The Science Of How Smells Work - Harold McGee | Modern Wisdom Podcast 257

Harold McGee is an author and food expert. Our sense of smell sits at the front of our daily experience and yet our understanding of what smells are and how they're processed is almost non existent. Expect to learn why smell may be the oldest of our senses, how our brains combine what hits our nose to create sensations, whether smell will be the new frontier for the entertainment industry, what an opera singer smells like and much more... Sponsors: Get 25% discount on all mindful toiletries from Michael Hannah at https://www.michaelhannah.co.uk (use code MW25) Get 20% discount & free shipping on your Lawnmower 3.0 at https://www.manscaped.com/ (use code MODERNWISDOM) Extra Stuff: Buy Nose Dive - https://amzn.to/3qHCEAY Follow Harold on Twitter - https://twitter.com/Harold_McGee Get my free Ultimate Life Hacks List to 10x your daily productivity → https://chriswillx.com/lifehacks/ To support me on Patreon (thank you): https://www.patreon.com/modernwisdom #smell #biology #haroldmcgee - Listen to all episodes online. Search "Modern Wisdom" on any Podcast App or click here: iTunes: https://apple.co/2MNqIgw Spotify: https://spoti.fi/2LSimPn Stitcher: https://www.stitcher.com/podcast/modern-wisdom - Get in touch in the comments below or head to... Instagram: https://www.instagram.com/chriswillx Twitter: https://www.twitter.com/chriswillx Email: [email protected]

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

• 0:00Speaker 00

  It's really intimate, that receptor in the nose that's detecting what's out there. In order to make its report to the brain, actually binds to the molecule, grabs onto it. So for a moment, a split second, that's right, that that thing that you're smelling is part of you.

• 0:19Chris Williamson?

  What have you spent the last few years researching?

• 0:25Speaker 00

  Smell, and more particularly smells. So things in the world that we encounter and experience every day,

• 0:37Speaker 00

  that we generally don't pay a lot of attention to, and that turn out to be really, really, well, at least interesting enough to me to spend 10 years on it.

• 0:46Chris Williamson?

  Wow, I mean, interesting enough to write, everyone who's watching on YouTube is going to be able to see the size of this tome here. I also have to admit, I ruptured my Achilles a couple of months ago, and this is the only book that was high enough to work as a step for when I also needed to do some of my exercises. So also, it's got, it's got multiple uses. Let's, let's start then, let's define our terms. What is a smell?

• 1:12Speaker 00

  So a smell is a perception that we human beings have that's actually generated in our brains, but it is stimulated by molecules in the world, little bits of the things around us. So in that sense, smell is the most direct contact we have with the world, because sight is a matter of, you know, reflected light waves, and hearing is pressure waves in the air. It's smell that actually gives us information about the particular things themselves, and we detect them by noticing molecules of theirs that are small enough

• 1:57Speaker 00

  to escape those things and fly through the air so that we can inhale them. And when we inhale them, they interact with a receptor in the nose. The receptor then reports that it's received something from the outside world to the brain, and then the brain deals with that. It, it turns that information.

• 2:19Speaker 00

  Into a perception, but not just based on that one thing alone. It's based on all the other information it's getting at the same time and our database of experience. And then it gives us a, an interpretation of what it is that we've encountered.

• 2:36Chris Williamson?

  Where does a smell manifest? Because a touch manifests where, where on my body is affecting the object, a taste manifests on my tongue. How, how does a smell make the sensation of a smell?

• 2:48Speaker 00

  That's a great question. And it turns out that because the brain is trying to integrate all this different information, it's kind of leading us to, how should we say, ascribe the smell to the thing, something around us. You know, we're detecting it in our nose, right here. But we don't generally think of smells as-

• 3:16Chris Williamson?

  I don't feel it in my nose, yeah.

• 3:17Speaker 00

  Yeah, yeah. And it's really interesting what happens when we eat something because smell is a very important aspect of flavor, really the dominant aspect of the flavors of foods. And what's happening when we detect the smell from food is that, or we can call it aroma, nicer, nicer term for foods. When we have something in our mouth, when we exhale, air passes from the mouth through the nose, out, and it's that route that gives us the impression of what's in our mouth. And it turns out that, you know, when we think about the flavor of food, we think of

• 4:01Speaker 00

  the flavor being in our mouth. Because that's where the food is. But in fact, the smell is being detected up here. So the brain kind of relocates it to the place where the, the action is. And that's why we think that the, the smell is there rather than there.

• 4:20Chris Williamson?

  Can you impact the taste of something by affecting your breathing technique then?

• 4:27Speaker 00

  Yes, absolutely. And it, I mean, lots of different things to say about that. But, you know, one of them is simply how, how much of those molecules are introduced into your nose. And that has to do with how close you are to the thing, how deeply you breathe in, how often you breathe in. You know, sniffing is a way of, you know, picking something up. You're, you're, you know, there's something out there, but you're not quite sure what it is. So you're sniffing it out. That sniffing is repeated intakes of those molecules to give our receptors and brain another chance to figure out what it is.

