How long have we been human? (featuring Dr. Scott Solomon)

Daniel and Kelly chat with Dr. Scott Solomon about ancient hominid species, and how we learn about them. See omnystudio.com/listener https://omnystudio.com/listener for privacy information.

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

• 0:00Daniel Whiteson?

  This is an iHeart Podcast. Guaranteed human.

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• 1:13Kelly Weinersmith?

  If I could go back in time to witness any historical moment, going back in time to observe ancient human species would be near the top of my list. How do they build their fires? How do they treat their children? How do they solve problems? And how do they communicate with each other? Do they dance? Do they sing? Do siblings argue with each other? But unfortunately, Daniel hasn't figured out time machines yet, so I'm kind of stuck for now. In the absence of time machines, the best we can do right now is search for fossils and try to learn what we can from things like the shape of these fossils and the DNA that's sometimes left behind. And lucky for us, we have Dr.

• 1:55Kelly Weinersmith?

  Scott Solomon back on the show to tell us about what we've learned so far about ancient hominins. And that's almost as good as a time machine. Welcome to Daniel and Kelly's Extraordinary Universe.

• 2:20Daniel Whiteson?

  Hi, I'm Daniel. I'm a particle physicist, but I don't remember the moment that I became human.

• 2:25Kelly Weinersmith?

  Hello, I am Kelly Weiner-Smith. I study parasites and space, and thank goodness we don't remember the moment we became human. That, I'm guessing that that is a biologically, you know, a private moment between your parents, probably.

• 2:40Daniel Whiteson?

  Oh, I don't know. I don't feel like I was human at birth. You know, I don't feel like I was me at birth. I was just a screaming blob. I think it's fascinating that what emerges from that is a sense of self, a sense of who you are, but you can't really trace it all the way back. Like, its origins itself are sort of lost to your own memory. I feel like that's similar to how, like, as a species, we have some historical memory and some writing, but our own history is lost. But we were there, right? Like, in principle, we saw all this stuff happen. And if we just, like, kept better records, or told each other about it, we would know the answers to all of these questions.

• 3:16Kelly Weinersmith?

  Yeah. Yeah. And I think this is an interesting thread that sort of wove itself throughout our conversation with Scott Solomon, where I think your definition of human encompasses a lot of the things that modern humans do today, whereas I think a lot of us would be comfortable thinking of humans as, you know, like, not too many steps beyond when our, you know, most common ancestor with chimpanzees came down from the trees or something like that.

• 3:41Daniel Whiteson?

  No, I'd love to hold, like, a 1,000-year-old stone tool and think about, like, who was the person who made this? Because there was a person, and they made it, and they, like, had lives and loves, and argued with their siblings, and had betrayals and all sorts of stuff, and maybe even hummed music to themselves, who knows? But, you know, what was it like to be that person? It feels like a real connection with our past.

• 4:05Kelly Weinersmith?

  Yeah.

• 4:05Daniel Whiteson?

  But because we were sloppy in our citations, we don't know who invented the stone tool, and who came up with these early ideas, and who first invented music and stuff. And so unfortunately, we can't give those people credit.

• 4:17Kelly Weinersmith?

  Shame on the early humans. They, why didn't they develop copyright and patent law much earlier? Clearly, that's the peak of humanity.

• 4:26Daniel Whiteson?

  Lab notebooks, man, it's all about lab notebooks. If they had taken better notes, we would know. But don't you find it frustrating? Like, some of the mysteries in the universe, like what's inside a black hole? Like, nobody knows. But these questions, like, where did we come from? How did this all work? People were there, literally. And so somebody knew, we just forgot. It's like, what? What are we even doing?

• 4:48Kelly Weinersmith?

  That is frustrating. And, you know, with black holes, I feel like that's the kind of thing where through equations and good equipment, maybe one day we'll get answers to some of these. But things like, did our hominid ancestors argue with their siblings? Like, gosh, that would be really hard to get an answer for. You know, some of these, like, social things, we're never gonna know. And that, that is a little devastating.

• 5:09Daniel Whiteson?

  Well, the other thing that's frustrating about this whole field is that there are probably answers waiting for us buried in the earth. Like, what fraction of human fossils have we found that exist? You know, some tiny, tiny fraction. And if you just knew where to go, like, oh, go dig here, go dig there, the answers are waiting for you. That's incredibly frustrating in the same way. Like, the answers are there if we could just get them out from the earth. If somebody told me that, like, the answer to what's inside a black hole, I buried it in a treasure chest somewhere on the planet. I would go figure it out. Like, I would be on the hunt, you know?

• 5:44Kelly Weinersmith?

  The rest of your life, you would be spending trying to find that. Yeah.

• 5:48Daniel Whiteson?

  Exactly. And so that, it's so frustrating. These questions are so important and so meaningful. And the evidence is right there in front of us, maybe, but we just can't get to it. Anyway, it's fascinating and wonderful to think about.

• 5:59Kelly Weinersmith?

  Well, and I think it's fascinating and wonderful to be the kind of scientists who are searching for those things, because every once in a while, you do find some amazing piece of information that suggests, you know, this is probably when we started using fire or something like that. And so we are bringing Scott Solomon back on the show. He did an amazing episode in the past about, like, current and continuing human evolution. And now we're bringing him here to look to the past. And he's been to a lot of the archaeological sites where we look at ancient humans. He've researched ancient humans a lot for his upcoming book, where he looks forward to what evolution might look like on Mars. And we had an absolutely fantastic conversation with Scott today.

• 6:37Daniel Whiteson?

  Yes, we did. Thank you, Scott.

• 6:39Kelly Weinersmith?

  And Scott suggested to me that we ask our extraordinaries the philosophical question that Daniel and I have essentially just been discussing, which is, when did we become human? So let's see what the extraordinaries had to say about that.

• 6:53Speaker 04

  I think we became human when we started talking.

• 6:56Speaker 05

  Technically with the emergence of Homo sapiens, but more likely a couple hundred thousand years later, with the development of culture, symbolism, art, and language. Eighty to 100,000 years ago, roughly, when we developed chins.

• 7:09Speaker 06

  Evolution continually progresses. There is no specific enduring definition. By way of example, a person with a substantial set of mutations could be defined as a different species at this particular moment. We cannot truly define when a proto-human became a human and when we change in a way that a particular specimen is no longer a human being by the standard of today. When we got opposable thumbs.

• 7:33Speaker 07

  I think we became human when we came down out of the trees, began to weave leaves for clothing, learned to use fire to cook our foods, lived in communities, and buried our dead.

• 7:43Speaker 05

  Chins and thumbs, amazing.

• 7:45Kelly Weinersmith?

  Yes, we got some fantastic answers. And let's go ahead and see what our expert Scott Solomon says. And so Dr. Scott Solomon is a teaching professor in the Department of Biophysics at Rice University. He's the author of Future Humans: Inside the Science of Our Continuing Evolution. And his upcoming book, Becoming Martian: How Living in Space Will Change Our Bodies and Minds, is coming out through MIT Press in early 2026. He hosts the podcast Wild World with Scott Solomon, taught What Darwin Didn't Know: The Modern Science of Evolution for The Great Courses, and you can check out his streaming series Becoming Martian on Curiosity Stream. Welcome to the show, Scott.

