But it's, I think the 2D, 4D thing, for people that aren't familiar, even though you explained it quite clearly, can be a little confusing. Basically, in men, the finger lengths are more different than they are in women, and there are some differences in in that statement according to sexual orientation that we'll get into. But when you say, in other words, the typical heterosexual male pattern is that the pointer finger, right, is shorter than the ring finger.

• 11:45Speaker 01

  Right, right.

• 11:46Andrew D. Huberman?

  Whereas in women, they tend to be more similar. Again, these are averages, and not to give it away, but this is because people are looking at their fingers right now.

• 11:55Speaker 01

  Yes, yeah, and let me just say, don't panic.

• 11:58Andrew D. Huberman?

  Yeah, right.

• 11:59Speaker 01

  We're gonna, we're gonna walk you through this, you're gonna be fine.

• 12:01Andrew D. Huberman?

  And the difference between men and women is more pronounced on the right hand, as I recall.

• 12:07Speaker 01

  That, that's true too.

• 12:08Andrew D. Huberman?

  Did I earn my authorship on the paper?

• 12:10Speaker 01

  Well, that and the, and the fact that you persuaded so many people to answer our weird questions and let us see rocks their hands.

• 12:16Andrew D. Huberman?

  Okay, so please continue, but I know that the moment that came out, you know, hopefully there were no car accidents if people were driving, but, but, uh, these are averages, but that's the pattern that was observed.

• 12:26Speaker 01

  That's the pattern we thought, well, I'd never worked with humans before, but I'm sitting in the Bay Area. We have loads of gay people around, and you, you know, so it's like, well, let's, I guess we could try to do this. And so we started going out to street fairs, you were, you were with us, going out to street fairs and giving people, asking people questions, asking them to fill out a questionnaire anonymously, and, um, and I remember it, it was one of the organizers of one of the street fair, but I said, well, what should we do as an incentive to get people in? And they said, well, offer them- Scratch your tickets. Lottery tickets. Lottery tickets. So, so we, we ask people, will you please answer these very personal questions about,

• 13:10Speaker 01

  about who you have sex with, who you want to have sex with, et cetera, and tell us everything about yourself anonymously, and we'll give you a $1 lottery scratcher people ticket. And people will do anything for a $1 lottery scratcher ticket. I mean, it was just a bit, which is weird because you do the math and they're worth like 27 cents, right? But, but, but people want them. And, oh, and by the way, can we Xerox your hands? And the last two questions we asked about handedness, but it was really just to keep them from panicking. So, you know, and it, by the way, it was, it was the least expensive experiment I'd ever done in my life because really, you know, compared to, to any experiment with

• 13:53Speaker 01

  a rat where step one, buy a rat for 20 bucks, right? So it's, so, and it was an odd experience going in the 7-Eleven that morning and saying, please, I'd like 750 $1 lottery scratcher tickets.

• 14:08Andrew D. Huberman?

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• 14:53Andrew D. Huberman?

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• 15:38Andrew D. Huberman?

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• 16:19Andrew D. Huberman?

  and disinfection byproducts, while preserving beneficial minerals like magnesium and calcium. It requires no installation or plumbing. It's built from medical-grade stainless steel, and its sleek design fits beautifully on your countertop. In fact, I consider it a welcome addition to my kitchen. It looks great, and the water is delicious. If you'd like to try Rora, you can go to rorra.com/huberman and get an exclusive discount. Again, that's Rora, R-O-R-R-A dot com slash huberman. Well, as long as we're getting into the context, it's interesting because you said there are a lot of gay people in the Bay Area. But it was very clear, as I recall when doing the study, that if we wanted to get a large sample population of gay men, we would need to go to the Castro District in San Francisco.

• 17:04Speaker 01

  Yeah, as we did.

• 17:04Andrew D. Huberman?

  And if we needed to get a large cohort of gay women, we need to go to the Solano Street Fair in Berkeley.

• 17:09Speaker 01

  And in Oakland. So there was a brand-new Oakland gay festival that got started. And yeah, Oakland is a wonderful place to find lesbians. So what are the charms of the place? I thought the whole idea was kind of crazy, actually. I mean, I didn't think we'd come up with anything. And I insisted on measuring all the digits myself, which I did twice. Boring as hell.

• 17:35Andrew D. Huberman?

  I recall when we were on, what was it, like, third floor of Tolman Hall? And you came running in.

• 17:42Andrew D. Huberman?

  I was talking to my advisor, our good friend Irv Zucker, one of the pioneers of circadian biology, discovered the suprachiasmatic nucleus with Bob Moore and others, but, and you came running in with, with, with a ruler and you said, "Give me your hands." And you grabbed my hands and you measured them and you go, "Well, that's weird because it's like, different on one hand than the other." And then you go, "Okay." And you took the notes and you measured his hands and he left. And I thought, "What in the world is he doing?" It turns out that was the early origins of the study.

• 18:10Speaker 01

  Yeah, yeah. No, no. And anyway, so, so I measured these hands and, and I'm doing the, the, the math at the end of the day. And low and behold, I mean, I don't, I don't see any difference in the digit ratios of gay and straight men, right? Okay.

• 18:26Andrew D. Huberman?

  Between gay and straight men.

• 18:27Speaker 01

  Yeah, yeah. I didn't see any difference there.

• 18:28Andrew D. Huberman?

  Which itself is interesting.

• 18:29Speaker 01

  Absolutely.

• 18:30Andrew D. Huberman?

  Because it implies more or less equivalent amounts of prenatal testosterone exposure.

• 18:35Speaker 01

  Which I think is the case, yes.

• 18:37Andrew D. Huberman?

  And, and right now, just forgive me, but, you know, my, some people might say, "Well, that's not surprising." But in the eighties and nineties, the Hollywood stereotype of gay men was that they were all very effeminate.

• 18:50Speaker 01

  Yep.

• 18:51Andrew D. Huberman?

  Um, since then, there's been an evolution. In fact, I haven't seen it, but many people I know are very excited about this recent show about these two gay hockey players.

• 18:58Speaker 01

  Yes, yeah.

• 18:59Andrew D. Huberman?

  So the whole context is these guys that are very masculine but are gay, right? So for people hearing this that are younger than 40, they're going to think, "Well, duh."

• 19:08Speaker 01

  Yeah.

• 19:09Andrew D. Huberman?

  But for people that grew up in my generation or your generation, it was a bit of a shocker to a lot of people, um, because depending on their level of exposure to the gay community, they may or may not have realized that not all gay men are, uh, effeminate.

• 19:24Speaker 01

  Exactly. No, and, and you know, that idea that gay men might have been under-androgenized, there was always a part of it that was... That always seems strange to me. So the big sex differences in human behavior are not in, you know, math skills and the verbal skill. Those are tiny, right? The really big sex differences in human behavior are in sexual attitudes. And the biggest sex difference is one sex is much more interested in multiple partners and younger partners than the other, right? Everyone knows which sex that is. One sex is much more interested in casual sex than the other. Everyone knows that. One sex is much more interested in visual pornography than the other sex.

• 20:06Speaker 01

  Those are huge sex differences compared to any, you know, cognitive things. And in all those ways, gay men are totally masculine. So how would that work? That, that, you know, they were under-androgenized and yet they have all these sex differences in sexual attitude. I, I think the difference between gay and straight men isn't in how much prenatal testosterone they got. I think it's in how their brains responded to the testosterone that they got. And we can talk about that some more later. But back to the digit ratios, the lesbians had more masculine digit ratios than the straight women, on average. And, and as you said, that's been replicated by many different labs.

• 20:48Speaker 01

  Dave Putz at Penn State and, and Ashlyn Swift Galant and I recently published like the third meta-analysis and it's clear so many people have seen it. It's there. And, and as with Dennis's autoacoustic emissions, I don't know how to explain that. Why, why would lesbians have a more masculine digit ratio than straight women unless, on average, they were exposed to more prenatal testosterone than straight women? And why would that matter unless being exposed to prenatal testosterone makes you more inclined to be attracted to women when you grow up? And what's really weird about, think about the time wag.

• 21:30Speaker 01

  Your first crush, this sudden, this mysterious, for me, it was like a visitation, right? It's like, where'd this come from? That happened six years after you were out of the womb, right? And so it's really strange to think that something that happened to you before you were born. Would have an influence on who you're going to be attracted to six, 10 years later when you have your first crush. So it was, and I can tell you that when we published that in 2000, it did cause quite an uproar. I heard from a lot of strangers that I'd never heard from before, and it was pretty interesting.

• 22:13Speaker 01

  Of course, there were several people wrote who hadn't told me that they were gay, and they were very positive, very supportive. But I got lots of emails from people saying, "I know you're lying. You're making this up to justify your gay lifestyle." You know, it's like, "Well, okay, except I don't happen to be gay." I mean, we had a nice mix of orientations on the research team, but people were having a hard time with it. And to assure your listeners about if they were looking at their hands, if they're a woman and they looked at the hands and they see that the index finger is quite a bit shorter than the ring finger, and they're thinking, "I thought I was straight," etc.

• 22:54Speaker 01

  So here's a joke that I tell, which is, if you want, I'm going to teach you right now. You gather a big sample of people, and I'm going to teach you how to look at their hands, look at the right hand, and guess their sexual orientation, and you're going to be right 95% of the time. Okay? You want to learn how? So look at the right hand, pay really careful attention to whether the index finger is shorter than the ring finger, and no matter what, you see, guess, "Straight." And you will be right 95% of the time, if it was a random sample of people. So the important thing to get across is that while these average differences across group

• 23:34Speaker 01

  are theoretically important, because they do indeed indicate that lesbians are more likely to have been exposed to slightly more testosterone before birth, that doesn't mean you can predict how much testosterone one person was exposed to from their situation, because other things influence the situation.

• 23:51Andrew D. Huberman?

  Fascinating study.

• 23:53Speaker 01

  I got made fun of quite a lot, but you know, I thought it was a blast.

• 23:57Andrew D. Huberman?

  I mean, some of the more outrageous things that people have asked me about the study over the years were, and by the way, they all came from men, were if I cut off my index finger, you know, will that raise my testosterone? Someone actually asked that.

• 24:14Speaker 01

  Yep.

• 24:15Andrew D. Huberman?

  No, it's not reverse causality.

• 24:16Speaker 01

  I would have said, "Well, let's try it and see."

• 24:19Andrew D. Huberman?

  Again, now, most people, I realize there are differences across the country and the world on this stance, but I think most people would say, yeah, like, okay, there's a biological variable associated with sexual orientation. The fact that it's linked to prenatal testosterone is very interesting. And the question that then comes up is, is there anything about behaviors associated with gay or straight men, gay or straight women, that change hormone levels, independent of all this, right? Because, put differently, I think for a number of years, people were interested in whether or not gay men, as you pointed out, would have higher or lower levels of testosterone. The hypothesis was lower, based on the effeminate

• 25:03Andrew D. Huberman?

  stereotype. Turned out, probably the opposite outcome.

• 25:07Speaker 01

  If anything, right.

• 25:08Andrew D. Huberman?

  Yeah. Anyone that went to gyms in the 1980s and 90s would also realize that the low androgen argument was wrong, although steroids become a problem in gyms too, but, you know, it gets confounded. But, am I correct in remembering that this effect is also present in frogs, or mice?

• 25:29Speaker 01

  The sex difference is present in mice.

• 25:31Andrew D. Huberman?

  That's D2/D4 ratio difference?

• 25:32Speaker 01

  Yes.

• 25:33Andrew D. Huberman?

  I find that amazing.

• 25:34Speaker 01

  Well, I did too. So Wendy Brown and I did that first, and, you know, I'd worked with mice and rats all my life, but, you know, I'd never noticed that this is, that the first digit is the shortest, and that the third digit is the longest, and that sometimes the second digit is longer. You know, it's like, I mean, it's, you know, evolution's real, right? It happened. And so, yeah, there's a sex difference there. And a group looked at mice and did lots of genetic manipulations, and it turns out that if you make the androgen receptor dysfunctional, the sex difference goes away. And they showed,

• 26:15Speaker 01

  that in mice at least, there's more androgen receptor in the growing bones of the fourth digit than the second digit. And then they showed that, that that's why the fourth digit grows a little bit more than the second digit.

• 26:28Andrew D. Huberman?

  Beautiful. So, and I should have said this earlier, androgens are things like testosterone, DHT, other androgens. Men and women both have them, other animals have them. Incredible. So, let's talk about...