• 5:12Chris Williamson?

  I always noticed when, everyone will know this, you put your hand down toward a dog and it, it smells your hand, but it does it in a sort of a, it does that very quick in and out. I'm going to guess that that's what the dogs are trying to do. What's the difference when smelling something between one long inhale and multiple very short inhales?

• 5:35Speaker 00

  Well, with, with one long one, what's going to happen likely is that your receptors will not have time to reset. You know, if you keep breathing in the same thing constantly, your brain will actually pay less attention to it because it kind of becomes kind of part of the, the background, you know, the wallpaper of your experience. Whereas if you breathe in and out, the, the sensation is going on and off. And your brain is able better to pay attention to that and perhaps identify what it is that's, that's doing it. And by the way, animals' sniffs are really, really short. You know, they're fractions

• 6:19Speaker 00

  of a second. I've, I've, you know, tried to time myself. I, I can't do that.

• 6:24Chris Williamson?

  I would look, I would pay good money to watch that video of you trying to time your, your sniffs.

• 6:34Speaker 00

  But it's it's fun, you know, it's it's a sense that we kind of take for granted that we don't really exercise. And, you know, it's it's really easy to do. You can do it just sitting right here, talking to each other. I mean, one of the things that I write about in the book is the smell of a laptop. You know, if you stick your nose down next to the keys and inhale, you'll get the smell of the the circuit boards in there, which are made of particular molecules that are given off. And so it has a very particular smell. So it's it's something that that's one of the reasons I loved the last 10 years, even though it was

• 7:18Speaker 00

  kind of a long haul, is that there's just so much out there to pay attention to that we generally don't.

• 7:24Chris Williamson?

  One of the things that I really enjoyed that you said at the beginning was about how it's one of our most direct senses. And you're correct, like, touch, a smell is kind of like touch, if the thing you are touching turned into a volatile and went inside of you.

• 7:41Speaker 00

  Yes, that's right.

• 7:42Chris Williamson?

  Little bits of the thing that you're touching, getting in you, and then you noticing it in a completely different way.

• 7:51Speaker 00

  Yeah. And in fact, it's it's really intimate. So that receptor in the nose that's detecting what's out there, in order to make its report to the brain, actually binds to the molecule, grabs onto it. So for a moment, a split second, that's right, that that thing that you're smelling is part of you. And

• 8:13Chris Williamson?

  That's very dangerous. When I think of some of the smells that have entered my nose, I don't know if I want to be a part of them.

• 8:19Speaker 00

  Exactly, exactly. It it's, you know, it explains perfectly why it is when something doesn't smell so good, we hold our nose. We don't, we don't allow ourselves to take it in, because we have this kind of sense that it's becoming too, too close to our insides.

• 8:38Chris Williamson?

  Why can we detect smells?

• 8:43Speaker 00

  We can detect smells mainly because our animal ancestors are able to do that and have been able to do that from the earliest forms of life on Earth. And that's because it's really important for living things to know what's around them in order to know, you know, what direction food might be, what direction something dangerous might be. And so, chemical sensors, and that's what the sense of smell is, a chemical sense, is probably the earliest sense that living things had.

• 9:21Chris Williamson?

  No way, even before eyesight?

• 9:25Speaker 00

  Oh, eyes are really complicated structures, you know, bacteria have chemical senses. Things that we think of as being really primitive and not really doing anything except, you know, going blindly through the world, hoping to luck out, finding some food. No, they have senses, systems for detecting molecules and then changing their behavior in order to take advantage of that information.

• 9:55Chris Williamson?

  And that would be more analogous to smell than it would be to any other sense?

• 10:01Speaker 00

  That's right, that's right, because it is, again, latching on to a molecule. Taste is also a chemical sense. And so you could say that these early forms would be a combination of taste and smell.

• 10:16Chris Williamson?

  I was looking at, I can't remember what I was learning about E. coli bacteria living in the gut. And basically, they can spin one way and it makes them go in a circle, or they can spin the other way and it makes them go straight. And they basically have an if this, then that function, which is if the, I think that they might be looking for perhaps glucose. If the area that they move to has more glucose, then spin in the direction that makes them go straight. If it doesn't, then spin in the direction that makes them the other way. It's like such a simple, you know, you could write it into a computer code in two minutes. But that's utilizing the chemical response.

• 10:56Speaker 00

  That's right. They have to have the receptor for glucose to know that it's out there. Exactly.

• 11:01Chris Williamson?

  Don't you? So smells are created by these little volatiles, tiny little particulates of whatever it is that goes on, and they're made up of something fundamental. I know there's five basic tastes, right? Is the same thing true with smell?