• 8:27Speaker 05

  Thank you. I'm excited to be back. Thanks for joining us to talk about humanity. Let's do it.

• 8:32Kelly Weinersmith?

  Yes, we're so glad you're back. We had so many good comments from the last episode that you were on, talking about evolution. I think our community doesn't get enough evolution, and they're excited to hear about it. So let's talk about Homo species. So did a lot of ancient humans exist previously? And like, how do we know about how many of them there were? Like, do we think there were a lot of them?

• 8:52Speaker 05

  Yeah, that's a really good question. So, you know, I guess what we're talking about is, you know, species that existed once upon a time that are not our species, Homo sapiens. That are also, you know, close relatives, maybe not in a direct line of dissent to us necessarily. That's kind of an interesting thing to talk about, but we know, for example, that we shared a common ancestor with chimpanzees. Chimpanzees are among all the species that are still alive today. They are our closest living relatives. And we know that because mostly of genetic data. So we can look at the DNA of chimpanzees and all of the other apes and primates and everything else that's alive.

• 9:35Speaker 05

  Compare it with our own DNA and they're actually more closely related to us than they are even to other apes like gorillas, which that part alone kind of always blows my mind. I think it's incredible, right? You think about chimps and gorillas as being kind of like similar to each other, but chimps are closer to us than to, you know, any other living ape other than us.

• 9:54Daniel Whiteson?

  And that's a measure where we just are looking at our DNA and looking at their DNA and calculating some sort of genetic distance. Is that right?

• 10:00Speaker 05

  That's part of it. It's actually even more complex than that. It's kind of cool because, you know, you can just look at like, what percent similarity do we have? And that's one measure of it.

• 10:09Daniel Whiteson?

  Though that measure is weird because we also have like 50% DNA in common with bananas, right?

• 10:13Speaker 05

  Exactly. That's right. Well, we do share a common ancestor with bananas, but you have to go back pretty far.

• 10:20Speaker 05

  So yeah, I mean, that's telling us about common ancestry, right? It's telling us about, it's like you have some percent of your DNA in common with your cousin and even less in common with your like, you know, fourth cousin twice removed or whatever it is, right? So yeah, if you go back far enough, you can find DNA that we have in common, even with like bacteria. There's not much, but there's a tiny bit. So the more that we have in common, the more closely related we are in general. But even more specifically, it gets down to like, yeah, but what DNA? What's the DNA doing? And that's when it gets really interesting because then we can actually trace the history of specific genes and see the way that those genes have changed over time.

• 10:59Speaker 05

  And that allows us to put together kind of a family tree of similarities and track exactly how those parts of our genome have changed over time. So we now know that if it, if you went back in time about six to seven million years ago, you would find the common ancestor that we shared with chimpanzees, right?

• 11:20Daniel Whiteson?

  Six or seven million. Nice.

• 11:23Speaker 05

  Six or seven million. So, you know, like, you know, I have friends who are historians and we always joke about like, to me, that's like yesterday, right? Like six to seven million years. That's not so long ago for an evolutionary biologist or geologists also, you know, they would kind of probably be on the same page with that. Like, oh yeah, it's yesterday and, and, you know, in the history, you know, if you're used to time scales on the order of hundreds or thousands of years, that's, that's a long time ago. And that's, and that's fair.

• 11:49Daniel Whiteson?

  Well, my experiments take 10 to the minus 23 seconds. So six million years feels like a long time.

• 11:56Speaker 05

  But not in the history of the universe, right? I mean, that's like, that's like a blink of an eye.

• 12:00Daniel Whiteson?

  Yeah, absolutely. So you're saying that we have a common ancestor with chimps and we know that because we've looked at the DNA and we can project back based on the rate of change and the specific genes that have changed. Have we found a fossil that confirms that? Or is this just based on DNA?

• 12:16Speaker 05

  Right. That's great. It's a great question. So yeah, so we do know a lot about the history of the lineage. Like if you think about that split between, so there's a common ancestor of humans and chimpanzees. And then there was some kind of a split that took place. And there was one lineage that eventually led to chimpanzees and another lineage that eventually led to us. And we can talk all about what do we know about that? But your question is like, do we have fossils to help to fill in the picture of what was happening at the time of the common ancestor and maybe right afterwards, right? To help complement what we know from genetics. And the answer is sort of. We do have fossils that go back to around that time. It turns out that that period of time in the part of the world where

• 13:00Speaker 05

  this was happening, which was like tropical Africa, doesn't unfortunately have a ton of great fossils preserved from exactly that time. So that's one of those things where there are some kind of missing little gaps in there. But we've filled in more and more and more. And so we are starting to get a really much more complete picture of not only what was happening around that time, but particularly of all the things that happened subsequently. Like if you track the lineage that eventually led to us, turns out it's way more complicated than people used to think, right? So, I mean, you can go back to Darwin's time, right? Darwin, he

• 13:41Speaker 05

  Obviously, you know, gave us the the first notion that we have this evolutionary history, right? And he speculated that we must be closely related to the great apes, the chimpanzees, gorillas, orangutans. And that was based just on like similar anatomy. Like if you look at the skeleton of a chimp and a gorilla and a human in a museum or something like that, like, you know, there's a lot of similarities. There's some pretty clear differences, too. But he speculated that they must be our closest living relatives. And then he also speculated that there must be some fossil species that once existed that kind of spanned that gap between us and the common ancestor that we shared with

• 14:26Speaker 05

  those apes. And he even predicted that that common ancestor probably lived somewhere in Africa, mainly because that's where the majority of apes, great apes, that's chimpanzees, gorillas, orangutans. So there's orangutans in Asia, but gorillas and chimps are only in Africa. So that kind of makes you think, okay, Africa might be where most of this history took place. But at the time, none of those fossils were known. So that was really just kind of like a, kind of a wild guess. And it took a while, but he turned out to be right.

• 14:59Kelly Weinersmith?

  I'd like to talk about how fossils are formed, but right now, so, okay, so I'm thinking of a V in my head. And the bottom of the V has our common ancestor, one side has chimpanzees and one side has Homo sapiens, which is us. And we've talked about how there are other Homo species also. What's the right way to think about where those lines belong on this V that I have in my head?

• 15:21Speaker 05

  Yeah, so if you think about that V, you're right, like the the point where the two lines come together, that was the common ancestor that we we shared with chimpanzees. Something happened and there was a split. And then the lineage that eventually led to Homo sapiens, this is where like, I think a lot of people have in their mind that like image of like a hunched over ape that like, then there's like slightly standing up a little taller and then a little taller and eventually like leads to to us and then like-

• 15:47Kelly Weinersmith?

  It's on the shirts, so it's true.