• 26:44Andrew D. Huberman?

  Effects of testosterone when we're in the womb.

• 26:47Speaker 01

  Yeah.

• 26:48Andrew D. Huberman?

  Obviously, it's having an organizing effect on the body plan, this D4-D2 ratio.

• 26:53Speaker 01

  Right.

• 26:54Andrew D. Huberman?

  What about in the brain? What is known about brain differences between men and women that identify as straight or gay?

• 27:04Speaker 01

  Well, in terms of prenatally, we don't know, but the very famous study from Simon Levey, who was already a highly respected neuroscientist, lots of wonderful papers in development of the visual system. Simon Levey got everyone's attention well before we did when he looked at a brain region in the hypothalamus, a specific region called the preoptic area, or POA, and he looked there and compared the size of the POA in the brains of gay men versus straight men. And he looked in the preoptic area because in rats, there's a very prominent sexual difference, or sex dimorphism, in a nucleus in the rat brain in the preoptic

• 27:48Speaker 01

  area. And the nucleus got named the sexually dimorphic nucleus of the preoptic area, the SDN POA. And Simon knew there was a huge sex difference there in rats, and so he looked at the brains of gay and straight men and found a nucleus there that may or may not be the same as the SDN POA, but is larger in men than in women. And what he found was that the nucleus in gay men was smaller than in straight men, and in fact, not significantly different from the size of the nucleus in women.

• 28:21Andrew D. Huberman?

  So it wasn't hyper male, like the finger length ratio was?

• 28:25Speaker 01

  No, no, no. In that case, it indicated less, either less androgen exposure, or less of a response to the androgen that was there. And Simon got even more of an uproar than I did. Published his paper in Science and there were lots of people that were very skeptical, including some neuroscientists, but eventually another group replicated it.

• 28:50Andrew D. Huberman?

  That's what I was gonna ask because I recall that the two major critiques of the paper, one was fair in my opinion. It was that some of the postmortem samples were from people who had died of AIDS and so AIDS has some known neurodegenerative effects

• 29:04Speaker 01

  Yep.

• 29:05Andrew D. Huberman?

  that may or may not have impacted the samples, although hopefully they control for that. And then as I recall, he also got some pushback because he is openly gay and people accused him of gen- uh, agenda'd. I didn't say gendered, I said agenda'd

• 29:20Speaker 01

  Yep.

• 29:21Andrew D. Huberman?

  Science.

• 29:21Speaker 01

  Yep. Yeah, that he was part of some conspiracy, a gay agenda to force Americans to regard people with same-sex orientation as somehow okay.

• 29:32Andrew D. Huberman?

  But a replication of the study from an independent group that presumably has no reason to be biased whatsoever.

• 29:39Speaker 01

  They were very skeptical of it. So that was William Breyer who eventually, and there's an interesting aspect of it. It took him a long time to get a sample big enough because, you know, Simon, it was such a horrible time in AIDS epidemic. There were so many young men dying that Simon had no trouble finding enough brains to do the sample. And then as treatment got better, the death rates of HIV started going down. And so it took longer for William Breyer to gather the samples, but he eventually did. And even though he was skeptical of it, he saw it too. The question about AIDS, I mean, Simon was able to address

• 30:23Speaker 01

  that in that he also had some straight men who had AIDS and he didn't, you know, they didn't, they weren't significantly different from other straight men. But, but, and so it was widely interpreted as proof that sexual orientation is not a choice, that it's something that happens to you. And of course, I don't think sexual orientation is a choice, that's true, but Simon himself made it clear. That he could only look at this nucleus in adults, right? You can only look, it's so tiny. The sexually dimorphic nucleus, the preoptic area in humans, it's about the size of a grain of sand, right? So you gotta have a microscope and you can only, there's no non-invasive way to look at it.

• 31:06Speaker 01

  And he pointed out that he didn't know if, what the order of causation was. He didn't know if those men had been born with a smaller SDNPOA and that's why they became gay. Or did something else cause them to become gay and also cause the SDNPOA to get smaller? And for the public, the idea that a nucleus might change its size in adulthood, maybe that seems kind of like, you know, unlikely. But as neuroscientists, we know, you know, that adult brains are changing all the time. In fact, even in animals, Brad Cook showed that, you know, there's a nucleus, the medial amygdala, there's a sex difference there, but if you take away the testosterone in

• 31:49Speaker 01

  males, sex difference goes away in just a matter of a few weeks. So Simon's work on the SDNPOA, also known as INA3, I won't bother with why.

• 32:00Andrew D. Huberman?

  Unfortunately, I remember the full name. Because my brain, it's the interstitial nucleus of the anterior hypothalamus, subregion 3. I'm not saying that to impress anyone. When you get to be 50, which I can now say that, you wonder why your hippocampus remembers certain things that are like basically totally useless to remember.

• 32:17Speaker 01

  I waste so many synapses on totally useless crap. But that's not, that's worth holding on to. You did well. So, but, so we don't know, it's a chicken and egg problem. We don't know if that happened, if they were gay because they had a small INA3, or do they have a small INA3 because they're gay? So what I liked about Dennis's autoacoustic emissions is pretty good evidence that that happened well before they had a sexual orientation. And the other thing I always liked about it is that, well... I mean, you can't imagine there's a social influence on, on digit and, and be, and

• 33:02Speaker 01

  nobody, nobody knew about this. So I wasn't worried that there were some little girls out there that looked at their hand and say, mm, gee, that looks kind of masculine, maybe I should be a lesbian, right? Because nobody knew this.

• 33:12Andrew D. Huberman?

  Until your paper was published.

• 33:14Speaker 01

  Yes, yeah.

• 33:15Andrew D. Huberman?

  I mean, as I recall, there, there was some like schoolyard stuff of kids looking at each other's hands and trying to decide who was gay and who was straight and.

• 33:22Speaker 01

  You know, every once in a while, to this day, on, on the internet, I'll look at them and there'll be a little ad over there other claiming to, to tell me something about my personality based on the, on, on, on digit racial link and it's just like, you know, please, uh, yeah, there's nothing to it. Don't waste your money, gang. And there's an aspect to this, this, this fact that, that the group differences were there, but you can't tell about differences between individuals, that, that I think is the hardest thing for scientists to communicate to the public at large.

• 33:52Andrew D. Huberman?

  Yeah, you, you have a really good way of explaining this to people because, and it's an important lesson just in reading statistics and, and making sense of data that, um, I'd love for you to give an example of how this plays out, perhaps in a separate example.

• 34:07Speaker 01

  Psychologists, they like to talk about a way of measuring how big a difference is between two groups. So this difference in digit ratios between men and women, it's, it's a relatively small difference. It's like, well, we measure it in terms of how many standard deviations apart are the two means of the populations.

• 34:25Andrew D. Huberman?

  The two averages.

• 34:26Speaker 01

  The two averages. And to give an example of that, everyone knows about the sex difference in human height, right? Among adults. So that's a huge sex difference. It's one where we're all aware of it and if, if nobody had told us it was such a thing, we'd notice it after a while, right? And that, that's because those two averages and those two populations are about two standard deviations apart. The standard deviation being a measure of how much variability there is in something. So that's a huge sex difference. And to give you an idea of what that means, if I had you grab a, a sample of a thousand people and I'm going to tell you one thing about each one of them, and that's their height, that's all. And now I give you the job, you've got to guess what sex they are.

• 35:12Speaker 01

  And I can tell you what you want to do to maximize your hit rate. Everyone who is five feet, five and a half, you're going to say those are men. And if they're less than that, you're going to say they're women. And you'll be right about 80% of the time. Which means you'll be wrong almost 20% of the time, right? And so everyone, you can, you can see that, that there's some predictive power there, but not, it's far from perfect. Well, this sex difference in digit ratios is half a standard deviation. So a quarter of that. And so that means there's much more overlap. And that, and, and we know that other things influence digit ratios too, not just prenatal testosterone.

• 35:56Speaker 01

  And so this is why there's no predictive value. I mean, so anyone who looked at their hand while we were talking about this and got worried, I don't know anything about your particular prenatal testosterone level, no matter what your digit ratio is.

• 36:12Andrew D. Huberman?

  What about bisexuality? People who identify as attracted to both men and women. And maybe we ask about first bisexual women, then bisexual men. Is there a pattern in digit ratios that leads anywhere?

• 36:24Speaker 01

  I mean, in those days, we didn't have enough people that identified as bisexual to have a reasonable sample. And it's interesting, and that's something that's changed, right? I mean, if you do surveys now, especially for among younger people, there are more people who report that they are bisexual than there were then. So, so I don't really have anything to say about them. The one thing I will say is I'm sure that even among lesbians, there's more than one pathway, more than one developmental pathway to, to, to become a lesbian or to become a gay man, right? I don't think there's just one thing. That's not how human behavior.

• 36:57Andrew D. Huberman?

  But you do think it's based on the data that it's biological?

• 37:00Speaker 01

  Based on that data, I think testosterone has a say, right? That it not as, doesn't mean it's the whole package.

• 37:06Andrew D. Huberman?

  Prenatal testosterone.

• 37:08Speaker 01

  Prenatal testosterone.

• 37:09Andrew D. Huberman?

  And the reason I ask that is, I mean, there are conditions that are not uncommon where someone has a particularly stressful, long phase of development where.

• 37:19Andrew D. Huberman?

  There's every reason to believe that their androgens are impacted negatively.

• 37:24Speaker 01

  Yes.

• 37:24Andrew D. Huberman?

  There's also every reason to believe that there are stretches of development where androgens are increased. Like, we know that people who do a sort of a contact sport.

• 37:36Speaker 01

  Right.

• 37:37Andrew D. Huberman?

  Or engage in anything that requires, like, deliberate aggression. I realize that real martial artists.

• 37:42Speaker 01

  Competitive.

• 37:43Andrew D. Huberman?

  No, competitive aggression, know how to, you know, sort of gate their levels of aggression so that they're not, they're not like in a fury, right? But we know that certain types of activities, competition, et cetera, I mean, there's no question that those can increase androgens. So you can imagine there's some plasticity postnatally. And that could be before puberty. It could be during puberty. And, and so that's testosterone, there, the body, as you said, you said something that, even as a developmental neurobiologist, I don't think I'd ever heard stated so clearly, and it's so important, that, that the rate of brain development from birth until age 12 is at least as fast as it was before we're born.

• 38:27Speaker 01

  Yeah, I mean, the, the way to really bring that home is to compare human brain growth and chimpanzee brain growth. So up until birth, the rate at which the brain size increases compared to body size is about the same in humans and chimps. And shortly after birth, the chimpanzee brain stops growing as fast and eventually asymptotes right away. The human brain continues that feverish fetal rate of growth until at least six years of age, maybe out there to 10 years of age. So people have pointed out that, in, in a real sense, human beings, children, are fetuses that are outside learning a whole bunch of stuff from other people.

• 39:11Speaker 01

  That's the real distinctiveness of our species, is, you know, we have this protracted childhood.

• 39:18Speaker 01

  And really intense social learning and as you say, a fetal rate of growth, even though we're not in the fetus anymore.

• 39:24Andrew D. Huberman?

  So I guess for me, the idea that behavior, exposure to things, you know, and I don't want to get into valence of negative, positive, but sure pesticides, but also, you know, schoolyard activities.

• 39:39Speaker 01

  Yep.

• 39:40Andrew D. Huberman?

  If you have, and we'll get to this, you know, five siblings and it's very competitive, who gets how much pizza, you know, I had one sibling, so it was a little bit, you know, there was competition, but it was different, right? You know, these things change hormones, hormones change the brain, the brain, as you're explaining, can impact sexual preference.

• 39:58Speaker 01

  What's great about studying hormones and behavior, right, is that sometimes you can control the hormone, in animals at least, but the hard thing about hormones and behavior that people don't understand is that behavior can affect hormones, as you say, in competitions, the winners afterwards are more likely to have higher testosterone and the losers will have lower. In elections, it's been shown that people whose candidate won the presidential election, their testosterone levels went up a little bit and the people whose candidate lost went down a little. And so you'll always have this cycle where the hormone alters the behavior and then the behavior alters the hormone and you always have to look for ways to try to pin down

• 40:41Speaker 01

  the order of effects and, you know, not always easy. The only thing I know for sure is that the brain remains plastic all of our lives.

• 40:52Andrew D. Huberman?