• 11:19Speaker 00

  No, that's the thing that makes smell really special. So it's true that we have these two chemical senses, taste on the tongue and smell in the nose. Taste is limited to about a dozen different sensations. There are arguments these days about exactly how many, but at least sweet, sour, salty, bitter, savory. Then some scientists would add a couple of others, but that's basically it. Smell, we have around 400 different receptors,

• 11:55Speaker 00

  which can act combinatorially to detect many, many different molecules. So thousands upon thousands upon thousands. And again, scientists argue about exactly how many, but it's way more than we can detect with taste. And it's what gives us the most particular information about the world around us.

• 12:28Chris Williamson?

  If smell is so fine, if the way that we can smell things, the combinations that we can come out with, so much greater than taste, I would guess that most people, if I said, you've got to lose one of your five senses, most people would lose smell and they'd be upset, but they probably wouldn't care that much. If you lost taste, you'd be a bit more annoyed. And then when you get into like the big three, that would be a real drop off. Why is it that smells got such a fine ability to adjust and this combinatorial particular formula if it's also something that we feel like we could dispense with quite easily?

• 13:09Speaker 00

  Well, it's, yeah, it's an interesting question. And in fact, a lot of people are facing that kind of issue these days with COVID. Because that's one of the early symptoms of a COVID infection is derangement, either loss or just complete mess up of smell and/or taste. And, you know, people respond differently. There are people who lose their sense of taste or smell for a variety of reasons.

• 13:45Speaker 00

  I myself lost my sense of smell while I was writing this book, which was a little disturbing.

• 13:55Chris Williamson?

  Suboptimal, yeah.

• 13:56Speaker 00

  Yes, yeah. So, and it really does depend on how important it has been to you in your life up to that point. And in fact, my experience was that there was just no pleasure left in eating. You know, you would satisfy the growling stomach, but then that was it. You know, there was really no point in spending time cooking, no point in going to a restaurant and paying good money, because I was just kind of filling this hunger that gave me no satisfaction.

• 14:31Chris Williamson?

  I guess all that you've got left...

• 14:33Speaker 00

  No sense of satisfaction.

• 14:34Chris Williamson?

  All you've got left is texture, right? Is that it?

• 14:37Speaker 00

  Well, taste also, because I didn't lose my sense of taste. So I could still get sweetness and bitterness, but pungency, you know, hot pepper is actually a touch sensation. And that is something that you can still feel. And a lot of people will try to compensate for the absence of these other sensations by upping that. Uh, stimulation.

• 15:09Chris Williamson?

  Yeah.

• 15:10Speaker 00

  But uh, yeah, I would, I personally would just hate to lose either of them, taste, taste or smell either one. Uh, you might think the taste might be easier to get rid of because it's only, you know, those four or five different sensations. Um, but people who lose their sense of taste, uh, report the same kind of thing. They can still smell foods, but when they eat them, it's, the, the brain can no longer make that connection that those smells are in here. So it's, it's more like, you know, eating perfume or something like that. It's not satisfying in the, in the same way. It's not, not grounded.

• 15:48Chris Williamson?

  Yeah, I bet it's not. Are there any technologies that are interacting with smells now? Are we gonna get an entertainment system that kicks some smells out when we're watching a TV program or anything?

• 15:59Speaker 00

  Well, actually, uh, that, that idea's been around for a while. Uh, Smell-a-vision was a, an experiment back in the-

• 16:06Chris Williamson?

  That was always going to be the name, wasn't it? Anyone that didn't use that name was ju- they were losing out.

• 16:12Speaker 00

  That's right. And in fact, uh, you know, there's this, uh, American film director, John Waters, who does, um, interesting kind of offbeat movies. And he did one back in the 1970s that, uh, involved a, a scratch and sniff card. So you walked into the theater, uh, and with your ticket, you were given one of these cards and then you were cued by the movie as to when to scratch and sniff. And there were very nice smells and really disgusting smells on that card. Um, and I, I actually, uh, dug that card up, uh, like

• 16:51Speaker 00

  a year ago, so maybe 30 years after I took it home with me from the movie showing and I scratched and sniffed and those smells were still there. So that's the robust technology. Um, the, the newer idea is to use some kind of digital coding so that you have a, a little box next to your computer and, um, it releases some combination of volatile molecules in response to what it, whatever it is you're trying to, um, uh, synthesize. Uh, my experience so far has been that it's, it's not really very effective.

• 17:31Chris Williamson?

  The technology's got a way to go. I went on a, I want to call it like wings of flight or something. It was Disneyland in LA last year and you go on this big ride and you sort of up in the air and it's one of those ones where the screen is moving and you're pivoting and twisting around with it. But this had, you would be going over the African plains and they were pumping the smell of grass in and you were flying over the top of the ocean and they were pumping the smell of sea spray in. And that was, that was pretty cool. It was the sort of thing that stuck in my memory because I think it's so rare that we get, at least from an entertainment perspective, it's so rare that we have our smell manipulated, right?

• 18:12Speaker 00

  That's right. People have done operas, smell.