• 15:49Speaker 05

  Yeah, exactly. Or the bumper stickers or the memes and then like often, you know, like the next step is like, you know, hunched over a computer or some or, you know, some insert joke here, right? Like about the downfall of humanity, however you however you perceive it. But but that idea is like, okay, we we the common ancestor that we share with chimpanzees. We think actually looked, it wasn't a chimp, but we think it would have looked more chimp-like than human-like. That's, I think that's a fair statement to make. Like, you know, getting back to the question about, do we have fossils? We have fossils from very close to that time that do look much more chimp-like than human-like. And what I mean by that is if you look at the structure of their bodies, you know,

• 16:33Speaker 05

  one of the big differences between chimps and us is chimpanzees, they don't walk on two feet. They actually can walk on two feet technically. If you give chimpanzees two very good pieces of food, like two bananas or something like that, they will hold one in one hand, one in the other hand. And then if you want to get away from the other chimps, you gotta, you gotta move and you gotta walk upright on two. So they'll do it, but they look super goofy. And the reason is actually interesting. It's because they can't balance on one foot. So like, you know, if you're sober, you might be able to balance on one foot pretty effectively, right? That's because our hips and our leg bones and our spine and, and our foot, you know, all of that is structured in such a way that enables us to walk

• 17:17Speaker 05

  in a way that like, for a brief moment, you are kind of balancing on just one foot while the other foot is moving forward. And for a chimp, they have to lean all the way to one side in order to not fall over when they do that. So they look really goofy because their kind of bodies moving left and right to, to not fall over. It's not a very effective way of getting around. And so, you know, most of the time what they do is that what's called knuckle walking. They walk on all fours, but rather than like putting their hands palm down on the ground, they, they put their knuckles down in a way that looks super uncomfortable to me. Like I would never want to walk around. Like I don't think any toddlers are crawling around with knuckle walking that I've seen. But,

• 17:59Speaker 05

  you know, it's, it's an effective way for, for chimps and gorillas to get around.

• 18:04Daniel Whiteson?

  All right. I have lots of questions about chimps and growing bananas and knuckle walking, but I want to hear the answer to Kelly's question, which is about where those splits happen. So after the split between the chimps and the proto-humans, are there lots more splits? How do we think about that?

• 18:18Speaker 05

  Yeah. So basically after the split, With, you know, the chimp lineage. So those very first species that are on the, on our side, on the human side of that split, they would have been walking on their knuckles just the same way that, that chimpanzees and gorillas do. They weren't really able to walk upright yet. But that starts to happen in the fossil record. So you start to see species that are around five to six million years old that have some of the anatomical features that we use for walking upright in their, in their pelvis, their hips, in their spine, in their, their legs, right? And there's a lot of things that you don't necessarily think about that are associated with walking upright. Even like where your, your neck, the bones in your neck,

• 19:02Speaker 05

  attached to your skull. For us, it's like the bottom of the skull. But if you look at like a dog or another four-legged animal, it's behind the skull. So that has to change. There's a lot of anatomical changes that take place to be able to walk upright. And what's really cool in the fossil record is we start to see some of those individual components popping up in these species that are from around that, you know, five to six million year old range. But then you get more splits, right? So what's really, I think, one of the most fascinating aspects of what we now know about human evolution is it wasn't a straight line. You don't have this kind of like, you know, one species that was hunched over leads to one that was a little more upright

• 19:44Speaker 05

  to another is a little more upright. They kept having more and more events where there was like one species that split into two, more of those Vs. And so what we actually see is a whole bunch of different species that are on the human side of the split, but are not necessarily species that ultimately left any descendants. They don't necessarily lead directly to us, but they were more closely related to us than they were to chimpanzees.

• 20:15Daniel Whiteson?

  And when we talk about these splits, it's a nice sort of diagram to have in your head. There's a solid line. It splits as another solid line. But in reality, on the ground, you're talking about populations. Those populations are drifting apart. And so that speciation event takes a little bit of time, right? You have like. Which start to differ and then diverge and then at some point they can't make babies together anymore and that's when you say they split, right? It's a bit fuzzier than the cartoon lines we're drawing in our minds, right?

• 20:40Speaker 05

  No, that's exactly right. It is a process and we can only sort of see it as a process that played out as one lineage that led to two, only after a lot of time has passed. And actually, we know that sometimes you can start to have a split, but then they might come back together and sort of like reform. So speciation started to happen, but doesn't actually go all the way through to completion.

• 21:01Daniel Whiteson?

  They argued about bananas, then they got together and decided to share the bananas.

• 21:05Speaker 05

  That's right. There, there seems to have been a lot of sharing of bananas in the, in the history of our, of our distant relatives.

• 21:13Kelly Weinersmith?

  Bananas are showing up in this show more than I would have guessed.

• 21:16Daniel Whiteson?

  It's human evolution. Of course, we're gonna go bananas.

• 21:18Kelly Weinersmith?

  Ah, love it.

• 21:20Daniel Whiteson?

  So I love this conversation because we keep coming up with more and more questions to ask, but I think that finally gives us a chance to unwind back to our original first question, which was, were there lots of other homo species previously? How many do we need to think about as we're tracking the development of the population that would eventually birth us?

• 21:37Speaker 05

  Yeah. So we now think that there were something like 20 species, maybe more that, that existed between the common ancestor that we shared with chimpanzees and our species, Homo sapiens. Now, the exact number is something that the scientists that study human evolution like to argue about a lot. That's a very contentious, so exactly where to draw those lines between species gets complicated. And partially that has to do with what you were saying, Daniel, about like, the process of speciation isn't always clean. It can be a messy process. And so sometimes it's like, well, is that really a different species? Maybe that was like, something that started to become different, but maybe didn't proceed

• 22:19Speaker 05

  all the way to what we would normally consider to be a new species. That could explain part of it. And the other part of it is like, any species you look at, you know, there's always variation. Like, these guys over there look a little different. These ones over here have an interesting weird behavior that's different. Any species, right, that you look at. So that always makes it a little messier when you try to say like, Where do we draw the boundaries around the edge of what is a species?

• 22:45Daniel Whiteson?

  And just to clarify, when you say 20, do you mean there's like 20 steps along that line between the split between chimps and us? Or do you mean there are 20 sort of parallel tracks there where different kinds of homo species split off?

• 22:58Speaker 05

  Yeah, exactly. It's the latter. So it's not, it's not the case that there was a stepwise sequence of A led to B, B led to C, C led to D, and count them all up and there's 20. It's more of picturing like a bush, right? So you've got like one stem and you can trace that that stem branch is off and you get two more leaves over there. But then on another branch, just over here, there's, you know, there's three stems and they each have three leaves. So some of these species were living actually at the same time. And that gets to be really intriguing to think about.

• 23:31Daniel Whiteson?

  The banana politics were bananas.

• 23:35Kelly Weinersmith?

  So you said we have maybe 20 species, which I'm guessing that number must have arisen from a bunch of fossils that we found. Do you think we'll be arguing over these same 20 forever? Or do you think there's a lot of additional homo fossils out there that we haven't found yet? And maybe we'll end up saying there's like 100 homo species?