  Well, that statement is a significant one because I also believe that the brain remains plastic throughout our lives. It's always surprising to me that the hypothalamus remains plastic throughout our lives and I think that's worth perhaps double clicking on, so to speak.

• 41:07Speaker 01

  Yeah.

• 41:08Andrew D. Huberman?

  Because, you know, the idea that you can learn another language and your neocortex changes, or you can learn to juggle and your, you know, your motor cortex changes, your cerebellum changes, okay, like there's a lot of beautiful studies demonstrating that. But when I think about the hypothalamus, I think about it as something that's pretty hardwired.

• 41:28Andrew D. Huberman?

  By time puberty wraps up. But the more I learn and the more data that get published, the more surprised I am. I saw a paper just the other day that the neurons that control suppression of appetite, these POMC neurons in the arcuate nucleus, there's a population of them that are sort of undifferentiated that can become, let's just call it pro-hunger and by expressing some, a different peptide, neuropeptide Y. And that there's a lot of late-stage plasticity. And this may explain why people who reach a certain level of obesity may actually find that they're hungrier despite not eating food. So it's fascinating to me how these deeper brain structures may actually remain plastic.

• 42:06Speaker 01

  I think both your statements are true. I, I think it's probably true that the neocortex is more plastic than the hypothalamus, but it's a matter of relativity. And so as you say, the one thing we know is that there's plenty of plasticity there. The other thing I noticed, so I've, I've gone to society for neuroscience meetings pretty regularly every year since 1977. And after a while, I noticed something. Every year when I went to the neuroscience meeting, the brain was more plastic than it was the year before. Right? I mean, because there are more and more of these demonstrations and it's like, I, I, you know, I think synapses can come and go just about anywhere. And so hardwired, well, let's, let's, let's say there's, might be less plasticity in the hypothalamus, surely so. But that doesn't mean there's none.

• 42:53Andrew D. Huberman?

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• 43:38Andrew D. Huberman?

  What would that supplement be? And my answer is always AG1 because it has just been oh so critical to supporting all aspects of my physical health, mental health, and performance. I know this from my own experience with AG1, and I continually hear this from other people who use AG1 daily. If you would like to try AG1, you can go to drinkag1.com/huberman to get a special offer. For a limited time, AG1 is giving away six free travel packs of AG1 and a bottle of vitamin D3K2 with your subscription. Again, that's drinkag1 with the numeral one.com/huberman to get six free travel packs and a bottle of vitamin D3K2 with your subscription. What are some of the other effects in human studies of behavior impacting hormones

• 44:23Andrew D. Huberman?

  that come to mind for you? I mean, it's been a while since we've touched into this, and we haven't done it much on this podcast. I mean, obviously, competition, winners, losers, you explained the data there. What are some other scenarios? Just studies that have been striking to you or that have stood out over the years?

• 44:38Speaker 01

  I think for testosterone, I think the big ones have been have been competition, you know, between males. And, no, I don't, you know, I mean, there's a stress response, but that's a whole other thing.

• 44:52Andrew D. Huberman?

  What about sex behavior itself?

• 44:53Speaker 01

  In animals, at least, we know that that there's a relationship there, that that in in males, in males of most species, let's take rats, if you take away the testosterone, within a few weeks, they'll they'll stop mounting altogether. And if you give them testosterone, after a few weeks, they they start mounting again, right? So we know that that plasticity is there, and we know that it's driven by testosterone. But in in animals where they're in charge of their own testosterone, we've known for a long time that if a male is exposed to the odors of a receptive female, that causes a spike in their testosterone.

• 45:34Speaker 01

  And so that's kind of preparing them for maybe, maybe some, maybe I'll be lucky, maybe there's something coming down the pike. And so we know that that's a reciprocal relationship when the animal's in charge of the of the hormone.

• 45:50Andrew D. Huberman?

  For the longest time, thanks to your textbooks, and by the way, folks, Mark has authored some of the most important textbooks on hormones and behavior, developmental neurobiology. He's a true scholar of the whole field, and so immensely grateful to him that those textbooks have formed the backbone of a lot of solo episodes of the podcast. So, you know, the textbook version of male versus female sexual behavior has been a story about females having a circuit that goes from brain to body to control this thing they call lordosis, the arching of the lower back, the receptivity, the willingness to mate,

• 46:30Andrew D. Huberman?

  and the males having a circuit that goes from brain to spinal cord to body involving arousal, erection, mounting, insertion, ejaculation. I mean, your lab and others has really parsed this right down to the details. And yet, of course, people have sex that way, but also other ways. And so for a lot of people who aren't familiar with hormones and neural circuits and behavior, the sort of strict context kind of is, still forms the framework, you know? I mean, I've learned, and I'm now fortunate that this podcast has been around more than five years, so I no longer have to tap dance around things, right?

• 47:11Andrew D. Huberman?

  So people will say, oh, well, you know, there's this lordosis behavior in the female, she's receptive or not, he mounts, et cetera. And then there's gay men who have to have sex a certain way that mimics the female sex pattern of behavior. And so people do this one to one, right? Yeah. And I think that it's understandable why they do that if they're not educated. But how should we make sense of these biological circuits that are in the textbooks that define stereotyped, literally motor behavior? It's almost like saying like, like females have sex this way with males, males have sex this way with females, but then the caveat is always like, oh, but in humans, all that goes away. And there's these like bonobos that are a little bit more like humans. So did we waste all our time studying that stuff? I mean, really.

• 47:56Speaker 01

  And you're getting at exactly what every textbook author has to deal with, right? Which is, you know, as the old joke go, you, you, you, you look where the light is, right? So, we know so much more about the circuits that are involved in the motor behaviors, because they're relatively easy to trace, and relatively easy to manipulate, and relatively easy to, to study. We know lots about the motor patterns in animals. We know a lot less about the motivational patterns in animals, which in human sexual behavior is, I mean, in many ways, that's the whole show, you know? That's, that's really what's, and, and we don't really have good animal models of, of libido, right?

• 48:41Speaker 01

  And this was brought home to me many years ago now. I, I was on a session of 60 Minutes, the CBS News program. And Leslie Stahl was there in our lab. I mean, the producers had called me up and said, you know, can you show us a way that, that early testosterone exposure changes behavior permanently? And I said, sure, I can do that. Give me some time. So, I went to the lab and castrated a bunch of rats on the day of birth. I know how to do that. I'm not proud of it, but I, I know how to do that. And they came three months later. And, so, I, I showed them those motor patterns you talk about. So, here's a typical female.

• 49:23Speaker 01

  I've given her hormones, estrogen and progesterone, so I know she's gonna be receptive. And here's a male rat that I know has had lots of experience copulating. And Leslie immediately dubbed him Romeo. Okay, well, this is Romeo. And, it, it, she hates rats, by the way, so she, she was, she was very brave. And so, I, I drop a female on top of Romeo, and he starts mounting, and she shows the lourdesis posture, and it's all beautiful and easy. And we do that several, and I said, now, I'm, I'm gonna drop a male, a control male in. And Romeo, of course, you know... You don't know unless you try. He mounts several times and the male rat acts like nothing's going on. I mean, it's just a bored thing on earth and Romeo eventually

• 50:07Speaker 01

  gives up. Now I drop into the cage a male rat who I castrated on the day of birth, 90 days before, and I've given him the same hormones I gave the female to make her receptive. Romeo hops on and sure enough, a beautiful ordosis, right, of the sort that the control male never showed. So here, this neonatally castrated male is showing very female-like patterns. And Ms. Stahl kept asking me, would you say this is a gay rat? And it's, you know, I'm sitting there and I'm definitely in a tough spot because I don't think my rats have an orientation. I mean, we just saw Romeo happily mount any

• 50:52Speaker 01

  rat I threw in the cage because what do you know, you know, try your luck. And so, you know, she asked me, I knew she wanted me to say that, but I said, what I would say, I don't remember exactly what ended up in the final, what I would say is that this is a rat whose sexual behavior has been permanently changed because of something that happened to him a long time ago, at the very beginning of development. And really, that's the best I can do in terms of any rat model of sexual orientation. I don't think my rats have a sexual orientation. If I give the female those hormones, she's going to show ordosis to whoever mounts her. And my male rat, he will mount any rat he comes across, just in case he gets a ordosis out of them.

• 51:37Andrew D. Huberman?

  Well, good on you for not getting corralled into giving a particular answer. I've recently joined CBS as a correspondent. If we have this conversation on 60 Minutes, I promise to not try and enforce an answer. Romeo is an interesting case because I think for most people, including myself,

• 51:58Andrew D. Huberman?

  I thought that you were going to say that Romeo was willing to try to mount a female.

• 52:05Speaker 01

  Mm-hmm.

• 52:05Andrew D. Huberman?

  If she was receptive, he would mate. If not, he wouldn't. But I was surprised that he would try to mount a male as well. That doesn't align, at least with my experience of male human behavior.

• 52:17Speaker 01

  Certainly not. That's right. This is the thing that's distinctive about humans is we're not actually that particular about what particular behaviors we engage in, what motor behaviors. And we're overwhelmingly interested in who our partner is.

• 52:32Andrew D. Huberman?

  Mm-hmm.

• 52:33Speaker 01

  That is an overriding concern that I don't think my rats have. I think few animals do. Here's the, you're the anthropologist from Mars, and I tell you, here's a person that 50%, here's, whoever's the sexiest man alive this year, People Magazine, I don't know who that happens to be.

• 52:56Andrew D. Huberman?

  Well, this is an interesting discussion altogether because there's this, people have been lining up the images of these people and claiming that they're sort of like this effeminate drift.

• 53:04Speaker 01

  Ah.

• 53:05Andrew D. Huberman?

  That takes us back to a time in the early 90s when there was this sort of revision about male facial.

• 53:11Speaker 01

  Fascinating.

• 53:11Andrew D. Huberman?

  We can get back to that.

• 53:12Speaker 01

  Yeah, yeah.

• 53:13Andrew D. Huberman?

  But, yeah.

• 53:13Speaker 01

  Okay, okay.

• 53:14Andrew D. Huberman?

  It's not, the point being that it's not fixed.

• 53:16Speaker 01

  Who, yes.

• 53:16Andrew D. Huberman?

  Yeah.

• 53:17Speaker 01

  Well, whoever, let's say it's George Clooney. So here's someone that half the planet believes is an ideal sexual partner, right? But the other half of the planet finds him totally unacceptable, even if the behaviors they engaged in would be pretty much the same. And so, you know, in terms of positions and who's doing what to who's genitalia, et cetera, I mean, for most people, it isn't that there has to be one particular act. I suppose there's some, but for most people, there may be a variety of acts that they want to be engaged in with that other person.

• 53:57Speaker 01

  And their overwhelming concern is the gender of that other person, or the sex of that other person. You know, it's hard to have an animal model of that. I actually do know of one example in sheep.

• 54:11Speaker 01

  If you want to talk about this.

• 54:12Andrew D. Huberman?

  Of all things.

• 54:13Speaker 01

  Yes, oh, I, I, I noticed it. So, um, so Chuck Roselli out of Oregon, he's the one that's studying this very carefully. I guess shepherds have known for ages that in any herd, there are some rams who will not mount a female, ever, and keep mounting other males. And of course, to maintain a shepherd, uh, uh, to maintain a herd, you don't need every male to reproduce, so, but in the old days, they got, those males got sent off to slaughter, right? Well, um, hearing these rumors, Chuck did these tests where he would put a bunch of

• 54:55Speaker 01

  females that are in stocks, so they can't move, and they're all ready for mating, and he put a ram in with them, and most rams, of course, will mount the females. He, he puts in these rams that, that prefer males. If there's a variety of sheep's butts sticking at him, out at him, uh, he'll mount males, including sometimes, you know, having intermission through the anus and all the way to ejaculation, and, and he never mounts a female. In some cases, they'll have one of these, I'm gonna call them gay rams, I think, I think they have an orientation. He'll put this gay ram where there's a dozen females, and he might be in that paddock

• 55:39Speaker 01

  for 12 hours and never mount a single female.

• 55:42Andrew D. Huberman?

  Highly unusual for male rams.

• 55:44Speaker 01

  And these are not typical ram, it's like a small percentage of population, and, um, and I don't know how to explain that. I mean, you would think that, that these gay rams, that, well, you know, an ejaculation's an ejaculation, right? An orgasm's an orgasm, I presume they have orgasm. You, you would think that at some point, that, well, there's nothing else to do in here, I'll mount one of these ewes, and they never do. And I don't know how you can explain that, except that there's some aversive component that, that, that, that rams do care about the sex of their partner, and that, and that for these gay rams, um, there's some aversive component to that. By the way, Chuck told me, uh, not too long ago, there's a company.