• 18:17Chris Williamson?

  Smelly operas.

• 18:19Speaker 00

  Yeah, yeah, exactly.

• 18:21Chris Williamson?

  What does an opera man smell like?

• 18:25Speaker 00

  But the problem with, with things like operas and plays and concerts, things like that in general is that you're sitting in a seat which is stationary and they have to blow the, the smells at you in, in this, you know, cavernous room and then get them out of there in time for the next one. And the smells don't do that really easily. You know, the molecules kind of hang around. And so you really have to design an amusement park thing like that with those things in mind.

• 18:59Chris Williamson?

  What are some of the tricks that we can play on our physiology with smells? Can we use them to affect us positively? You know, I've seen sleep sprays that you spray on your pillow before you go to bed and there's awakeness this and, you know, caffeine in a, in a smelly bottle that. Is there any efficacy to these? And are there any other things that we can do to sort of utilize smells to, to help us?

• 19:25Speaker 00

  Well, there are studies that have shown that particular smells in particular cultures can have physiological effects, generally speaking, either relaxing or stimulating. You know, it doesn't really get any more fine-grained than that. And it is culture-dependent, so it's kind of what you associate those smells with, apparently. I mean, it's not an easy thing to study in a systematic way, but generally speaking,

• 19:58Speaker 00

  it seems that lavender is a relaxing smell for most people, and citrus smells are stimulating, which is kind of interesting because they actually share some components. You know, smells are, we think of the smell of lavender or the smell of a lemon as being some unitary thing, like molecules of lemon, molecules of lavender. But in fact, what these volatiles are, are, they're bouquets.

• 20:36Speaker 00

  They come at us in large numbers, and what our brain does is register the overall bouquet and then interpret that. And so it's more like a chord in music, rather than particular notes, we're sensing the whole thing. And it turns out that lavender and citrus share notes. So why they should have divergent effects on people is an interesting question.

• 21:06Chris Williamson?

  It's fascinating, it's fascinating that so much of what a smell means to us is based on our history with it, our interpretation of it. Even when we think about what smells nice and what smells bad, like if you think sort of rotting meat at one end and fresh grass at the other, there's a reason for that, right? That it's become embedded in us. Our evolutionary ancestors would have found it advantageous to know that that meat is off and this grass is fresh, and therefore the effect that it has on us. And then obviously, you can have that sort of more epigenetically within your lifetime. Where you're thinking, okay, I remember mum used to put lavender on my pillow when I was

• 21:49Chris Williamson?

  sick as a kid, therefore I really like lavender. I love old bas oil, because that was the thing that I had on the radiator when I was ill. So I've got it on the radiator now, I'm still 32 years old, a massive child. But yeah, it's fascinating that the smell itself kind of is just a thing. And we then run forward with that a lot further. We interpret it, it becomes this subjective, very narrative, personified interpretation of what that means.

• 22:16Speaker 00

  Exactly. And it's kind of interesting, you know, it does seem to make sense evolutionarily that we know the difference between rotting meat and fresh fruit, for example. On the other hand, it also turns out that in human development, there are several years in kind of toddler, the toddler era, where we human beings are totally neutral when it comes to to smells, or much more neutral than adults are. And, you know, you can see this with little children who are sticking their hands into things that aren't such a good thing to stick

• 22:57Speaker 00

  our hands in, because they don't have the same revulsion, automatic revulsion that adults do. And it's unclear, you know, why this is exactly. I mean, it's important for developing animals to, you know, have a broad enough tolerance for things that they can actually feed themselves and thrive. On the other hand, it's also important to be able to distinguish among poisonous things and not so poisonous things. So why it is that there's this window of flexibility,

• 23:36Speaker 00

  why it is there's this window of flexibility is still unclear.

• 23:40Chris Williamson?

  Yeah, that is interesting. What are some of the most unique smells that you experienced?

• 23:47Speaker 00

  That's a tough one. I really didn't know much in perfum world before I started writing about smells. You know, food and drink has been my thing for decades. This was kind of out of that. But that just ended up becoming really fascinating to me. And there are particular incense woods that are also used in perfumery that are just intoxicating. You know, if you... I went to Japan a few years ago and was indoctrinated in this practice they have called... The English translation is incense listening.

• 24:32Speaker 00

  So rather than just lighting a stick in your room and just kind of floating on that, you actually sit down and focus on a particular little bit of incense wood, and it smells, and think about it. And then take another little bit of a different wood and think about it. Really pay attention to what the qualities are. So it's like, you know, learning to taste wine or something like that. And a couple of those woods were just, you know, they had to pull me away from the table. They were just so, so beautiful. And kind of hard to describe because they're, you know,

• 25:16Speaker 00

  like trying to describe a lemon, you know, a lemon is lemony. And these incense woods just had this character that was something I had never experienced before and that was just really rich and just kept you wanting to smell more because there seemed to be layer on layer on layer.

• 25:34Chris Williamson?