• 23:53Speaker 05

  Yeah, it's a good question. I mean, I think two things have been happening in the last few decades, both of which are super exciting. One is that like we keep finding new species of, of, you know, I'm going to say hominids. Hominid is the term that we use to describe anything on our side of the split from chimpanzees, right? So they're not all in the genus homo. We get to the genus homo at some point in that history, but that's a relatively recent development. There were other types of hominids that were in different genera, like Australopithecus is another one. So folks might be familiar with Lucy. That was a species known as Australopithecus afferensis. And that is another example of a hominid. So more on our, it's definitely on our side of that split.

• 24:39Speaker 05

  But not in the genus Homo. So of all of those, if you add them all up, then you can get something like 20. And so, like I said, there's, you know, new discoveries that keep happening of new species, some of which are in the genus Homo, some of which are in some of these other hominid genera. So that keeps happening and that's, of course, super exciting because these are, you know, helping fill in the, the, the full story. But the other thing that keeps happening is we keep finding more and more examples of things that we already knew about. And one of the things that that has been doing is helping us to recognize that sometimes these two things that we thought were different, if you find something kind of intermediate in between them, you start to sort of get a fuller picture and recognize, maybe this

• 25:22Speaker 05

  is actually all one thing and maybe we need to, you know, not be always splitting everything up, but maybe sort of, you know, we talk about lumpers and splitters in, in, in the science of taxonomy and people tend to, you know, be more along the lines of kind of, oh, every difference I see, I'm going to call a new species. Those are, we call those splitters and the lumpers are those that say, well, there's variation within a species. We can lump all these together into, into one. And it's always a back and forth and the reality is often somewhere in between. But yeah, both of those things are happening right now and that, like I said, it's super exciting, but it also means it's hard to predict where we're going to end up in terms of like, how many species might there end up being? Yeah, I don't know.

• 26:04Kelly Weinersmith?

  You're doing such a good job of explaining this stuff, Scott. I love hearing you talk about humans. All right, we're going to take a break and when we come back, we're going to hear more about how we go ahead and study hominids.

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• 28:11Kelly Weinersmith?

  And we're back. Scott was telling us that there's maybe 20 hominids, but who knows where that number is going to be in the next decades. So let's go ahead and talk about how we study these. So first of all, you know, you mentioned that a lot of these species are found in Africa, but that there's not a lot of fossils. Like, what kind of conditions do you need to get a fossil in the first place?

• 28:32Speaker 05

  Yeah, I mean, when you think about what has to happen for a fossil to be not only formed, but also like found, it's kind of amazing that we have any. I mean, first of all, like when something dies, right? A lot of times what happens is it gets eaten, it gets chewed up, it gets, you know, broken down, destroyed in some way, either immediately upon death. I mean, if something gets eaten, right? You know, if you go to East Africa today and go on a safari and you see the, the big animals, there's big predators and, you know, scavengers that live out there. It's amazing that any bones have made it at all up until today. So first of all, when that individual died, it had to not have its bones destroyed.

• 29:15Speaker 05

  But then later, something had to preserve them. So one of the places that I've been very fortunate to, to spend some time is a place in Tanzania called Olduvai Gorge. And this is a very famous site in the history of like our study of human evolution, because a lot of hominid fossils have been found there. And I co-teach a field course there with my colleague here at Rice University, Manuel Dominguez Rodrigo, and he oversees excavations of fossils at Oldenby Gorge. So we take students there and, you know, it's incredible because you walk around and in this one particular gorge, it's like a canyon, right?

• 29:57Speaker 05

  There's literally fossils just strewn about on the ground. Wow. And so it's a perfect example of like how if you get the ideal conditions, fossils can actually be common. This is one of the few places in the world where the conditions were really ideal. And what I mean by that is, first of all, it was a place where a lot of animals and hominids, it turns out, gathered together. And the reason is that between, you know, about 1.8 million years ago and a million or so years ago, this area was a, it was a lake. It was a shallow lake. And so, of course, like a water hole, we all know that's a good place to go to find wildlife and, you know, hominids would have gone there for water as well and maybe also for hunting, it turns out.

• 30:42Speaker 05

  So there's a lot of species there. And then when those individuals died, it turns out that the second thing that is ideal about it is that there are these volcanoes nearby and these volcanoes will spew out ash periodically when they erupt. And that ash can bury all of the things in the area, including the bodies of anything that had recently died. And that then can basically preserve them. And basically what happens is they go through a process in which all of the kind of organic, all the carbon-based, you know, chemicals in our body get gradually converted into minerals, basically into rock, right? And that's what a fossil is.

• 31:27Speaker 05

  It's a, it's a rock that has the same, you know, shape as, as bone or other structures. And so you had the perfect conditions for preserving all of this there. And then the third thing, which is really remarkable, is that now you have today a river running through that area. And of course, that caused erosion. And then the erosion means that the layers that have the fossils are actually exposed at the surface. Wow. So all of those things kind of all have to take place in order for a fossil to not only be formed, but also to be accessible.

• 32:01Daniel Whiteson?

  Why can't we develop some sort of technology that looks into the ground to see if there's a fossil there?

• 32:06Speaker 05

  Yeah, I know. I was telling my colleague Manuel Dominguez Rodrigo, every time I'm in the field with him, I'm just so amazed by how patient he and his team are because they're showing us all of the ways that they do these excavations. They're so meticulous and careful, documenting every millimeter, literally. And then they're slowly chipping away at the edge of this canyon. And we're looking at the canyon. I'm going like, Manuel, what's in there? Like, aren't you dying to find out what's in there? And he's like, I mean, yeah, of course. Like, I don't know how you avoid the temptation to just kind of hack away at it. But we know that you have to be careful when you do these excavations.

• 32:44Daniel Whiteson?

  Well, actually, let's put a finer point on that because this is something that I see people misunderstanding online, when they're impatient about excavations all over the place. Why do you have to be so careful? Why can't you just take a bulldozer and find a bunch of cool fossils?

• 32:57Speaker 05

  Actually, it's a really good point to discuss because there have been times in the past when that is what people have done. And there still are certain situations in which people still do that today. The problem is, sure, you might find, well, first of all, you might destroy the fossils in the process of excavating. That's a real risk.

• 33:13Daniel Whiteson?

  Yeah.

• 33:14Speaker 05

  But the second thing is, even if you find them, a lot of what we can learn about a fossil comes from the exact situation in which it was found. So you can hand me a fossil bone, and I might be able to like, tell you some things about it, or more to the point, I can hand it to Manuel, and he will tell you some things about it. But we can get a lot more information by saying, oh, yeah, but this fossil was found together with maybe this stone tool, or with these other fossils, or maybe there were multiple individuals together in this place. That starts to tell us something about the like, social interaction. Actions among these individuals and they've literally found carcasses of animals with stone tool cut marks on the bones and the stone tools are still there like it just it's insane.