• 56:28Speaker 01

  That has identified these gay rams and decided that instead of sending them off to slaughter, they're going to harvest their wool and sell them as and make them into clothing. So you can buy wool clothing that came from gay rams and know that you saved them from the slaughterhouse.

• 56:47Andrew D. Huberman?

  There's no response that's appropriate to that statement.

• 56:50Speaker 01

  And apparently, they're out of stock, so it's been a big success.

• 56:55Andrew D. Huberman?

  Actually, I can think of about 50 different responses to that, none of which are appropriate or have any real conceptual importance, so I won't say. Fascinating, because rams, while of course they have socio-dynamics, presumably there isn't a pressure, independent of reproductive pressure, to be a gay ram or a straight ram.

• 57:22Speaker 01

  And I guess I left off the kicker, which is Chuck eventually dissected the preoptic areas of these various rams, and he found a difference between the preoptic area of gay rams and straight rams, a difference in how they process testosterone. And exactly that part of the brain, the preoptic area, where Simon saw a difference between gay and straight men. So there may be something about the hypothalamus, the preoptic area, that has something to do with orientation, if we're talking about an organism as complicated enough to have an orientation, including sheep.

• 57:59Andrew D. Huberman?

  This is a particularly nice moment, not just for this episode, but for the entire podcast arc, because there are these moments that come up every once in a while where a larger principle shows up in a new way that I think is really important for people to understand. Across neuroscience, we see this push-pull, right? A flexor muscle, like the bicep, when it flexes, the tricep relaxes. When the tricep flexes, the bicep relaxes. These antagonistic relationships. You see this in the hunger circuit. I mentioned one earlier. Like hunger and feeling full are, they're like a push-pull. They're like a seesaw. And... And you see this over and over and over again.

• 58:43Andrew D. Huberman?

  It's a very consistent theme of brain function. And you said something that I was not aware of, but makes perfect sense. I just wasn't aware that there were, you know, data at the level you described, which is clearly there's an appetitive aspect to sex behavior. Heterosexual males wanting to have sex with females. Heterosexual females wanting to have sex with males and so on. Every derivation there. There's a desire. In species where there's strong pheromone and odor determination and receptivity stuff gets played out that way. It looks one way in humans. It may have some of that, but it plays out differently. Receptivity is communicated differently. Although odor may be very important in ways we don't quite fully understand.

• 59:27Andrew D. Huberman?

  But this idea that there's an aversive aspect to it. Right? I think this is important and it's something that I have not heard discussed before. And I think that sociologically it has relevance because I think that there are so many different aspects to the notion that our species, humans, come in gay and straight and perhaps bisexual varieties. We know that's true. Clearly. But there is this not uncommon theme whereby many people, I can only, you know, say many people, right? Not all, that the concept of mating with same sex is aversive to them. And that has shaped a lot of the landscape around this.

• 1:00:12Andrew D. Huberman?

  And I'm not trying to get political here. It's just, I think it's worth acknowledging that that may be a real phenomenon too. I'm not trying to justify mistreatment of anybody, but I think that we're never going to get where we want to go as a species societally until we really at least understand the biology and how to work with it. And so the idea that same sex

• 1:00:35Andrew D. Huberman?

  Sex, right, would be aversive as an idea to people. Some people are like, oh, well, they haven't been educated. Okay, perhaps, you know, but there may be a biological basis for that.

• 1:00:48Speaker 01

  I think the data is still out, but I think it's, to me at least, it's pretty clear that, for men at least, there's an asymmetry here. That experiment where I said, you know, who wants to have sex with George Clooney? Half the population says sure, the other half the population, never. If we reverse the experiment, what percentage want to have sex with Margot Robbie? And yeah, half the population, the men, would see her as a very desirable sexual partner. But, you know, the women too, would, many women would also, would at least consider the idea of having sex with her. And we know there are plenty of women who were straight in one part of their lives,

• 1:01:32Speaker 01

  and later, they fall in love with a woman, and now they feel like they're gay, right? So females, women, are more plastic in terms of their sexual longings and sexual orientation than men are. I'll be a little more specific. I think it's among males, where sometimes, for many males, not all, there's an aversive idea, that the idea of having sex with the same-sex partner is aversive. Now, of course, context matters, right? There's same-sex happening in prisons all the time, when, you know, if the conditions are enough. And I don't know where that aversive component came from.

• 1:02:17Speaker 01

  It could be that our society, maybe it's all socially inculcated, you know, again, before we're aware of it at all. But I think there's also at least the possibility that there's a biological component to it. And I think that's what Chuck was getting at, in that here's this difference in the brain. He doesn't know when the difference happened in the preoptic areas, but it seems to correlate with this idea that maybe these gay rams, no, they're not interested in having sex with her, they're, you know.

• 1:02:49Andrew D. Huberman?

  It's aversive to them.

• 1:02:50Speaker 01

  It's aversive, yeah. There's no other way to, I can't, I don't know any other way to explain how they choose never to, never once mount a female.

• 1:02:59Andrew D. Huberman?

  I feel like that the acknowledgement of a

• 1:03:03Andrew D. Huberman?

  The aversive pathway for sexual partner choice is as important as the acknowledgement of biological correlates of homosexuality.

• 1:03:15Speaker 01

  Yeah.

• 1:03:15Andrew D. Huberman?

  Because if this sort of conversation is ever to advance past the sort of like, okay, what's okay to say now that we're willing to say now, trust in science disappears. I really believe that. Now, of course, the problem is that people leverage fragments of what they hear in order to make arguments in favor of whatever stance they have. And that's the complication. That's why I like long form, because no matter what gets pulled out, we can go back to the full conversation.

• 1:03:41Speaker 01

  Right. And this makes you old fashioned, because that's not the world. I mean, our world seems to be hurtling towards this.

• 1:03:48Andrew D. Huberman?

  Yeah.

• 1:03:49Speaker 01

  Yeah, I mean.

• 1:03:50Andrew D. Huberman?

  World of snippets. People will notice that we have not used the word gender. We're talking about biological sex and sex, the act. And we're talking about male versus female partner choice. And we're talking about a desire for one or the other and an aversion to one or the other. And I think the aversion piece is an important theme. So here's a hypothesis, if I can come do a sabbatical. I'm due for a sabbatical at some point. It may be that in male humans, that there's a pathway or a molecule that serves as an aversive to sex with other men circuit, peptides, neurons, et cetera, that suppresses sexual desire and activates some level of disgust.

• 1:04:35Andrew D. Huberman?

  I'm gonna just say it bluntly. Might not be the same disgust that they would experience to something more aversive, but okay. And that in women, there is no such pathway. There's either desire for women or desire for men. But as you said, you know, statistically, women are more open, on average, to same-sex

• 1:04:58Andrew D. Huberman?

  Interactions and it may be because there's no aversive signal or the aversive signal has a less robust circuit.

• 1:05:06Speaker 01

  To me, that that would explain these differences, that these sex differences in who people are willing to have sex with. Your hypothesis fits the data.

• 1:05:15Andrew D. Huberman?

  I mean, it is true that in the like, the early 90s, for instance, when the first gay characters were on television, like the real first Real World, I'm really dating myself here, and subsequent characters started to dismantle some of the stereotypes that had been seen in like comedies in the 80s and things like that of the effeminate gay man.

• 1:05:34Speaker 01

  Yeah.

• 1:05:34Andrew D. Huberman?

  Right? What you saw was indeed that heterosexual women, as far as we know, seem to be more like generally accepting of gay men before heterosexual men embrace that as as typical.

• 1:05:51Speaker 01

  That's my impression, too. I think I think it's pretty clear.

• 1:05:53Andrew D. Huberman?

  Yeah. And then and then there's a societal shift and then it sort of becomes like, you know, like if you like, I spend some time on X, formerly known as Twitter, right? And there's some gay political accounts and and you just kind of notice like it's just people are like comfortable with it. Men and women seem to be comfortable with that, right? I mean, of course, you don't see a lot of attacks now. That's very different than what you would have observed, would have observed, for instance, in like the late 80s, early 90s.

• 1:06:22Speaker 01

  Oh, yes.

• 1:06:23Andrew D. Huberman?

  Right? Anyway, I think these are important biological phenomenon, this notion of an aversive pathway. You could imagine where societal standards or community standards or household standards might, you know, amplify or reduce like the the sort of expression of these things.

• 1:06:43Speaker 01

  I'm I'm sure they do.

• 1:06:44Andrew D. Huberman?

  Yeah.

• 1:06:44Speaker 01

  And and I'm sure, you know, cultures, you know, can amplify or reduce that component. The question is, you know, to what extent? I mean, and I don't, I don't think we know.

• 1:06:57Andrew D. Huberman?

  One thing that we haven't talked about, and it is a small percentage of people, but it's something that people think about, is this notion of sort of neither here nor there, kind of mixed sex, right? Is there a biological correlate of that? A graduate student my year, when you were my professor,

• 1:07:17Speaker 01

  Yes.

• 1:07:18Andrew D. Huberman?

  Nikki Osipka, Nicola Osipka, who was already famous for dog, training dogs for the Beastmaster Show. She's amazing. And had very well behaved dogs that she would bring everywhere with her. Studied a species of mole in Tilden Park that could transdifferentiate its testes into ovaries and back again. And I thought, well, that's like alien weird levels of stuff. But she would occasionally go over to UCSF when babies were born that were sort of, back then, they called them, no one uses this language now, pseudo hermaphrodite.

• 1:07:55Speaker 01

  Yes.

• 1:07:56Andrew D. Huberman?

  What is the deal with exposure to prenatal androgens and neither clearly here nor there genitalia?

• 1:08:04Speaker 01

  Yeah. So in most of those cases, we're talking about congenital adrenal hyperplasia, also known as CAH. And the congenital means it's present at birth. And the adrenal hyperplasia is referring to the fact that the adrenal glands are slightly larger. And the reason they're slightly larger in this case is because these are individuals where the fetus itself is not able to make some of the adrenal steroids that are important for staying healthy. And so the brain detecting, hey, where's the, where are the adrenal steroids that we need here, drives the pituitary to tell the adrenal gland, hey, we need more steroids. The adrenal

• 1:08:47Speaker 01

  gland gets the message, it hypertrophies, but the machinery isn't there to make those steroids. And so instead, the adrenal gland makes.

• 1:08:56Speaker 01

  Testosterone and other androgens. And actually, this can happen in either XX or XY individuals. And in XY individuals, people might not notice. But in XX individuals, what that means is that prenatally, her genitalia are being exposed to more testosterone than is typical. And so, under the influence of this extra testosterone, the clitoris may grow to be bigger than the typical clitoris. In some cases, in extreme cases, the phallus looks like a penis. And the skin around that area that would normally form the labia, again, there might be enough testosterone that it starts to look like a scrotum, except, of course, there

• 1:09:41Speaker 01

  are no testes inside there, because this is an XX individual. So, these individuals are identified at birth typically, especially in XX individuals. And there's an easy treatment, which is, oh, they can't make, you know, you do the tests, and you go, oh, they can't make adrenal steroids, so we'll give them some. And so, for the rest of their lives, they take adrenal steroids orally and get the benefits of that. And that shuts off the hyperactive adrenal gland, so that it shuts off the role of the output of testosterone. So, this is what's known as an intersex phenotype. And, yes, you're right, in the older literature, they were sometimes known as pseudohermaphrodite,

• 1:10:26Speaker 01

  huh? With the idea being whether a hermaphrodite is some, is an individual that can, that can function and reproduce, either as a male or female. And so, supposedly, they were pseudo, because they can't do that, because they have only ovaries. Well, you can imagine, first of all, being called hermaphrodite, nobody liked that. And if you ask them, well, is it better if I put this pseudo at the beginning? Does that, that make you feel like you're being less stigmatized? No. But a much more accurate description is to say that it's intersex. They have a phallus that's somewhere between a clitoris and a penis. And the skin around there is sort of like a scrotum and sort of like labia.