  Can you remember the name of them if people want to try and buy them online?

• 25:37Speaker 00

  Oh yeah, uh, it's the one I particularly love has several different names. So it's one is agar wood, A G A R wood. Uh, it's sometimes also known as oud, which is O U D. Uh, and uh, another couple of names that are escaping me at the moment, but, but either of those will, will get you there.

• 26:03Chris Williamson?

  Got you.

• 26:03Speaker 00

  And it's, it's really interesting stuff. It's, um, it's produced by, uh, a Southeast Asian tree that has become infected by a fungus. And in response to that infection, it generates this resin to defend itself. Uh, and it's that resin that gives it that, that amazing aroma.

• 26:27Chris Williamson?

  It's so crazy how the downstream effects of things, uh, and end up to this combination. But as you say, if we've got 400 different dials on the mixing desk that we can play around with, and each combination of those comes out differently, it's not surprising that you might get odd results from something that you, uh, you wouldn't have thought of. What animal smells did you look at?

• 26:47Speaker 00

  Uh, um, uh, as many as I could think of and find. Uh, so actually in the, in the incense and perfume world, that again was something that came as a surprise to me. Uh, we might think that animal smells are generally not that pleasant compared to woods and flowers and fruits and things like that. Uh, but it turns out that animal materials are really important in perfumery. And they're, uh, among the most valuable ingredients there are for perfumery. One of them, uh, the, the one that I think has the most interesting backstory is ambergris

• 27:29Speaker 00

  or, uh, ambergris. Uh, so this is, uh, a material that comes from the, uh, lower digestive tract of the sperm whale.

• 27:45Chris Williamson?

  I want to know who the first guy is that was that thought that sperm whale that we just caught over there. Anyone has anyone sniffed its lower digestive tract recently because I'm certain I'm absolutely certain. Boys, if we bottle that, we've got a million pound business there.

• 28:01Speaker 00

  Well, we do have over here this this classic novel, Moby Dick about the whaling industry. There's a lot about ambergris in in Moby Dick.

• 28:13Speaker 00

  But it wouldn't have been quite the scenario you propose. Because what would happen is that the the whales swimming in the ocean would die. Their carcasses would would come apart and these bits would end up being washed up on the beach. Or on the shore all over all around the world. And in fact, this is still the way that most ambergris is is found is just by chance. People walking on the beach and coming across a lump, which looks like nothing in particular. Which again is it's kind of hard to describe, but it's not fishy the way you would expect.

• 28:53Speaker 00

  It's flowery and yeah, just kind of transcendent smelling. But it came from the lower digestive system of a sperm whale.

• 29:05Chris Williamson?

  What other animal stuff did you look at?

• 29:09Speaker 00

  Well, let's see, I asked the question, why does excrement smell the way it does? And what information might that give us about what's going on? And that turns out to be, at least if you're willing to think about things like that. Pretty interesting because, you know, we've discovered in the last 10 years that we have this microbiome in our guts that are whose number of cells outnumber human cells in our own body. And the this collection of microbes has a tremendous effect on our health,

• 29:50Speaker 00

  on our digestion, on just all all aspects of our lives, pretty much. And it turns out that because excrement is coming from their home, it carries the the signatures of the microbes that are in there and what it is they're up to.

• 30:11Speaker 00

  And so there are particular, how shall we say, particular excremental bouquets that indicate that things are working pretty well and others that indicate that that there are bacteria in there making things that are not as good for us as as the other microbes. So the closer that that smell comes to the smell of newborn babies poop, the better. And the more the the more sulfurous and just offensive it is, the

• 30:52Speaker 00

  more it indicates that, in fact, we're feeding the the bacteria that tend not to be good for us. And so we might want to switch to a diet that gives us something more like what the what the baby gives us.

• 31:09Chris Williamson?

  Switching back to that, our smells or what how we interpret smells are narrative personifications, they're also evolutionary indicators of what's going on. Presumably that's adaptive, that we wouldn't have been disgusted or concerned or felt made to feel sick by excrement, potentially ours, which didn't have this stuff in, because there's no real difference. It's not like one smell is worse objectively and one smell is better objectively. It's how we interpret those, right? And the signal that that gives off.

• 31:49Speaker 00

  Exactly. Yeah. And in fact, there are examples that I give in the book of creatures that in fact consume excrement. And some of them consume their own. So the gorilla, which is a close relative of ours, has been observed many, many times catching the excrement as it comes out and bringing it up and smelling it and enjoying it and then having some. So.

• 32:25Chris Williamson?

  I wonder how many people opened this podcast today and thought that they would hear the word excremental bouquet and then imagine imagine a huge gorilla sniffing its own poop.

• 32:38Speaker 00

  Yeah, yeah.

• 32:39Chris Williamson?

  Well, this is this is the world that you have been in for the last decade, Harold. So who are we to complain about it? What about plants? What did you learn about the smells that plants give off?