• 33:59Speaker 05

  Right. So you can learn so much about what people or hominids were doing at the time by understanding the exact context in which these were found. So if you destroy that, you've lost the opportunity to learn anything that we can learn.

• 34:14Daniel Whiteson?

  And if you rush through your excavation, then you're sort of using it up for future generations where people might develop better technology, less invasive, or understand there's questions that they want to ask that we can no longer ask because people excavated using technique X instead of technique Y.

• 34:30Speaker 05

  Yeah. And that's actually something that, you know, archaeologists and paleontologists today recognize and part of their sort of standard practice is to always keep a section that is not excavated and think that might be really interesting, but to preserve it for future generations under the assumption, as you said, that like at some point in the future, people are going to have other ways of studying this that we don't have today and we don't want to, you know, cause them to miss out on that opportunity.

• 34:56Daniel Whiteson?

  So why can't we like put a thumper on the surface and like gather a bunch of data and feed it into AI and have it tell us like here are all the fossils?

• 35:04Speaker 05

  Yeah. So I think there have been some developments along those lines. They can use things like ground penetrating radar to like look underground and try to get some sense of what's there. And you might be able to find some large things that way, but to find, you know, some of the fossils that that they pull out of these sites are incredibly tiny. And so, you know, I think part of it is, is just the resolution of these technologies. And the other thing I think is that, you know, keep in mind, the fossil is rock.

• 35:31Daniel Whiteson?

  Yeah.

• 35:31Speaker 05

  And you're looking for one rock embedded within a bunch of other rocks. So like, you know, I don't know much about the specifics of how the technology works, but I'm guessing that just being able to differentiate between those two types of things is probably really hard.

• 35:44Kelly Weinersmith?

  Yeah.

• 35:44Daniel Whiteson?

  You're looking for a needle in a needle stack.

• 35:46Speaker 05

  Basically.

• 35:47Kelly Weinersmith?

  How many hominid species has Manuel found in there?

• 35:50Speaker 05

  Well, they have found a few, but you know, in Old Devi Gorge generally, there are three species that are known from the fossil record from that particular site. And it's actually the place where two of them were first discovered. So the very first hominid fossil found at Old Devi Gorge was found by Mary Leakey, along with her husband Louis Leakey. They were sort of the pioneers of looking for human hominid fossils in that site. And they found one that they called Zinj, Z-I-N-J was the nickname. It was short for Zinjanthropus boisei is the species. And the genus name has been revised since those days. It's now known as Paranthropus boisei. But that was a really big deal.

• 36:32Speaker 05

  And that's a good example of a hominid that we think was on a branch that didn't eventually lead to us. There's, you know, like I said, there's debate among folks in this field about exactly what the, the shape of that family tree looked like and which species led to which other species, et cetera. But they were pretty different from us. They were more sort of like large bodied, very thick jaw. They looked like they were eating like grasses or other very like fibrous foods that are really hard to break down. So their skull is quite different from the species that we think are the ones that eventually led to us. Another species that was first found in Old Devi Gorge is Homo habilis.

• 37:14Speaker 05

  So this is now in the genus Homo, right? And so this is something that is certainly more close to Homo sapiens, but still, still pretty distinct from us. And in part, it's based on like the size of the head, which of course is, you know, an indication of the size of the brain. So we talked before about like walking upright being one of the big transitions that took place. The other major one, I mean, there were a lot, but the other major one was the expansion of the brain and therefore the expansion of the skull. And so in part, our genus Homo is defined by the size of the skull. But we also see within species of Homo, kind of more and more expansion of the brain, which, you know, is at least correlated with intelligence.

• 37:58Speaker 05

  Intelligence is famously hard to, hard to define, hard to measure. It's not, you know, brain size isn't a perfect measurement of intelligence by any means. But at least in looking at the history of human evolution, we do think that with a larger brain, you know, generally speaking, you start to see more intelligence and more sophisticated types of behaviors.

• 38:18Daniel Whiteson?

  It is amazing that we have any fossils, given how hard it is to arrange all those things to happen just the right way. Don't you worry that you're looking at an unusual, unrepresentative sample of the ancient population because you know that it doesn't happen evenly everywhere? For example, if future humans only studied like current physics professors, I wouldn't want them to extrapolate, you know, the whole population based on a few of us. Don't you worry about that? And how big a sample are we talking about? Like, how many different individuals have we found fossils of?

• 38:49Speaker 05

  Yeah, that's a really good point. So you've got the small sample size problem. Anytime you're dealing with fossils, right? You're gonna, like I said, it's so hard to, you know, even have them be preserved, much less find them. So what often happens is, you know, somebody finds something and it's the first of that kind, right? And then that makes it hard to draw too many conclusions because we don't know, you know, how representative it was. But what has fortunately happened in the last, I would say, you know, sort of 50 years or so, especially in the last few decades, is we've found more and more examples of the same, what people generally accept as being the same species. And like I said, there's some debate about, is this the same? Is this not? Where do you draw the line? But there's some exceptions.

• 39:33Speaker 05

  Some of the earliest species are only known from a few specimens. But as you get more and more recent, as you get to something like, for example, Homo erectus, that's a really interesting species because we know that the earliest Homo erectus were found in Africa. But then you start to see Homo erectus popping up in the Middle East, in parts of Europe, and in parts of Asia and Southeast Asia. In fact, the first one was found on the island of Java, in what is today Indonesia. So that was the very first member of our lineage, the very first hominid, to leave Africa and spread out across a lot of the world. So there's a lot now of fossils of Homo erectus.

• 40:12Daniel Whiteson?

  Is that like 100, or 1,000, a million? How many are we talking about?

• 40:16Speaker 05

  Not a million. I don't know the exact count, but I would, I would hazard a guess that we're talking about, you know, hundreds, something like that. Yeah. And, you know, some of these are very fragmentary, so you might only have one bone, right? And in other cases, you'll have part of a skull. But kind of putting it all together, we have a very good sense of what the entire body looked like. That's the other thing, right? Is like, you might only have a tiny piece of something and you have to figure out how much information can you get about the entire? Individual, much less the entire species from that one little fragment. In some cases, we can learn a lot, but you know, it certainly helps to have more and more pieces of that puzzle.

• 40:56Kelly Weinersmith?

  Can we talk about timeframe a little? So I think you said that the split between chimpanzees and humans was like six to seven million years ago. And then you were talking about Manuel's study site. And I never remember the name of the place, so I'm just going to say Manuel's study site. That was 1 million to 1.8 million years ago. What is the like earliest date when there were other hominids around? And this question's going to lead into whether or not we can get DNA out of any of these.

• 41:22Speaker 05

  Yeah, yeah, that's really important question. So, yeah, so, yeah. You know, you start to see, let's see, I think Lucy's species, that's Australopithecus afferensis, is around three and a half million years ago. So there you have an example of a species that is definitely walking upright on two feet, very much like us. We even have footprints. This is incredible. There's a site in Tanzania, near Old Evi Gorge, where there are preserved footprints where, I mean, it really is like basically like perfect conditions. The volcano, one of those volcanoes erupted. There was ash all over the ground and then it rained. So then you have like a wet cement situation.