• 1:11:09Speaker 01

  So in the old days, once this got recognized, it was standard procedure to tell the parents, "Oh, this is an emergency. We need to do cosmetic surgery. We need to do surgery to make this little girl look like all the other little girls." You know, sometimes this surgery was, you know, there could sometimes be success for or not. Indeed, they knew how to make her look like other girls. But many of those intersex folks, when they grew up, were pretty angry that someone had done this surgery on them that wasn't needed medically, right? They were already taking care of the problem with the exogenous adrenal steroids.

• 1:11:54Speaker 01

  And so, "Who asked you to do surgery on my clitoris?" In some cases, the tip of the clitoris was missing. And so, these women grew up and were anorgasmic because they couldn't get the stimulation that they normally would have had. These days, there's much more, thanks to the activists like Cheryl Chase and others, who started getting the pediatrician's attention, "Hey, you need to think about that. You're doing elective surgery on an infant who cannot possibly have informed consent." And so, these days, it's more of a wait-and-see attitude, which I think is absolutely the... So, wait till they're grown up and ask them then if they want to have surgery.

• 1:12:36Speaker 01

  And my guess is, most will say no. I think that's been the pattern so far. So, these are females who were exposed to more testosterone than other females. So, does that mean that they're going to be attracted to women when they grow up? And the answer is, well, interestingly, if you look at groups of women with CAH, they are more likely to be same-sex attracted, to be lesbians, than the population at large. But most of them are straight. But what's interesting about that is, the older they get, as you keep surveying them, the higher the percentage of them that report having lesbian orientation.

• 1:13:18Speaker 01

  So it's possible, first of all, that indicates that, yeah, maybe prenatal testosterone increases the odds of them being lesbians when they grow up. And you also wonder, well, how many of them always had that same-sex attraction, but, you know, were following the pathway society laid out for them? And then, as they get older, they said, "Well, no, screw this. You know, I know who I'm attracted to. I don't have to fit the heterosexual mold." And so, it's, you know, that's entirely consistent with the idea that prenatal testosterone makes you more likely to be attracted to women when you grow up. There's another syndrome that I know you've talked about, which is androgen insensitivity

• 1:14:01Speaker 01

  syndrome, sometimes abbreviated, AIS. And it turns out, the gene for the androgen receptor that responds to testosterone and other androgens is on the X chromosome. And it may sometimes be that a woman will have an X chromosome that has a copy of the androgen receptor gene that doesn't work. And if she passes that X chromosome on to a daughter, then she's sort of duplicated herself. What's interesting is when that X chromosome is given to a son. In other words, that egg with an X chromosome that has a dysfunctional copy of the androgen receptor gene, if it gets fertilized by a Y-bearing sperm, now we have an XY individual.

• 1:14:41Speaker 01

  And as you've explained clearly in your Basics podcast, we know what'll happen in development. The Y chromosome will mean that the indifferent gonad will develop as testes. The testes will secrete two hormones that are going to guide sexual differentiation in the periphery, one of them being anti-malaria hormone, which is going to suppress the development of the malaria ducts, and therefore, no oviduct, no uterus will form.

• 1:15:10Speaker 01

  And the testes will also release testosterone, which normally would masculinize the body. But in this case, because there's no functional androceptor to respond to it, the testosterone goes round and round, but the body doesn't respond. And so the wolfian ducks don't develop. The periphery looks like a typical female. And these individuals, when they're born, often are not identified. Because the baby's born, the doctor does that very careful analysis by looking between the legs and says, "Congratulations, you have a girl." And they grow up to be girls, undetected. And they come to a doctor's attention when puberty happens.

• 1:15:52Speaker 01

  And all their classmates are having their period, but she's not. And so she'll eventually go to an OB-GYN, who will first do an exam, a vaginal exam. And he'll notice that the vagina is relatively short. Because the inner part of the vagina is normally derived from the malarian ducts. Well, in this woman, in this teenage girl, the malarian ducts never develop because of anti-malarian hormone. So there'll be no cervix that can be seen in the exam. And if he takes blood plasma levels, he'll see that this very feminine-looking girl, teenage girl, has very high levels of testosterone.

• 1:16:36Speaker 01

  And presumably testes. And if he does a karyotype, he'll see that she has an XY karyotype. And yes, there are testes in there, typically in the abdomen. And they're releasing lots of testosterone because there's no negative feedback to tell the brain, you know, "Hey, you can stop sending signals to the testes now." In these cases, you can ask, "Well, what's the sexual orientation of these women?" And the vast majority of them grow up to be straight. They are attracted to men. And they might be very, they're often very interested in having a family. And of course, they can't carry children themselves, but they can, you know, adopt and things like that. And so they're very much feminine, very straight women. But they're XY.

• 1:17:20Speaker 01

  But they're XYs. So the question is... Unfortunately, in terms of understanding whether prenatal testosterone alters our sexual orientation, these individuals aren't useful to us because we don't know if they're straight women because their brains could never respond to the prenatal testosterone, or are they straight women because they were raised as girls and socialized to be attracted to men. It's a fascinating syndrome, and there's at least one woman with AIS who's self-identified, who's a successful model, and there's another woman who wrote a memoir that's quite good.

• 1:18:00Speaker 01

  And what's interesting about it, when there's no testosterone response, they have very feminine faces, very feminine bodies, and so they're frankly quite attractive as women.

• 1:18:13Andrew D. Huberman?

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• 1:19:25Speaker 01

  I'm realizing, I'm drawing a model over here whereby we've got, again, accelerators and brakes, and I think we've got different axes. You know, I'm not trying to split hairs here, but I think for people who want to understand how hormones, sex, and behavior, sexual orientation fit together, it's very useful to think about, okay, you've got...

• 1:19:51Andrew D. Huberman?

  Chromosomes that drive, you know, our typical notions of male versus female. And you're providing some important caveats where the body appears one way, but it's an XY, you know, and there's almost every derivation of this has been Yes. observed, although not at a very high frequency. And then you've got choice of same versus other in terms of orientation, a key role of prenatal testosterone there. Maybe some cultural or other types of plasticity that might be biased more toward the female side. It seems that way, based on what you're saying. If I'm, you know, I'm willing to say it, if you're not, it does seem that way.

• 1:20:31Andrew D. Huberman?

  There's an aversive signal that kind of, that certainly in male sheep and other species and that, you know, matches my observations as a 50-year-old male who grew up in Northern California and, you know, I mean, again In this era. And the joke being that I'm, I can only speak from my own reference point on this. And then we have a bunch of different things about partner preference and, and that at some point, it almost seems like it departs from, well, it certainly departs from our sort of linear, like, okay, girls like boys, boys like girls, testosterone makes boys, estrogen makes, we're, we're, we're nowhere near there.

• 1:21:15Andrew D. Huberman?

  We're, we've left that station a long time ago. Exactly. And at the same time, we arrive at a place where I think we need better languaging to separate these axes because it is very confusing for people. And so that would be very useful if, if the fields of neuroscience and psychology would start to embrace the real world realities of, of, because I actually think the lack of specificity of talking about orientation versus biological sex and these, and these other aspects have, have led, I think that's the source of a lot of conflict, actually. Anyway, that's a, that's an editorial for another time.

• 1:21:57Andrew D. Huberman?

  In terms of biological impact on sexual orientation, one of the more striking findings that you've been talking about for a number of years that just kind of shocks at first, but then you get a lot of nods from people, is this idea that the larger the number of older brothers that a male has, the higher the probability that he is gay.

• 1:22:21Speaker 01

  It's been seen over and over. I mean, it's really one of the rock-solid findings in human sexuality that was first noticed by Ray Blanchard at Toronto and has been seen in many populations all over the world. So the way to emphasize the difference is if a baby boy is born today, if he has no older brothers, his odds of being gay when he grows up is about 2%, right? Pretty low. But if he had one older brother, his odds go up by a third. Okay, 2.6. And if he has two older brothers, they go up a third again, right? Now we're at 3.5. It turns out you've got to have like a dozen older brothers just to have a 50/50 chance

• 1:23:06Speaker 01

  from the same mother.

• 1:23:07Andrew D. Huberman?

  Right, so we know that it's not, you know, what they call now blended family or...

• 1:23:11Speaker 01

  We'll get to those in a moment. But this is what you see. So you get a big population of men. Here's a big population that have one older brother. How many are gay? And it's a small number. And the number that have two, still a small number, but more. And, you know, how do you explain that? We saw it when we did the surveys. I don't know if you remember, we also asked people how many older brothers and sisters they had and how many younger brothers and sisters they had. So it turns out in the general population, there are about 105 boys born for every 100 girls, right? That's also very consistent.

• 1:23:51Andrew D. Huberman?

  105 boys born for every 100 girls.

• 1:23:53Speaker 01

  That's right. So there's... Or put it another way, if you want, I can guess the sex of any baby that's going to be born, and I can be right more than 50% of the time, because I'm always going to guess boy, right? Because 51% of the time, it'll be a boy. For straight men, you total up all the older brothers they have and all the older sisters, and there's a ratio of about 105 older brothers to 100 older sisters. For the gay men... It turned out there were 140 older brothers for every 100 sisters.

• 1:24:28Andrew D. Huberman?

  Help frame that statistic for people. So you gave us the one older brother, what the probability was.

• 1:24:34Speaker 01

  Right.

• 1:24:34Andrew D. Huberman?

  It's a third increase. You go from 2% to 2.6. Is it a linear increase as you increase the number of older brothers? Do you just start increasing the probability at every, with every older brother? Or are there, is it sort of a step function?

• 1:24:47Speaker 01

  It is, in fact, a linear progression. So at that rate. So Ray's worked that out. Of course, it's hard to find men that have had more than four or five older brothers, especially these days. But it turns out in the Kinsey surveys, Ray went to the Kinsey surveys way back then. You know, those interviews were incredibly thorough. And so they have a record of how many siblings of each sex every one of those men had. And you can see it there, too. And it's another one of these cases where I tell you this and you tell me, well, I know somebody who has two older brothers and they're gay. Is that why?

• 1:25:21Andrew D. Huberman?

  Or I know somebody with three older brothers and they're not gay.

• 1:25:24Speaker 01

  Absolutely. So you tell me, oh, I know somebody who has two older brothers and he's gay. Is that why he's gay? And I really can't tell you. There's no way to know because, in fact, most men with two older brothers are straight. Right? Again, it's one of these instances where it gives you no predictive power about one individual, why they are gay. Ray Blanchard has done the statistics and their estimate is of all the population of gay men, about 1 in 7 are gay because their mother carried brothers before them. And what I mean is those same men with the same genotype, same genes, if their mom hadn't had older brothers before them, they'd be straight today.

• 1:26:07Andrew D. Huberman?

  Statistically speaking.

• 1:26:08Speaker 01

  Statistically. But you know, you show me a picture of the gay men's chorus and I can't point out which man is gay because of that because there are other factors that can influence whether someone grows up to be gay. So again, it's one of these things where the statistical comparison is of great theoretical importance, even though it offers no predictive value for a given individual.

• 1:26:34Andrew D. Huberman?

  So we know that males engage in much more rough and tumble play when they're younger, just like rats, just like monkeys. This is a fact. It's related to testosterone exposure.

• 1:26:46Andrew D. Huberman?

  If a boy has older brothers, there's a decent chance he's engaging in more of that than if he has a sister. And given what you said earlier, that in humans, the brain continues to develop at a massively accelerated rate even after birth, up to age six. Testosterone has an influence, behavior impacts testosterone. Okay, they're not in puberty yet, but you could imagine this has an impact. So the experiment becomes for boys that had two or more older brothers, but were not raised with those older brothers. Does the effect hold of them having a statistically greater probability of being gay?

• 1:27:26Speaker 01

  It's a beautiful hypothesis. And you first hear about this, and that's the first thing you think, well, maybe the younger brother got bullied, or...

• 1:27:34Andrew D. Huberman?

  Or beat up his older brothers.

• 1:27:36Speaker 01

  Maybe the older brother somehow inhibited the younger brother from developing in a full masculine fashion. But it turns out Tony Bogart started looking at these data, and he started asking, well, what about stepbrothers? Do older stepbrothers make any difference in the odds of sexual orientation? And the answer was a clear no. On the other hand, older brothers who came from the same mother, but were raised apart, had just as much of an effect as those that were raised with. So it does not seem to be socially mediated. In fact, Ray Blanchard and Tony Bogart have come up with a very plausible hypothesis called the maternal immunization hypothesis.