• 32:48Speaker 00

  Well, so if you think about the the general contrast between animal smells and plant smells, animal smells, we generally find not so pleasant. Plant smells, we generally find very pleasant. Flowers, for example, and fruits. And you mentioned the smell of freshly cut grass, all very, very pleasant. And it turns out that one of the main differences between plants and animals is that the smells of animals are essentially the smells of the breakdown of our tissues, either naturally, because metabolism involves breakdown as

• 33:31Speaker 00

  well as building things up, and because the microbes are living off of us. And so their waste products are also ours. In the case of plants, most of the smells are actually created. They're not breakdown products. They're created by the plants, synthesized by the plants for very specific purposes. And they're larger molecules. They're not the the small ones that make animal smells less pleasant. They're large, complicated molecules. And there does seem to be evidence that the larger and more complicated a molecule

• 34:13Speaker 00

  is, the more likely we are to find it pleasant. And that kind of makes sense, because it indicates not decay, not breakdown, but in fact, something being created, something being synthesized, and so a potential source of food for us.

• 34:32Speaker 00

  So plants make thousands upon thousands of different molecules that we find pleasant. The interesting thing, kind of evolutionarily, is that those smells are there not to attract animals for the most part, but to repel them, not to attract other living creatures, but to ward them off. They're a form of chemical warfare. And that's because unlike animals, plants are stuck in one place. They can't run away. So they have to do something to discourage animals that can move around from chomping on them. And many of the things

• 35:13Speaker 00

  that we enjoy in herbs and spices and even flowers are there to repel animals and prevent them from consuming the plant.

• 35:25Chris Williamson?

  It feels like we have quite an emotional attachment to a lot of different smells, but we don't have that necessarily with some of our other senses, specifically not with sight, or probably quite as much with sound. I wonder how different people would live their lives if... I've been a big champion of people trying to spend as much time in nature as possible, reconnect with the grandeur of the cosmos by looking up at the night sky and making yourself feel insignificant and things like that. But the detachment from the narrative, if we were able to smell the smell of the night sky, the effect that that has through our eyes, I feel like that would be much more pungent. I feel like it would be a very, very strong sensation. Do you get what I mean? That it's much more...

• 36:08Chris Williamson?

  what is good for us in terms of what we view and what is good for us in terms of what we smell are actually much more messy on sight, despite the fact that of 14 million sense cells we have in our body, 11 million of them are discriminated towards vision.

• 36:26Speaker 00

  Mm-hmm.

• 36:27Chris Williamson?

  I just think it's really interesting. It would be an interesting world in which we attach that same narrative perhaps, and the same level of emotion and buy-in to sight and the things that we saw.

• 36:42Speaker 00

  Yeah, so a couple of things are going on. One is that the way the brain is wired, the sense of smell goes much more directly to the emotional centers of the brain than the other senses do. And that may have to do with the fact that the chemical senses are as primitive as they are, and therefore we're kind of there in the brain long before we had good vision

• 37:12Chris Williamson?

  or hearing.

• 37:13Speaker 00

  Yeah, yeah. And so they go much more directly to the parts of the brain that would make that kind of impression upon us. The other thing is that, and I haven't seen scientists talk about this, but I think it's important. With vision, it's kind of on all the time, right? We're taking in visual information constantly unless we sleep or something like that. Whereas with the sense of smell, it's much easier, even though we're breathing regularly, it's much easier to ignore it, you know? I mean, we're sitting now, talking with each other. I don't have a particular sense for the smells around me at the moment because I've kind

• 37:57Speaker 00

  of adapted to this room. It's, brain has kind of tuned them out because it's a constant. Whereas my vision is working because I'm, you know, making eye contact with you and getting information from the screen. So I think smell is much more episodic, and therefore it's maybe easier to anchor a particular experience in it because it's not as continuous as vision is.

• 38:27Chris Williamson?

  I think that's a really, really good point. You, talking of nature and sort of the earth at large, you looked at the smell of land and waters sort of en masse as well. What did you learn there?

• 38:39Speaker 00

  Well, in the case of the land, it took me down a rabbit hole I never expected because you then, in order to ask why the land smells the way it does, you have to know what the land is. And the land is a really complicated thing that didn't exist, hasn't existed forever. It was created by plants over the course of, you know, eons and eons of time. And the smell of fresh dug soil, which is so evocative, so, again, refreshing and so on, is like the smells of plants in general,

• 39:22Speaker 00

  a molecule that's generated by living things in the soil. And at the moment, we actually don't know why that particular molecule is created. The dominant smell of the fresh soil is a molecule called Giosmin.

• 39:40Speaker 00

  And it's generated by a handful of bacteria that live in the soil. We don't quite understand why, because it's not toxic. It's not, you know, something to kill other bacteria or to ward off other creatures. It might be a signal to other bacteria that, you know, "I'm here and, you know, give me some space." Or, "I'm here and come on over so that we can exchange genetic material." It's not known. So, and then there's the smell of stones.