• 42:02Speaker 05

  And then some of these individuals walked through that area and the ash hardened and then that was preserved. So we could actually retrace their exact gait. You know, the kind of like, if you go to get fitted for like running shoes or something, they'll go and they'll like analyze your gait, like how long are your strides? Where are you kind of putting pressure on your foot? And they'll give you the right shoe to kind of help with your specific gait. They can do those types of reconstructions on the gait of Australopithecus afferensis at three and a half million years ago because of these tracks.

• 42:35Daniel Whiteson?

  Incredible.

• 42:36Kelly Weinersmith?

  So cool.

• 42:37Daniel Whiteson?

  Can they tell if they had to like drag a screaming toddler along or something?

• 42:40Speaker 05

  Well, actually, so there is.

• 42:43Daniel Whiteson?

  Prehistoric Cheerios were dropped.

• 42:44Speaker 05

  There is an indication of older individuals and younger individuals in some cases. And we have now also found fossils of individuals of different ages for some of these species. So we're starting to fill. A little bit of what the kind of, you know, what does a childhood look like for Homo erectus and things like that? But, you know, the other thing I was going to say is, so for that species, for Lucy's species, Australopithecus afferensis, they're walking upright like us, but they didn't have a big brain like us yet. So we're starting to sort of see pieces that we know walking upright happened first. So by three and a half million years ago, you had people walking around in much the same way that we walk around. But they didn't have a brain nearly the size of ours. It was more of a chimpanzee sized brain.

• 43:24Speaker 05

  So we assume that means most aspects of complex human behavior, language, art, social, you know, dynamics, wouldn't have yet been in place. Now, there's a lot of, you know, guesswork that has to be done. But that's, that's the best guess for that. So you don't get the, you know, the, the very enlarged brain happening until just the last couple of million years. And it's, it keeps increasing over the last two million years. And this is super interesting because you also want to know, well, why? Why did we become more intelligent at this particular time? Right?

• 44:03Speaker 05

  And one of the things that is fascinating is that the time at which our brains started to really shoot up in size coincides with the time in which the climate in East Africa was very volatile. Like it was, you know, swinging wildly from, you know, hot and wet to cold and dry. And it kept changing in a much faster way than it had previously. And so there's this idea that those wild fluctuations in climate led to uncertainty, right? And you had to kind of keep adapting, adjusting, but maybe in a way that evolution itself can't keep up with. Right? So you can't adapt through natural selection when the environment is constantly changing.

• 44:45Speaker 05

  Rather, maybe a better way to do it is to develop intelligence that allows you to be more adaptable yourself, to be able to use your intelligence to work together as a cooperative society to try to solve problems like finding food, finding water, protecting yourself from enemies. So there's this idea that that climate being kind of going through these wild changes might have driven the intelligence of our ancestors.

• 45:13Kelly Weinersmith?

  So that leads nicely into a question we have from listener Jesse. And so here's the question. If there is a physical and/or sociological advantage to becoming an upright tool using intelligent species, would the same advantages apply to the rise of an intelligent alien species on another habitable planet? And if physical characteristics are essential for becoming an intelligent species, must they then be more human-like? Surely, we could have limbs grown out of our heads or otherwise. Okay, so I feel like that kind of ties into what is needed to become an intelligent species. And this is also a question for Daniel, who thinks a lot about aliens.

• 45:50Speaker 05

  Well, you know, I love this question for a lot of reasons. One of which is I'm teaching a class right now on astrobiology and we're asking exactly these kinds of questions and talking about them with our students. Like, how much can we use the history of life on Earth to think about what might have already happened on other planets and to think about what could happen in the future on other planets and other worlds and different lineages of life? And so, you know, I think there is this idea, at least, that some species on Earth would have become as intelligent as we are. That's one way of thinking about it, that like, it happened to be us because, you know, the asteroid hit the Earth and killed the dinosaurs and it ended up being mammals, but

• 46:33Speaker 05

  maybe we could have had a super intelligent dinosaur slash bird or something like that. That's like one argument that has been made, that like, somebody was going to become super smart and it happened to be us. There's another argument that like, it doesn't have to happen at all and the conditions had to really just be just right. And in that way of thinking about it, you know, we happen to be at the right place at the right time and have the right kind of combination of traits already in existence that allowed us to sort of evolve through natural selection to be able to, you know, basically solve problems in one particular way.

• 47:14Speaker 05

  And that way appears to have been through the use of language and collective problem solving and social, you know, complex social interactions that we know how to manage. And that's kind of a uniquely human way of solving the problems of, you know, adjusting to this extreme environment. So, you know, I tend to kind of lean more that way, that like, we got lucky, you know, like, it didn't have to happen this way. And While, you know, that has implications for understanding our origins, I also do think it has implications for thinking about what could happen elsewhere, right? So it doesn't necessarily mean that there has to be intelligent life elsewhere.

• 47:54Speaker 05

  But maybe if the conditions are just right and there are species elsewhere that happen to have the conditions that are necessary and be at the right place in the right time, then that might happen for them too.

• 48:07Daniel Whiteson?

  I think it's really important to try to tell these stories and try to understand our history. But something I struggle with is knowing how to test these ideas. Like, it sounds compelling, but you know, there could be another idea that explains that there could be another factor. Usually in science, you don't just tell a compelling story that describes your data, you try to predict something that happens and say, well, here's a prediction I can use to test this theory versus that theory. Are aliens the way we can do that? You build a model for how intelligence develops and then you can apply it to some new data set where you're like, I predict intelligence on this planet, or I predict no intelligence on this planet. Or is this just an impossible standard because we're talking about things in the deep past and things that move very slowly?

• 48:46Speaker 05

  Yeah, no, I think it's a really good, really good point. And you're right that we always want to be able to back up our assertions with, with data. And so otherwise, it's a nice story, but you know, there's no way to know that that's the correct interpretation. So one of the problems we have with the study of human evolution is that, as far as we know, it only happened once. And so, you know, even if we could reconstruct the exact sequence of events that led to us, it still doesn't tell us how generalizable that is. It still doesn't tell us how likely it was to. We can say that it did happen, but we can't necessarily know, well, if you change X, Y, and Z, would it have played out that same way again? So, I mean, there are ways to do simulations, right?

• 49:28Speaker 05

  There are ways to run experiments with, with other organisms, you know, that aren't humans that we can try to recreate certain conditions, but it's not quite the same. So I think part of this is the inherent problem we have of, you know, human evolution happened once, there's only one lineage of hominids. Although, if there were multiple species living in the same place, that does allow us to ask some questions about the differences that existed between them. And, you know, maybe someday we'll know why our lineage is the one that survived and not any of the others that very well could have.

• 50:03Kelly Weinersmith?

  All right, let's take a break and when we get back, we'll take a question from Alberto about whether or not our hominid species has, let's say, mixed our genetic information with some of the other hominid species in our early history.

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• 52:11Kelly Weinersmith?