• 1:28:18Speaker 01

  And it runs something like this, that, you know, the first time a mother carries a son, that son is carrying some genes that her immune system has never seen before. All the genes on the Y chromosome, there's no way her immune system could have seen it. And as long as that first son is in utero, her immune system never sees it. But inevitably, at birth, whether it's cesarean section or vaginal delivery, there's always blood and there's always mixing of blood. And so at that point, the mother's immune system is going to see these male-specific antigens that it's never seen before. Of course, it's going to regard it as an invader and it's going to start making antibodies to it.

• 1:29:02Speaker 01

  So their hypothesis is that each time a woman delivers another son, her immune system is going to generate more of these antibodies. And if she has a subsequent son, antibodies cross the placenta just fine. And so, in fact, the placenta very actively sends antibodies across to protect the young. And so that would mean that her antibodies are going into this third son and somehow altering the development of their brain. And the strong evidence they found in favor of this is that in women who have sons where there's this pattern that looks like that might have happened, it turns out they have

• 1:29:43Speaker 01

  higher levels than control mothers of antibodies to a male-specific antigen, quite specifically, an antigen to a protein called neuraligand4Y. So adhesion molecule. Exactly. You know that neuraligands are important for synapse formation. And it turns out there are several copies, not unusual in humans. And this one, neuraligand4, there's one on the X chromosome and one on the Y chromosome, and they're slightly different. And so the fact that these mothers are making antibodies to this male-specific antigen and that in their particular family, it looks like subsequent sons were more likely to

• 1:30:26Speaker 01

  be gay, you can imagine that's what's going on, that her immune system has perturbed the development of that subsequent son enough that when they grow up, they're more likely to be gay. Whatever the mechanism is, it has to be that it's the mother's body that is remembering how many sons she's carried before them. Right? And it's got to be the mother's body that somehow is doing something to perturb the development of her subsequent sons to make them more likely to be gay. It's a fascinating idea, and it also gets at that same theme that I mentioned before. There are lots of different developmental pathways to end up being gay or to end up being straight. And there isn't going to be one cause of anything in human behavior, and certainly not of sexual

• 1:31:11Speaker 01

  orientation. But I think the evidence is looking pretty strong that for women at least, prenatal testosterone does have a say. And we know that in men, the mother's body has a say in whether they're going to be gay or straight when they grow up.

• 1:31:28Andrew D. Huberman?

  The result is so cool because, once again, it spits in the face of these, like, kind of reflexive assumptions. For instance, you could imagine, and I probably grew up hearing like, oh, you know, he was raised around a lot of girls or something, you know, had a lot of sisters, or he had an older sister, or three, right? Or dad left the house, you know, I mean, this didn't happen so much in the 70s and 80s, but it was more frequent in the 90s, you know, back then it was called broken homes. Now people will be like, what are you talking about? Like, everyone knows somebody divorced, right? So, but back then it was more rare, and there was this idea, like, lack of male influence.

• 1:32:06Andrew D. Huberman?

  And of course, there are important, I believe, gender-specific influences on kids in terms of upbringing, but in terms of the stereotype that seems to have largely dissipated, but that, you know, like, having an older sister or three would make a son more likely be gay. It's exactly the opposite when you look at the biology.

• 1:32:26Speaker 01

  Yeah, I mean, Ray's looked at that very carefully. And so, older sisters don't matter, and neither do younger sisters. And here's the other thing, that younger brothers don't matter, right? So, no matter how many younger brothers you have, that doesn't change your odds of being gay when you grow up. So, it's, that's why I say, it's got to be the mother's body that is remembering, and it doesn't seem to be socially mediated. It is, you know, independent of that. It is nature having its say.

• 1:32:55Andrew D. Huberman?

  Males with congenital adrenal hyperplasia, we didn't talk about that. And perhaps more important is to talk about males and females with congenital adrenal hyperplasia but are heterozygotes. So they have one functional copy, one non-functional copy. And the reason I raise this is that it's very common. It's one in 12.

• 1:33:14Speaker 01

  Huh.

• 1:33:15Andrew D. Huberman?

  One in 12, which is, it seems like an outrageously high number, but it's one of the things that is immediately screened for, maybe not as much as some other, you know, blood-related diseases and things like that.

• 1:33:28Speaker 01

  No, I didn't know that, but, but, but, but I can say, I mean, you have to remember, actually, there are several different genetic mutations along the pathway of making adrenal steroids that can go wrong. And so there are several steps that have to be there for them to make adrenal steroids. So, so number one, there's more than one site where the mutation would be carried. And of course, the heterozygotes are, you know, may have no symptoms whatsoever, and so they, they may reproduce just fine.

• 1:33:56Andrew D. Huberman?

  We know this, that, that, sorry, I should be clear, because people are probably thinking, wow, one in 12. Both males and females that carry one mutant copy of CAH are capable of healthy reproduction. There are some hypomorphic phenotypes, some people make more androgens, some people have a sustained stress response. It's not very well studied, but it is very common, which I found interesting.

• 1:34:21Speaker 01

  Another reason why the carriers are so common is because typically there's no, no phenotype, or if there is, it's subtle, and so it doesn't come to the attention of any, any physicians. It's only when two defective copies of the gene come together in one offspring that there's no adrenal steroid production at all, and then things happen enough to get the attention of the doctors.

• 1:34:42Andrew D. Huberman?

  Yeah, I've looked into this, and it does seem like one mutant copy of CAH is, is you find it just statistically more frequent in professions or sports where there's a requirement for.

• 1:34:57Andrew D. Huberman?

  Long-duration stress tolerance, which makes sense.

• 1:35:00Speaker 01

  Yeah.

• 1:35:01Andrew D. Huberman?

  Right? I mean, so some of these genes could confer an advantage.

• 1:35:03Speaker 01

  Yes.

• 1:35:04Andrew D. Huberman?

  Some could confer a disadvantage.

• 1:35:05Speaker 01

  Right.

• 1:35:06Andrew D. Huberman?

  In different settings.

• 1:35:07Speaker 01

  And that there might be a heterozygote advantage. I mean, you know, the classic example of sickle cell anemia, right? Where being a heterozygote for that gene confers an advantage. If there's malaria in the area, you'll be less likely to succumb. Things go wrong when two copies come together in one individual and that's when the the blood cells are especially affected. And things go wrong when an offspring gets two such copies. And which is relatively rare, but it does happen. And in that case, then the offspring is very sick.

• 1:35:40Andrew D. Huberman?

  Did you ever do the head transplantation experiment on the finches?

• 1:35:44Speaker 01

  That's amazing what sort of a memory you have. No, no, I never did.

• 1:35:48Andrew D. Huberman?

  You want to explain what this was? Because I'm not going to do it correctly, but I remember you wanted to do an experiment where you were going to transplant finch heads.

• 1:35:56Speaker 01

  Well, people.

• 1:35:57Andrew D. Huberman?

  And I thought it was the coolest experiment ever because it was going to be done as embryos. So, no, it was not taking heads off of birds.

• 1:36:05Speaker 01

  Yeah.

• 1:36:05Andrew D. Huberman?

  It was an embryo experiment. But I think we should talk about the backdrop of this. Male birds of a certain species sing. Female birds don't.

• 1:36:15Speaker 01

  Right.

• 1:36:16Andrew D. Huberman?

  So, you wanted to embryonically put a female head on a male body, a male finch head on a female body, and you wanted to swap head bodies of these embryos. Tell us the experiment, Mark.

• 1:36:31Speaker 01

  I'm certainly looking like the mad scientist.

• 1:36:33Andrew D. Huberman?

  Well, let me tell you. Wait, wait, hold on. Crazier things have been done with US tax dollars, like rainbow mice, mice that glow, you know, 215 different fluorescent colors to identify different cell types. I mean, I could go on and on and on. I think this experiment has a purpose to get at a principle that can't be understood any other way. So, it's not just tinkering for the sake of tinkering.

• 1:36:59Speaker 01

  In fact, people do those sorts of transplants in birds. So, a very famous neuroscientist from France, Nicole Durand, did these experiments where she would open up. Chick embryos and quail embryos. And she could scoop out part of the nervous system from one and implant it in the other. And she'd know when she had done it right. She had a way of telling the cells apart under a microscope. Plus, when they grew up, here you'd have this white Leghorn chicken with a streak of brown feathers. Right where she- Was it called a quicken? B- sorry. Couldn't help myself. Here you'd have this white Leghorn chicken with a streak of brown feathers in the middle that were derived from the quail.

• 1:37:41Speaker 01

  And so it is possible to do those sorts of swaps. And of course, this is what's so great about working with birds is their embryos are, you know, easy to get to for the first 21 days or so. So people had done those sorts of experiments. There was a question about sexual differentiation of the brain in birds. Because the, and I'll tell you why it turned out I didn't need to do that experiment. And it wouldn't have shown what we wanted. That is, so there are, sometimes you'll see in the news, someone will find a genandromorph in birds, yep. Genandromorph. So half female, gen, and half male, andro.

• 1:38:24Speaker 01

  And when it happens in cardinals, for example, it's like the animal's been split down the middle. No. Yes. Where the one side is the bright red of a male with the crest, et cetera, and the other side isn't, right? So these occur occasionally. And our best understanding of what happened there, first of all, the sex chromosome is a little different in birds than mammals, I'm gonna gloss over that. But our best understanding of what happened there is this is a case where two embryos, one that was carrying male sex chromosomes and the other female sex chromosomes, came together at an early stage. And so what we have is a mosaic animal. Where one side is genetically male and the other side is genetically female.

• 1:39:09Speaker 01

  Now, in a mammal, if that happened-

• 1:39:13Speaker 01

  The testis on the male side would masculinize everything by using hormones. The clue that something else is going on in birds is that, in this case, you know, there's not been this blending. And when Art Arnold and others looked at the brains of Janand remorphs, sure enough, the sex differences where this region, HVC, for example, is, tends to be larger in males and females. In these animals, it was larger on one side of the body than on the other. So they were indeed, you know, split. Well, this, this suggested that gonadal hormones were not in charge of sexual differentiation.

• 1:39:58Speaker 01

  And so what I wanted to do, and never figured out quite how to do, was to take a male brain and put it on a female body and vice versa, to ask what sexual differentiation will be like. Will the whole body listen to the brain and become male? Or will the gonads? It was a crazy experiment where if I could dissociate what the sex of the gonad was from what the sex of the brain was and what would happen. But it turned out, you know, I, I didn't have the good hands that you would do, for example. I never learned how to do that experiment. But one resolution of it is, one of the things we now know is going on in birds, is that

• 1:40:42Speaker 01

  in some cases, it's the brain itself that's making the hormone and is masculinizing itself. So in birds, there's pretty good evidence that brain sexual differentiation happens because the genetic sex of the brain determines how much hormone, including testosterone and estrogen, is getting made locally, and that that then is driving sexual differentiation. And that's why you can have, you know, one side of the brain is male and the other side is females. And that just doesn't happen in mammals. That's the mechanism, once you start using gonadal hormones to direct sexual differentiation, you can end up with that sort of mosaicism, which is maybe too bad. I mean, there are carnival acts where supposedly one side of the body is male and the other

• 1:41:27Speaker 01

  side is female, and those have been around for quite a while, but that's a different thing.

• 1:41:32Andrew D. Huberman?

  I'm gonna give you two real world examples. Real because... I was told them and I believe them. In anticipation of our conversation today, I ventured into some corners of the internet. I kind of wish I hadn't. But, you know, in gym culture, bodybuilding culture, there is a subset of people, I don't recommend it, that take synthetic androgens, anabolic steroids of different kinds and in different combinations. And again, I don't recommend people do this, but it's entirely different than hormone replacement therapy or something like that. Like experimentation with high dosages of different types of testosterone derivatives.

• 1:42:17Andrew D. Huberman?

  And my interest in understanding a little bit of what some of the general observations are there is a naturally occurring experiment with some thematic averages, which is geek speak for like, if one person reports something, it means nothing, but if hundreds of people or thousands of people validate that experience, you think, well, this kind of, you know, these aren't controlled studies, but nonetheless, might be interesting. And those communities have long talked about how different forms of androgens have different effects on psychology. And in particular, these days, you can find a lot of discussion in those communities of certain anabolic steroids, trenbolone in particular, that causes aggression, but

• 1:43:00Andrew D. Huberman?

  that is well-known for causing otherwise self-reporting as heterosexual males to start wanting to have sex essentially with males or females. There's an effect that seems reversible when they stop. I mean, it seems generally associated with a kind of a hypersexuality. Yeah. So that's an important variable, right? So there's all sorts of variables there. So that's one observation that that makes me wonder if the adult brain is still plastic at the level of the hypothalamus to androgens later in life. Now, this is not to say that the many now millions of men who are taking testosterone

• 1:43:42Andrew D. Huberman?

  replacement, which is very, very common, doing that safely with doctors' support, et cetera, they're not trying to boost things into superphysiological range, but it's a naturally occurring experiment with very few controls and only anecdotal reports, but it suggests that the adult hypothalamus

• 1:44:02Andrew D. Huberman?