• 40:20Speaker 00

  You might have heard of something called petricor, which is a favorite term of people who are interested in perfumes, fragrances, but also just the smells of the world. That's supposedly the smell of rain on stone. So, you know, the smell of the sidewalk after a couple of hot days and then all of a sudden you get this burst of aroma. And it turns out that that smell is actually the liberation from that surface of all the stuff that's been flying around in the air for the last couple of days.

• 40:59Speaker 00

  So it's really not anything to do with the stone, which is what the the name suggests. It's more the smell of that place suddenly concentrated and and brought up for you to inhale. So I think it should be called Gaia Aikor, not Petricor.

• 41:20Chris Williamson?

  Uh huh.

• 41:20Speaker 00

  Gaia, because it's the it's the world, it's the planet that that we're smelling in that moment.

• 41:28Chris Williamson?

  Presumably, that means that Petricor or Gaia Aikor would be different on rocks in the middle of the Saharan plains as they would be in New York, as they would be in Japan, as they would be in wherever.

• 41:42Speaker 00

  Exactly, yeah, it's it depends completely on on what's around. And in the case of something like the Sahara, you know, uh, those volatiles may have been collecting for hundreds of years before they're liberated. And um, I I think there's something to be said for, you know, taking samples from a place like the Sahara and artificially wetting them and collecting the volatiles that come off and getting some idea perhaps of the uh, of what's going, what's been going on, what has been living in that area uh, over the last however long it had been since the the previous rain.

• 42:20Chris Williamson?

  I remember reading about bloodhounds and the fact that they can detect, is it like one part in a billion or one part in a trillion or something of particular volatiles? Have we got any equivalent with humans? Is there some humans with ridiculously overpowered senses of smell?

• 42:39Speaker 00

  Well, actually, we are able to detect some things at parts per billion also. In fact, Geosman is an example of that, and there are several others. We are, we can be very sensitive to particular molecules. And the people who work on the senses of taste and smell in human beings have been at great pains over the last few decades to point out that this idea that bloodhounds are better than us at smelling is not really true. Or at least it needs to be put into context, because bloodhounds spend their lives right

• 43:21Speaker 00

  next to the ground, and so they're very good at picking up things that are going on right next to the ground. If you give them a bottle of burgundy or of an English sparkling wine and ask them to, you know, distinguish one from another, they're not so good at that. But we are, you know, professional wine tasters can taste a sip of something and narrow it down to a very particular year and place and producer and method of production and all that kind of thing. So we have the same basic set of receptors, fewer of them, but the same basic set of receptors as other animals do.

• 44:02Speaker 00

  We have way more processing power to make sense of what it is that we're smelling. And so just to reduce smell to, you know, how sensitive your nose is to a particular thing just does an injustice to the amazing powers that humans have to make use of that information.

• 44:23Chris Williamson?

  Are there smell connoisseurs out there, like sommeliers of smell? Smell-iers?

• 44:33Speaker 00

  Not that I'm aware of, but I think it's a great idea. I think you may just have coined a term.

• 44:38Chris Williamson?

  Fine, fine. Anyone that wants to use that, you need to pay me money. Another thing that I was really fascinated by was the fact that you had like industrial smells in there as well. Burning and industry charcoal, stuff like that. And obviously that's something that we probably wouldn't have been very accustomed to. I don't imagine that a volcano goes off all that often and that we get the opportunity to smell it. So that must be a unique thing to study.

• 45:05Speaker 00

  Well, except that, you know, human beings, well, first of all, fire has been an important aspect of life on Earth for like half a million, half a billion years. You know, long, once there were enough plants on the planet to generate enough oxygen for a continuous burning to take place, there has been fire, which can be ignited by lightning and all kinds of natural things. And then when it comes to human beings, for probably on the order of a million years, we've been really dependent on fire for all kinds of things. So it's, it's something that we are

• 45:50Speaker 00

  even biologically very well acquainted with. And, and sensitivity to those smells would have been important even before we controlled fire. Because in order to, you know, escape a fire or to know that one is nearby without being able to see it, we had to be pretty sensitive to and aware of those particular molecules.

• 46:16Chris Williamson?

  Yeah. What do you think, I was considering this yesterday when I was reading the book. Do you ever think back to times in prehistoric history and think about what it would have smelled like? So I was reading about how in the time of the dinosaurs, there weren't actually any plants. It was all sort of ferns. It was this crumpled ground of ferns. And then if you were to go back further to single-celled prokryotic eukryotic life, it would be very sulfurous, right? It must be, it would be interesting to be able to take samples of that and actually work out what the earth smelled like. The place that we walk, but just in a time that we weren't.