  And we're back. And let's start with a question from Alberto. All right, so Alberto asked, I recently learned about another hominid branch called Denisovans. Would you be willing to share more information about them? Are there modern humans that share their DNA? And I'll add, I think Neanderthals, we also share some DNA with them. So yeah, tell us about our species doing the hanky panky with some others.

• 52:33Speaker 05

  Yeah, I mean, this is one example of some of the just absolutely incredible work that has happened in the last few decades. That's really kind of given us a much, much more complete picture of our ancestors and how we got here, but also like a much, much more, I would say, interesting, a much more complex version of the story. So yeah, so what happened with the Denisovans? This is a discovery that took place in 2008 in a cave called Denisova Cave in the Altai Mountains of Siberia. And what was found was a part of a finger and a tooth. So not, not much, not much to go by. But because this cave is a place that is pretty cold and dry,

• 53:16Speaker 05

  that turns out to be pretty good for preserving DNA. And in this case, they were able to actually extract and sequence the entire genome of the individual that was found, just based on this tiny little fragment of bone and teeth.

• 53:31Daniel Whiteson?

  So this is bone and teeth, not fossils, just to be clear.

• 53:34Speaker 05

  So it was in a state that was, I guess, partially fossilized. And so there was still organic material in there. And so they were able to actually get enough of it. And, you know, part of what happens with looking at ancient DNA is you can still have some DNA present, but if it's broken up enough, if it's degraded enough, then you can't necessarily make much sense out of it. So this was both preserved and intact enough for them to actually sequence the entire genome. That was published in 2010. And basically, what they determined is that this is a new type of hominid. And they were similar to Neanderthals.

• 54:15Speaker 05

  Because we also have DNA, in fact, complete genomes from Neanderthals that had already been published. And so this is basically a branch of our family tree that is similar to Neanderthals and yet distinct enough that they're kind of considered a separate type of hominid. And I'm not using the term species because there's debates about is it actually a different species? Is it, you know, the same species as us? What we do know is by looking at the DNA of these Denisovans is that we actually still have some of the DNA from Denisovans in people living today. And so, yes, we know that our ancestors, I

• 54:58Speaker 05

  say us as Homo sapiens, modern humans, that at some point in the past, and actually, we now know this happened multiple times in the past, that there were episodes in which our ancestors, Homo sapiens, mated and had children with Denisovans. And not only that, but that that led to a child and that child was, you know, cared for and nurtured and survived itself to be an adult and to go on and have its own kids. So I think it's useful to point that out, right? It's not just, people talk about, oh, we mated with, you know, Denisovans. Yes, and had kids with them. And those kids were, you know, presumably

• 55:40Speaker 05

  loved, right? I mean, we all know that that kids require a lot of care, certainly when they're young. And so, so somebody, you know, cared enough for those kids to nurture them and they survived. And eventually, some of their genes have ended up in us. So it's not a lot of their genes. So the the highest percentages are like 5% Denisovan. So you can have individuals alive today who like 5% of their genes. So these are like the parts of our genome that like, you know, the DNA is coding for a protein that does something in the body. About 5% of that could be traced back to Denisovan DNA.

• 56:18Kelly Weinersmith?

  Wow.

• 56:18Daniel Whiteson?

  I'm intrigued by your use of the word us and Denisovans. Like, aren't we the Denisovans? Aren't we all just descendants of all? These people.

• 56:25Speaker 05

  Yeah, exactly. And that's I think we're starting to come around to thinking about it exactly that way. At least I am, right? So when we say that we, you know, we made it with them, we had kids with them like that gives you a sense of like, how did people at the time think about them, right? Like, well, I'm fascinated by by imagining what that world was like, what that interaction was like. And obviously, we don't know any of the details about how the interaction took place. You know, was it consensual or not? Who knows? But we do know that a child was conceived and that child was was cared for. And that does, I think, tell us something.

• 57:00Daniel Whiteson?

  I mean, I've read Clan of the Cave Bear.

• 57:01Speaker 05

  Yeah, that's right. I mean, that's exactly, exactly.

• 57:04Kelly Weinersmith?

  So there have been a lot of hominids. We argue about how many species there have been, but now there's only us. And so what happened to the rest of them? Did they breed with us and they're still with us today? Did they die off? What, uh, what happened?

• 57:18Speaker 05

  Yeah. So, I mean, you can think in some sense that like Denisovins and Neanderthals, because we have some, you know, Neanderthal DNA in in us today as well. In a sense, they're still here. And as Daniel said, they are us, right? I mean, if we have their DNA, then then why do we say that they're extinct? I think the thing is that like now we have enough fossil evidence. And we found more fossil evidence, by the way, for Denisovins. So what I was talking about is the initial discovery. We have now found more fossils, including a very intact skull that has a fascinating backstory. And so we're starting to know more about what physical features they had. We do know a ton about the physical features of Neanderthals, which lived more in in Europe and Central Asia and Western Asia.

• 58:02Speaker 05

  And so they had physical features that are different enough from people living today that, you know, for the most part, what people say is, you know, wouldn't pass the subway test, right? Which is to say that like, you know, if if a Neanderthal or Denisovan were were, you know, about to board a a subway in New York or any city, for that matter, uh, you know, would would would someone look twice?

• 58:24Daniel Whiteson?

  That says a lot because New York City has some weird people on the subway.

• 58:28Speaker 05

  Well, exactly. I guess, you know, that's that's why the subway test sort of rings true. It's like, people are willing to accept a whole wide diversity of humanity as just being totally normal.

• 58:38Daniel Whiteson?

  Yeah.

• 58:38Speaker 05

  But the Neanderthals, if if a Neanderthal boarded the subway, you might look twice, you know? So so in that sense, it's like, well. Humans that look like that aren't around today, but they did leave a legacy. I mean, they left a legacy in our DNA. And there's interesting examples of like particular genes, traits, things that, that, you know, happen in our bodies that we can actually trace back to Neanderthals and Denisovans in some cases.

• 59:05Kelly Weinersmith?

  Amazing. But what happens to the, okay, so forget Denisovans and Neanderthals, the rest of them, where did they go?

• 59:12Speaker 05

  Yeah. So, so in the case of other hominid species, partly, we don't know whether any of their DNA has survived in, in modern humans because they lived long enough ago that we haven't been able to get any intact DNA from those fossils in order to be able to like, understand their, their genetics. So it's possible that some of those older ones, like, you know, Homo erectus, for example, you know, there might be Homo erectus genes in us today, and we, we just don't know because we haven't been able to look at a Homo erectus genome. But in other cases, there's certainly lineages of hominids that we don't think left any descendants that are still alive today. So yeah, there's a big question of like, why us and not them, right?

• 59:54Speaker 05

  And there've been debates about, did our ancestors kill them? Did we just outcompete them? We were smarter, we were faster, we were better at working together, you know? And so, you know, the short answer is, we don't know. That's a, that's an ongoing debate. But I think the, the fascinating part that we now do have a better insight into from looking at Neanderthals and Denisovans is that part of the answer is, we, we mixed with them. We, we interbred with them. And as you said, we, we are them in a sense, and they are us, and there's, and they're still with us in some way. And maybe that was what happened further back as well. And we won't know until we're able to, hopefully someday, get some DNA or, or protein, some

• 1:00:37Speaker 05

  other kind of, you know, molecular evidence that would allow us to, to answer some of those questions.