  Is still androgen sensitive in ways that could drive pretty powerful changes in behavior and perception.

• 1:44:10Speaker 01

  And we know that is true because back in the previous century, Julian Davidson at Stanford, actually, in the physiology department there, was among the first to do these double-blind placebo-controlled studies in men who had lost their testes for one reason or another, accident or cancer, things like that. And so, double-blind means neither the man nor the physician who was interacting with him had any idea whether he was getting the placebo or the testosterone. And that's, of course, really important for coming up with conclusions. And they concluded that, in fact, the men who were getting testosterone definitely

• 1:44:53Speaker 01

  reported feeling better, feeling more energetic, having a higher libido, and they definitely felt better overall. And Julian said, sort of the joke is, that even though it was, men were supposed to be blind to which treatment they were getting, they always knew. They always knew when they were getting the testosterone because they felt so much better. So, we know for certain that testosterone does have effects on the adult brain in many of these cases, right? These were men, prostate cancer cases, who were elderly yet and still, they still responded to that.

• 1:45:30Andrew D. Huberman?

  Yeah, one thing I learned from your textbook was that, you know, this idea that testosterone diminishes with age is largely true, but the rates are highly variable and that, you know, there are some individual points on the scatter plot whereby you'll see somebody in their 70s or 80s whose testosterone is very similar to someone in their 20s or 30s. Now, everyone nowadays talks about how testosterone rates are dropping, so it's a, you know, it's, these are older studies, but.

• 1:46:00Andrew D. Huberman?

  It suggests that there's a tremendous amount of variation. We also know that absolute numbers don't necessarily dictate how people feel. In fact, the CEO of a very, very, very successful company, not a tech company, an entertainment company, came up to me once at a private party and said that his testosterone was down in the low 300. So this is approaching the lower end of the reference range, but he feels great. And I said, if you're willing, like, what variables are we talking about here? And he explained, you know, vigor, and he explained, you know, libido, and he explained, you know, general enthusiasm for life. And I said, well, I wouldn't change a thing in that case, right? I mean, he's a perfect case whereby low end of normal is not a problem.

• 1:46:43Andrew D. Huberman?

  And who knows, maybe had he taken more, he would have aromatized more to estrogen and he wouldn't have felt as good, for instance.

• 1:46:49Speaker 01

  No, I agree. I mean, if it ain't broke, you know, leave it alone.

• 1:46:52Andrew D. Huberman?

  Yeah, I think it's something that doesn't get mentioned enough.

• 1:46:54Speaker 01

  But you also point out why humans are such lousy research subjects, because there's so much variability going on. So what I can say is that for the decline in testosterone levels in men, first of all, it's so much more gradual compared to what happens to women at menopause, right? There's no comparison whatsoever. And there is incredible amount of variation across subjects. And so, once again, even though you can say statistically, we know this is a trend, I can't make, you tell me someone 71 years old just to pick on me, I can't predict what their testosterone levels are going to be like, or not very well.

• 1:47:34Andrew D. Huberman?

  Another sociological observation from the internet.

• 1:47:38Speaker 01

  Everything on the internet is true.

• 1:47:40Andrew D. Huberman?

  Certainly not everything on the internet is true. I know you were being sarcastic, and certainly not everything on the internet is informative. But clusters and averages are interesting to me. There's a meme, which I find interesting, vis a vis this type of conversation, whereby, I think it was a A martial artist, a MMA guy from either Russia or some eastern country, excuse me. The meme is, it goes something like, "Send two, three years to Dagestan and forget." A guy is talking about how he wants his kid to be good at wrestling, and so he's gonna send him to Dagestan where apparently the training is very intense. And the meme goes, "Send two, three years to Dagestan and forget." And he said, "I'm gonna send him there for a few weeks."

• 1:48:24Andrew D. Huberman?

  And then, and the guy goes, "No, no, no, send two, three years to Dagestan and forget." And that meme, which is, it's not a cartoon, it's a guy actually speaking in that context, has been, you can find extensive compilations of people showing kind of effeminate boys, dancing, doing kind of theater-type activities, and then it transitions to, "Send two, three years to Dagestan and forget." The idea being, returning to the beginning of our conversation, that there may be more plasticity early in life, and that masculinization of behaviors, stereotypically defined, okay? I want to be very clear. The idea being that that's very plastic early in life. Okay.

• 1:49:08Andrew D. Huberman?

  I think this is interesting and important to observe, because when I was a kid, my mom, she still tells me this story, but she's told me this, verified this for many years. We had a pediatrician, this was in Northern California, this is just a mile or two away from Stanford School of Medicine, and my pediatrician said to her, "You have a boy, Andrew, and there are three very important things in raising him." And these were his words. "One, don't let him ride motorcycles."

• 1:49:45Speaker 01

  I agree.

• 1:49:47Andrew D. Huberman?

  "Two, don't let him drink soda, too much sugar." "Okay, fair." And he said, "Three, don't let him do theater." The implication being that boys who do theater have a higher probability of becoming gay.

• 1:50:03Speaker 01

  Yeah.

• 1:50:03Andrew D. Huberman?

  Now, that was, I was born in 1975, okay?

• 1:50:08Andrew D. Huberman?

  He gave this advice to every parent of a male. And I say that to kind of frame people's understanding of where we were versus where we are. And yet, this meme is, I wouldn't say rampant on the internet, but has a fair amount of support for it in the sense that I think there's still the general belief that certain activities can bias sexual orientation. And I just want to zoom out and

• 1:50:37Andrew D. Huberman?

  ask, acknowledge the idea that the brain is plastic to androgens, behaviors impact androgens. So, not trying to corral you into a given answer, but I think we've come a certain distance in this, but we haven't really come that far.

• 1:50:53Speaker 01

  Well, and of course, there's no doubt that the younger brain is more plastic. I mean, there's, there's no way around that. But, but, you know, in terms of what one can do, there are limits. And, and in terms of sexual orientation, I, I can tell you, people look really hard for any social correlates. You know, you, you talked earlier about the, the dad that's missing, or, or even Freud talked about the overly coddling mother and, and the dismissive father. That might make a boy more likely to be gay. And so, people have looked for those sorts of correlates. The data just aren't there. I mean, it's really, which, which I think is interesting and kind of strange,

• 1:51:34Speaker 01

  because you'd think that if, if the social influence was that good, that, that, that you'd find something. And so, in terms of sexual orientation, I, I think the data are pretty weak. However... In terms of other expressions of male-like behavior, clearly, culture and family has a say, right? I mean, they clearly make an influence, I mean, in terms of what boys are supposed to do. I would say probably the only sex difference that will persist and that almost certainly is due to biological factors like testosterone is, you mentioned already, rough-and-tumble play. Across so many species, you know, you put a bunch of males together and there'll be

• 1:52:16Speaker 01

  a lot more physical activity than if you put a bunch of females together. And an interesting thing happens if you put it in a mixed group, and it doesn't matter whether it's monkeys or rats, the overall play will be intermediate. It's like the girls calm the boys down and the boys ramp the girls up a little bit. And so, that might be, you know, one that's going to be pretty hard to corral with social influences, but virtually every other expression of masculine behavior, of course, you know, culture and family make a difference. I don't know, you know, I'm gonna suggest anyone send their child to...

• 1:52:55Andrew D. Huberman?

  August 10th, 2, 3 years, I forget.

• 1:52:57Speaker 01

  Yes, thank you. Thank you for saying it.

• 1:52:59Andrew D. Huberman?

  The original statement, it was a real statement in a discussion, was aimed at something else. It's been co-opted for this.

• 1:53:05Speaker 01

  Of course it was.

• 1:53:06Andrew D. Huberman?

  Like, this is the form of, you know, intervention, or whatever you want to call it. Okay, let's set the internet aside and let's talk about a different upbringing for a moment, which is yours.

• 1:53:19Speaker 01

  Oh.

• 1:53:20Andrew D. Huberman?

  As a scientist, you have a somewhat unusual trajectory in the science. So, where were you born?

• 1:53:28Speaker 01

  In the Ozarks, in Springfield, Missouri.

• 1:53:31Andrew D. Huberman?

  Oh, I was about to say, where are the Ozarks? I know where they are, but to orient our international audience...

• 1:53:36Speaker 01

  Southern Missouri and northern Arkansas. So, it's famous because it's hill country and so, very hilly...

• 1:53:44Speaker 01

  Very much like the Appalachians, both in terrain and in culture, actually. So, no, I was born in the Old South, in a working-class family. No one in my family had ever, well, no one in my mother's generation had finished high school, much less college. And, you know, I was always a little bit different because I was so much more interested in reading than, all my cousins say, all they remember about me when we were growing up is I always had my nose in a book, right? That phrase. So, and I, as I get, and I didn't choose that. I didn't choose to like reading, but I always did. And I always loved school.

• 1:54:28Speaker 01

  And so, and I will say, I had a great family that was incredibly supportive of me doing whatever I wanted to, right? That that would, that would be fine. And as I look back, I realize, and I predict you'll find this too, the older I get, the more I realize how much luck matters and how many very fortunate things happened to me, right? So, the first question is, I end up going to Yale College. What? A working-class fam, working class. So, my folks were blue-collar workers. I mean, for complicated reasons, I was raised by my grandparents.

• 1:55:10Speaker 01

  He was a construction worker and she worked in a food processing plant. And so, they once told me that maybe altogether, they went to third grade, right? They got that far. But they were clearly smart and great people, and they were very supportive. And, and so, here's where, here's an incredibly lucky episode that happened to me. So, when I was a junior in high school, I go to the Central High School Library, and I volunteered there after work to put away books. And the librarian tells me, oh, there's this book you might be interested in. And she shows me this really thick paperback made up by the College Board. So, this was the first year that the College Board had put together this book showing

• 1:55:55Speaker 01

  all the colleges in the United States with little burbs about them. And she said, you might want to look at that. And I opened it up, and I see that for all the colleges, there's a paragraph about financial aid. So, I read that entire book.

• 1:56:12Speaker 01

  From front to back, except I only read the financial aid part. Because at the time, my grandfather passed away. And so my grandmother and I, our only income was social security. Right? That was, that was, that was our livelihood. And, um, and so I read financial aid, every one. And I get to the end. They're, in this first edition, they were in alphabetical order, which makes no sense. But that's how it was. I get to the end, and the one for Yale College, it's like one of the shortest listings there. And it says, basically, we're committed to making sure everyone admitted will get the financial aid they need. This is me. This is what, this is where I need.

• 1:56:49Andrew D. Huberman?

  You had to read the whole book just to get there?

• 1:56:50Speaker 01

  Well, I, the, the next entry was Yeshiva, which I thought, well, that's a strange name. But if, if they'd had that paragraph, I, believe me, I would have been applying there, uh, which would have been fun, too. And so, I, so I go to my counselor and I say, well, and I'd never heard of Yale. I mean, I associated it with locks. Right? I'd heard of Harvard because of Kennedy, but, you know, nobody in my family talked. I go to my counselor, her name was Jean Walker, and, and, and she says, that's an Ivy League school. Huh? What does that mean? And she, she, she tells me. And to her credit, she doesn't say, that's stupid. You're never, you know, why, why, why would you be doing that? She says, you know what? You should apply for early admissions this year. Early admission? I know. Okay. So I apply for early admission. I don't get it. So, okay.

• 1:57:35Speaker 01

  But I'll try again next year because that paragraph, it's, it's really got it under my skin, and this is what I need. So, apply the next year. And this time, they ask me for an interview. And I'm, I'm, I'm to have an interview with Dr. John Ferguson. I'm to call up his office and arrange for an interview. And I'm sitting in French class with my friend Dale, and I'm telling him, I'm supposed to make an appointment with Dr. John Ferguson. And the French teacher, who was one of my letter writers, Mrs. Fisher, she overhears this, and she says, what on earth? Why would you go see John, Dr. John Ferguson? Because she knew, but I didn't, he was an OBGYN.