• 46:54Speaker 00

  Yes, well, so in one of the early chapters of the book, I tried to do that. So I asked the question, what was the early Earth like? And when did it become more like what it is now? And it really did depend on the invention, first in microbes and then plants took it over, the invention of photosynthesis, which generates oxygen. Before there was an excess of oxygen in the atmosphere, everything would have smelled sulfurous. It would have been hydrogen sulfide and

• 47:36Speaker 00

  blanking out, yeah, the methane thiols and things that we immediately recognize as being something to be careful about. Now, hydrogen sulfide is important, an important component, the main component in the smell of hard-cooked eggs. So it's not always bad. But you know, if that same eggy smell were magnified by a hundredfold, then you wouldn't be happy. And that's the kind of smell that comes out of volcanoes and hot springs and so on. And that's what the world in general would have smelled like

• 48:15Speaker 00

  before we had enough oxygen in the air to oxidize those molecules and get rid of them.

• 48:23Chris Williamson?

  How has the study of smell, obviously, your background is majority of the in food up until now. How has your learnings from smell impacted your view of food? Or are you cooking in different ways? Have you changed up anything to do with the sort of tastes that you put into your foods to manipulate this?

• 48:42Speaker 00

  Not really. I just pay more attention. I guess that's the way to put it. And you know, when something doesn't smell quite right, instead of just pushing it away and saying, this is not very nice, I actually take more of it to try to figure out, you know, what's going on? What is it that doesn't smell so nice? And how might it have been created? You know, what went wrong in the cooking process? And it is true that I do probably cook with more different ingredients nowadays than I used to because I've become interested in just the diversity of aromas that the

• 49:25Speaker 00

  different natural materials have. And I do things like I now have tea bushes in my backyard and I make tea.

• 49:34Chris Williamson?

  Okay.

• 49:35Speaker 00

  Which by the way, I recommend to just about anyone because it turns out that the tea bush, even though we think of it as a, you know, an Asian exotic sort of thing, it's very hearty and it can take frosts, no problem. And to me, it's just the most amazing transformation. You pluck a few young leaves from a tea plant and smell them and they smell like green leaves. And you let them sit for a couple of hours or you just rub them a little bit and let them sit for 10 minutes to speed things up and then smell them. And they're like flowers. And it's, you know, all you've done is pick them or

• 50:18Speaker 00

  rub them. It's just an incredible thing that these, these leaves are engineered to be able to do. And again, it's a, it's a defensive reaction. There's a problem. So let's ramp up these molecules that help defend us. But we find them delicious.

• 50:35Chris Williamson?

  Ah, so that would probably to some common predator of that particular plant would actually be a little bit disgusting.

• 50:43Speaker 00

  It would be off putting to a predator and it's also, many of these molecules in tea in particular are also signals. So there's a signal from the leaf that has been damaged to the rest of the plant to say, ramp up your defenses, boys, because we've got a problem up here.

• 51:03Chris Williamson?

  Ah, that's really interesting. It's also a signal that it needs a little bit of milk and two sugars, isn't it? Moving, moving forward, looking to the future, are we going to see sense scientists coming up with anything new? Are there any sort of exciting areas in the world of sense science?

• 51:22Speaker 00

  Oh yeah, on all, on all levels. So we're getting better and better at detecting the volatile molecules that are out there in the world in tiny, tiny quantities and identifying them so that we know what it is that we're smelling and get some idea of their backstory, what it is that those molecules are doing there. So now you can, for example, put a little bubble around a flower in the jungle in South America and in an hour or so, extract enough of its aroma that you can then take it back to a lab and identify all those different molecules.

• 52:07Speaker 00

  It's, it's amazing. And then on the human side, we're learning more and more every year about the circuitry that's involved in our perception of smells and then our interpretation, how it is that our brain takes that information and turns it into a conscious perception on our part. So it's very exciting times.

• 52:31Chris Williamson?

  I like it. Harold's Nose Dive, a field guide to the word smells, will be in the show notes below. Any other things that people should go and check out? Any places you want to send them?

• 52:43Speaker 00

  Ah, well, I have a website and I write occasionally, updates and, and, you know, talk about other related things as well as food and the connection of all this to food and cooking. So that would be a place to start.

• 52:58Chris Williamson?

  And that, what is it? Is it balanced food? What's the website?

• 53:02Speaker 00

  HaroldMcGee.com.

• 53:04Chris Williamson?

  HaroldMcGee.com. That's it. Thank you very much for today, man. I really appreciate, really enjoyed it.

• 53:09Speaker 00

  Me too, Chris. Thanks so much.

• 53:26Speaker 02

  Mr. President, my company told me of the explosion on our rig. On October 2nd. Causing massive water displacement and triggering a tsunami. They all heap the blame on me. Tom Cruise is. Digger got us into this mess. And Digger's gonna dig us up. From the director of Birdman and The Revenant.

• 53:43Speaker 00

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• 53:47Speaker 02

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• 53:50Speaker 00

  I'm not the first daddy.

• 53:51Speaker 02

  Digger. See the trailer online. Only appears October 2nd. Rated R. Under 17. Not a middle without parent.