• 1:00:42Daniel Whiteson?

  And so as we look back in time, how far back would you consider our ancestors to be modern humans, the kinds of people who would get on the subway or could just like be plopped into modern society, grow up in our schools and become a totally normal person?

• 1:00:57Speaker 05

  Yeah, so it's it's hard to say where we draw that line, but I mean, one way to do it is to say our species Homo sapiens as we currently define it, right? So, you know, paleoanthropologists who study human evolution, they give a name, a species name, to every fossil that they find or every, you know, piece of fossil that they can get a genome from. And so only those that are given the name Homo sapiens are technically our species as we currently consider it. So the way you could answer that is how old is our species Homo sapiens? And the answer is, yet again, that people debate this, but it's between 200,000 and 300,000 years old. So that's kind of the brackets on when are the earliest

• 1:01:41Speaker 05

  fossils that some people attribute to Homo sapiens? So somewhere in the 200 to 300,000 year old range, which again, I always say, like, to me, that's so recent, like, our species is so new to this planet. That's yesterday in the, you know, perspective of evolutionary biology.

• 1:02:01Daniel Whiteson?

  But just to underscore that, you're saying if you took a baby from a quarter million years ago and time traveled them into the future and were raised by a normal human family, they would be indistinguishable?

• 1:02:13Speaker 05

  Well, there are some ways in which anthropologists distinguish between what they call archaic Homo sapiens and what they call anatomically modern Homo sapiens. These are getting into like what I would consider to be pretty like nuanced anatomical differences in, in, you know, skull shape and which features are slightly larger and these types of things. So this is the sort of splitting hairs part of doing this kind of science that, you know, can be challenging when you start to get into like reading the research papers. But, you know, it's still Homo sapiens. So as far as I'm concerned, like, I think, you know, there's interesting, certainly. Questions to ask about like, well, what changes were taking place?

• 1:02:55Speaker 05

  Certainly, there are, you know, must have been some differences, even if it's cultural differences between the people living then and the people living today. But anatomically, physically, right? Like, if you look at the skull of an early Homo sapiens and the skull of somebody from today, they're very similar. I mean, they're very, very much like us.

• 1:03:17Daniel Whiteson?

  You'd have a beer with them?

• 1:03:18Speaker 05

  I would, yeah.

• 1:03:20Kelly Weinersmith?

  I also feel like Daniel's question is like laden with his assumption about what makes people human. Could they survive today in our modern era? And I think plenty of people would argue that's, that's not the important thing about humans. It's, you know, maybe social behavior or language or chins. One of our listeners said chins and I don't understand the chin thing.

• 1:03:39Speaker 05

  The chin thing is super interesting because it's one of the few physical features you can see in the fossils that distinguish Homo sapiens from other species. We are the only hominid that has a chin. So what did the chin do for us? I don't think anybody really has, has given a satisfying answer to that one. It's, seems to be an example of a trait that comes about through evolution, maybe just randomly and, and persists. It doesn't, not all the traits have to have a, an adaptive value. It doesn't always have to be useful for something. They can just come about, but I do like my chin, so I'm glad we have them.

• 1:04:13Kelly Weinersmith?

  I like mine, too. All right. That was fantastic, Scott. Thank you so much for telling us all about ancient humans. But you're not just interested in ancient humans, you're interested in like ancient human evolution and future human evolution. So tell us about your upcoming book.

• 1:04:26Speaker 05

  Yeah, well, I, you know, I've been interested in like the idea that humans are still evolving for quite some time, right? So, so my first book, published in 2016, was called Future Humans: Inside the Science of Our Continuing Evolution. And that's all about the ways in which, you know, natural selection and other evolutionary processes have continued until today. But then, more recently, I've been exploring this one particular possibility for our evolutionary future. And that is, what would happen if some of us left Earth and created settlements on other planets? Something that- You have also thought quite a bit about Kelly. I know we've had lots of conversations about the idea of space settlement and it's been super fun.

• 1:05:10Kelly Weinersmith?

  I love our parallel careers. You're ants and space and I'm parasites and space. And we're both in like an evolution and ecology sort of track and a space future of humans in space track. And anyway, it's always fun talking to you.

• 1:05:22Speaker 05

  I guess that tells us that there's a lot of ways to get to space, huh?

• 1:05:25Kelly Weinersmith?

  That's right.

• 1:05:27Speaker 05

  And so, yeah, I mean, so basically, yeah, I've spent the last several years doing a deep dive into this question of, you know, if at some point people are successful in creating space settlements, what would that mean for the people living in those space settlements? Like, what would happen to the descendants of those first pioneers, those first settlers on, you know, Mars or anywhere else for that matter? You know, questions like, could a baby born on Mars come back to Earth? And, you know, would people gradually adapt to the conditions on that planet? And would they eventually become a new species of human?

• 1:06:08Speaker 05

  So, yeah, so the book is called Becoming Martian: How Living in Space Will Change Our Bodies and Minds. And it comes out February 17th of 2026. So I'm super excited and it's actually already available for preorder if folks want to get a copy.

• 1:06:24Kelly Weinersmith?

  And I got to read it and I can say that it's amazing. And it starts with a foreword by astronaut Scott Kelly, which is, the Wiener Smiths didn't snag an astronaut foreword. So bravo. Not that the Wiener Smiths are, you know, a bar against which anyone should judge themselves, but I was pretty excited you got an astronaut foreword.

• 1:06:41Speaker 05

  Well, thank you. No, I was too. That was a real wonderful thing that Scott Kelly agreed to contribute a foreword. But you and Zach actually helped tremendously with this book, both in terms of sharing ideas and notes and reading, you know, draft copies and support all along the way. So, super appreciate it.

• 1:06:59Kelly Weinersmith?

  Our pleasure. Yay, space and yay, Scott. Okay, so everyone should pick up Becoming Martian and we'll see you on the next episode. Thanks, everyone.

• 1:07:08Speaker 05

  Thanks for having me on again.

• 1:07:15Kelly Weinersmith?

  Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We would love to hear from you.

• 1:07:21Daniel Whiteson?

  We really would. We want to know what questions you have about this extraordinary universe.

• 1:07:27Kelly Weinersmith?

  We want to know your thoughts on recent shows, suggestions for future shows. If you contact us, we will get back to you.

• 1:07:33Daniel Whiteson?

  We really mean it. We answer every message. Email us at [email protected].

• 1:07:40Kelly Weinersmith?

  Or you can find us on social media. We have accounts on X, Instagram, Blue Sky, and on all of those platforms you can find us at D and K Universe.

• 1:07:49Daniel Whiteson?

  Don't be shy. Write to us.

• 1:07:53Daniel Whiteson?

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