• 1:58:14Speaker 01

  And I, you know, sort of sotavochae, well, you know, oh, well, I know John. He's an old family friend. I used to babysit him. And, you know, well, I'll be calling him. So I'm sure, I don't remember the interview with the man, right? I mean, I don't remember a thing about, but I'm sure he told him I was, you know, the greatest thing on earth because I'm sure he gave me as strong a recommendation as he possibly could. And, and so I got in and they, and they were true to the word. They sent me, you know, this, send me this thick letter with all these, all this financial aid. And so, and they didn't expect my family to contribute anything, right?

• 1:58:56Speaker 01

  So it was, it worked out and, and, you know, and what happened? I have mixed feelings about Yale because I benefited so much. I mean, and I'll, I'll credit myself with this. I went with the right attitude, right? Which is they've made a mistake. Mrs. Fisher got me in and I'm, I'm not going to screw this up. And, and indeed, you know, I, I, you know, Andy, I want to know everything. I, I want to know about art and literature and all the sciences. It was, I mean, I, I was hungry and I, so, and I went with the attitude is, man, all of these people are smarter than I am. And so I'm just going to soak it up.

• 1:59:37Speaker 01

  And at least half of what I learned at Yale, I learned from other students, right? And the, the first night I'm on campus, you can, you can see what happened. So first of all, I drive from Springfield to New Haven. It's a long drive, but you know, that's how we go places. We, we drive. I get to New Haven and it's, where am I going to park this car? I can't, I, I just thought, of course there'd be, you know, parking lots and they, yeah. And so I find a place in downtown, a garage, and oh my God, this is going to cost me so much money to keep the car here. I, I gotta take it back as soon as I can. And I go up to my, my dorm room in the, in the old campus and I meet my three roommates. And I know how to be sociable, so where'd you go to high school? And two of them tell me they went to prep school.

• 2:00:24Speaker 01

  Huh? What's a prep school? They explain that too. And then they start talking about Phillips Andover versus Phillips Exeter. I don't get what it. And, and, and the third guy, I, I, I won't mention the name, but, but his last name is one of, you know, generational wealth that every American has heard, right? So it's like, okay, I'm, I'm not in the Ozarks anymore. And then they start, you know, smoking dope. And I've never seen that before, right? I've never, I've never, I've never been around people smoking marijuana before. And they assure me, oh, the campus cops, they'll look the other way. And I'm thinking, what? And, and that very summer in Green County where I'm from, a, a judge had sentenced a young man for possession of marijuana, had given him a life sentence.

• 2:01:07Andrew D. Huberman?

  Whoa. For possession of, of weed?

• 2:01:09Speaker 01

  This is 1972 and this is the Ozarks, right? Not, not the same sort of place. So I'm thinking, well, maybe the campus cops would overlook you smoking dope. But I'm not going to give Yale any excuse to send me home. It was like a kid in a candy shop. And because I regarded everyone there as, they certainly knew more than I did, all of them. And, and they were probably smarter than I. It was like, I, I never felt the pressure to be the smartest person in the room. Okay, I'm not, I don't care. And I, I took as many classes as I could. And, you know, I, I always wanted to take six. You were supposed to take no more than five courses per term.

• 2:01:52Speaker 01

  And so I, I would always want to take six and the dean wouldn't let me. So I'd take five courses in, in a lab, which is like half a course, et cetera. And I'm just, you know, I'm not getting nays and everything, but I don't care, right? I didn't fuck. So I'm having a great time. And that's when I learned about neuroscience. So first someone told me, oh, look at this course about comparative psychology. What's comparative psychology? It means comparing across species. And, oh, I didn't know psychologists studied animal behavior. And then pretty soon I, I took a class, Linda Uphouse taught, a physiological psychologist taught neuroscience. And I'm hooked, right? I mean, this is, I love this stuff.

• 2:02:35Andrew D. Huberman?

  It's been a, an amazing arc to go from the Ozarks to Yale. I love that when you found yourself in an environment that offered a lot of opportunity, that you seized that opportunity. I think, um, many people. Wouldn't have done the same had they not had your background, but maybe even if they had. I mean, I think that when you find yourself in a place where there's tons to learn and you throw yourself into that, only good things can come of that. I mean, you mentioned luck, but I think, you know, luck is, I wouldn't say evenly distributed, but it, but it has a habit of finding the prepared, as they say, right? I obviously didn't make that statement. So, and I, and I love this theme of exploration.

• 2:03:20Andrew D. Huberman?

  I mean, we, you know, I think of you as the hormones and sex behavior, hormones and sexual orientation scientist, right? But I also remember, you know, it was 25 years ago that you always walked very quickly and you always had an idea that you were excited about whenever I'd run into you. So I want to say you've really inspired my career to go after things that interested me and, and just really follow those trails. And also when, when it wasn't so clear what to do, to pick the thing that at least was most exciting then and not worry about where that was going to lead next.

• 2:04:00Andrew D. Huberman?

  You strike me as one of the least careerist people I've ever met, like, and I also acknowledge you've had a spectacular career and it's still going. I mean, your name is synonymous with hormones and behavior and hormones and sex behavior. You're being humble now, but it's, it's absolutely true. It didn't hurt that your last name was Breedlove, if I'm honest, but let's face it, that wasn't going to confer you like a real lasting advantage. So clearly you've put in the work. I also really want to thank you for coming here today and, and teaching people what's known about these topics. And these are not easy topics to parse. The languaging has to be very specific. The reason it has to be specific is in one part political, sort of, but it's really about making sure that people understand

• 2:04:45Andrew D. Huberman?

  what's true, what's not true and what's not known yet, so that they can form their own ideas. And, and I really admire the way that you're able to do that. And I also learned a ton today. So, you know, I'm struck by a number of different things in this model of how we become who we are. And as someone who's raised kids successfully and has grandkids. Yes, two. I knew your kids, so that's a trip to me. I haven't seen them in years, but they have kids. I, I think maybe you would just comment briefly on, you know, Did you observe early sex differences in terms of behavior? Was it striking? Did you do experiments on your kids or did you opt not to?

• 2:05:25Speaker 01

  It was pretty amazing, really, now that you mention it. Because Steve Glickman once told me that there was, someone did a study where you ask people, how much do you attribute personality to nature and how much to nurture? And he said, the only correlation that came out of it was the more kids people had, the more they thought nature was important for determining. And you know that because if you have more than one kid, they're not the same. And so, in terms of sex differences, I'll tell you. So I have one daughter, Tessa, and she had two older brothers, et cetera.

• 2:06:05Speaker 01

  And, you know, my partner, Cindy Jordan, neuroscientist too, and she almost never wore dresses, that would be her skirt, that was just, you know, not useful around the lab. And there was a period there where every day with Tessa, it was a struggle if we didn't put her in a dress, right? She really wanted to wear. And as soon as she could walk, one of the things she liked to do was to put on her mother's various shoes, right? And walk around in them. Cute, et cetera. I mean, she was so different from the beginning. Now, I'm not a biological determinist. I don't think, you know, I don't think biology's everything.

• 2:06:50Speaker 01

  I don't think, you know, prenatal things are everything. There's no, there's no one cause of any human behavior. But it, it really struck me. Oh, and, and one of my boys could make a gun out of anything, right? You know, there were trying not to.

• 2:07:05Andrew D. Huberman?

  Even growing up in Berkeley?

• 2:07:07Speaker 01

  Oh, my, well, especially in Berkeley, because he wasn't going to find a toy gun, but by, by golly, he could make one. And, and he was also the, the kid that, that, you know, loved any toy with wheels on it, right? So it was, and, and you know. Even among monkeys, right? Melissa Hines showed it first. Even among monkeys, if you put in wheeled toys, it's the male monkeys that are much more interested in that than the females. And the female monkeys are much more interested in the dolls, et cetera. So, yeah, you have more than one kid. I predict you're going to be amazed about how, you know, how different the kids are, even though you're the same family, right? They don't all come out the same.

• 2:07:49Andrew D. Huberman?

  Once again, you've been a huge inspiration to me over the years. And I know that the listeners are greatly appreciative of everything you've taught. And we got to get you back here. Oh, also, you're writing a book.

• 2:07:59Speaker 01

  Yes.

• 2:07:59Andrew D. Huberman?

  About the biology of sexual orientation.

• 2:08:01Speaker 01

  Yep, I'm trying.

• 2:08:02Andrew D. Huberman?

  We don't do, we actually don't really do book promos. That's not really the, our podcast. But when, when can we expect that book to hit the shelves?

• 2:08:09Speaker 01

  Oh, you've put me in such a tough spot. So I, I'm, I'm struggling with it. I've, I've written six chapters and I'm intending to do 11. My goal is, can I get this first draft done by this fall? And then there, you know, there's reviewing and things like that that happen. So I do, you know, knock on wood. I'm, I'm really hoping I'm going to finish this book. And, and if so, well, you know, I expect you, since you owe me so much, I expect you to buy a copy.

• 2:08:36Andrew D. Huberman?

  Absolutely. I'll buy a copy, I'll read it, and I'll let the world know what I think about it. Dr. Mark Breedlove, thanks for coming here today. Come back again.

• 2:08:43Speaker 01

  It was a pleasure. I've had a great time.

• 2:08:45Andrew D. Huberman?

  Thank you. Thank you for joining me for today's discussion with Dr. Mark Breedlove. To learn more about his work, please see the links in the show note captions. If you're learning from and or enjoying this podcast, please subscribe to our YouTube channel. That's a terrific, zero cost way to support us. In addition, please follow the podcast by clicking the follow button on both Spotify and Apple. And on both Spotify and Apple, you can leave us up to a five star review. And you can now leave us comments at both Spotify and Apple. Please also check out the sponsors mentioned at the beginning and throughout today's episode. That's the best way to support this podcast. If you have questions for me or comments about the podcasts, or guests or topics that you'd like me to consider for the Huberman Lab podcast, please put those in the comments section on YouTube. I do read all the comments.

• 2:09:29Andrew D. Huberman?

  For those of you that haven't heard, I have a new book coming out. It's my very first book. It's entitled Protocols: An Operating Manual for the Human Body. This is a book that I've been working on for more than five years and that's based on more than 30 years of research and experience. And it covers protocols for everything from sleep. To exercise, to stress control, protocols related to focus and motivation. And of course, I provide the scientific substantiation for the protocols that are included. The book is now available by pre-sale at protocolsbook.com. There you can find links to various vendors. You can pick the one that you like best. Again, the book is called Protocols: An Operating Manual for the Human Body. And if you're not already following me on social media, I am Huberman Lab on all social media platforms.

• 2:10:13Andrew D. Huberman?

  So that's Instagram, X, Threads, Facebook, and LinkedIn. And on all those platforms, I discuss science and science-related tools, some of which overlaps with the content of the Huberman Lab podcast, but much of which is distinct from the information on the Huberman Lab podcast. Again, it's Huberman Lab on all social media platforms. And if you haven't already subscribed to our Neural Network newsletter, the Neural Network newsletter is a zero-cost monthly newsletter that includes podcast summaries as well as what we call protocols in the form of one- to-three-page PDFs that cover everything from how to optimize your sleep, how to optimize dopamine, deliberate cold exposure. We have a foundational fitness protocol that covers cardiovascular training and resistance training. All of that is available completely zero cost. You simply go to hubermanlab.com, go to the menu tab in the top-right corner,

• 2:10:58Andrew D. Huberman?

  scroll down to newsletter, and enter your email. And I should emphasize that we do not share your email with anybody. Thank you once again for joining me for today's discussion with Dr. Mark Breedlove. And last, but certainly not least, thank you for your interest in science.

• 2:11:17Speaker 02

  Mr. President, my company formed me of the explosion on our rig

• 2:11:20Speaker 03

  on October 2nd.

• 2:11:22Speaker 02

  Causing massive water displacement and triggering a tsunami. They all heap the blame on me.

• 2:11:26Speaker 03

  Tom Cruise is. Digger got us into this mess, and Digger's gonna dig us up. From the director of Birdman and the Revenant.

• 2:11:34Speaker 02

  What would happen if I stopped drilling? You're stalled, you're freezing there, that's what.

• 2:11:38Speaker 03

  With great power comes great deniability.

• 2:11:41Speaker 02

  I'm not the first daddy.

• 2:11:42Speaker 03

  Digger, see the trailer online. Only appears October 2nd. Rated R, under 17, not admitted without parent.