Episode AI notes
- Brain size expansion in humans started around 6 million years ago, with a tripling of brain size over the last 2 million years
- The expensive tissue hypothesis suggests that the brain is metabolically expensive, leading to potential trade-offs with other tissues like the gut
- Reducing gut mass may provide extra calories for brain development, impacting how the body processes calories efficiently
- Possible sources of extra calories for brain growth in early humans include meat-eating, tuber-eating, and offloading fermentation into the external environment
- External fermentation can break down indigestible starches, make nutrients more bioavailable, and support healthy internal fermentation
- Comparative studies on fermented, cooked, and raw diets can provide insights into caloric balance, metabolic indicators, and microbiome changes
- Evolution of preferences for fermented foods in primates could be linked to the external fermentation hypothesis and the early gene for alcohol dehydrogenase
- Existing apes and primates are attracted to fermented fruit, suggesting a role of fruit consumption in primate evolution and metabolic adaptations (Time 0:00:00)
The Evolution of the Brain Transcript: Speaker 1 Of the brain changed in evolution? And so I started from an interest in like what makes human brains unique and what makes other great apes brains unique. So I’ve always been really interested in chip bancies and other great apes because they’re so intelligent, they are able to engage in a lot of complex behaviors. They have language like communication abilities and things. And so I was kind of interested in what sets human brains apart and also what things make chimpanzee brain special or bonobo brain special, et cetera. Because I really started out very beginning. I started out as an evolutionary biologist before I studied neuroscience. So when I was in graduate school, neuroimaging kind of started exploding as a new methodology for comparing brains of different species. We’re getting at this point now we’re getting very high level, very high resolution scans. And we can do them on post-mortem brains so we can have brain scans of animals that we never would have expected. So like not just perhaps a lab monkey, but all kinds of species that people at zoos might have after an animal dies naturally. Many people are now building collaborations and we can access these brains and scan them and yet get these lovely beautiful images. And so what I generally do is look at connectivity differences. The short version is sort of one example is human language. We know there’s a large major tract with a lot of interesting long distance connections in human brains. It’s called the Arculo-Feciculus. And early on we’ve used these kind of comparisons we found, (Time 0:10:13)
The Evolution of Human Brain Size Transcript: Speaker 3 Are under positive selection, what changes in the brain in response. So yeah I guess you know Catherine and I are both interested in brain evolution generally with a focus on humans but I think we’re also both really interested in other animals as well. Speaker 2 So Catherine you already mentioned that one of the enduring questions in the field has been this question of why did human brain size grow so much right? Why did we become so encephalized as you put it? So maybe we could just give people a little bit more of a sketch of this. So how much did the human brain grow and over what time scale? What is the interesting story there? Speaker 1 So one thing you can use as a rough measure like how large a brain is something called the encephalization quotient. And basically this idea is you can look across all mammals and get a rough mathematical quotient for how large you would expect the brain to be based on the body size. And if you look at all different mammals patterns start to emerge and you start to see well as the body gets larger the brain gets larger but also in a consistent and a constant slope where You can predict pretty well for most species. But there are some species that are outliers which includes humans. One we could describe as the encephalization of quotient of humans is roughly around the last figure I looked at was like 6.8. So that would mean if an encephalization quotient of one would be what you would expect 6.8 is like six times the size that we might expect. (Time 0:12:18)
The Evolution of the Brain Transcript: Speaker 1 Last figure I looked at was like 6.8. So that would mean if an encephalization quotient of one would be what you would expect 6.8 is like six times the size that we might expect. And just because I think comparisons are useful if you look at chimpanzees they have a brain about a third of the size of humans but their body size is fairly close to ours. So already chimps have quite a bit of encephalization even for a mammal and then humans on top of that we’ve continued that trajectory with this massive expansion. So when did that happen? And that’s what our paper kind of tries to address is we really want to look at when these changes in brain size really started which would have been at the divergence of the ancestor that Led to humans and the ancestor that ended up leading to chimpanzees. So that would have been close to 6 million years ago. But really we’re interested in the trajectory of the Australopithecines which is a very long period of time but they started out with roughly chimpsized brains and chimpsized bodies. But then the brain slowly started to get larger and larger. So it was clear that there was a selective pressure that was permitting this brain expansion to happen. Speaker 2 So then these Australopithecines, if that’s how you pronounce it, when were they roaming about? Speaker 3 So Australopithecines are a genus of organisms that existed for a long time and there are many different types of Australopithecines but the sort of crucial time window for starting To think about the lineage (Time 0:13:28)
The Evolution of the Brain • Brain size expansion started around 6 million years ago at the divergence of the ancestor that led to humans and chimpanzees. • Australopithecines had chimp-sized brains and bodies initially but brain size slowly increased over time. • Selective pressure allowed for brain expansion in Australopithecines. • Crucial time window for the lineage that led to humans started around 2 million years ago. • Approximately a tripling of brain size happened over the last 2 million years. • The expensive tissue hypothesis suggests that brain tissue is metabolically expensive. Transcript: Speaker 1 Brain size really started which would have been at the divergence of the ancestor that led to humans and the ancestor that ended up leading to chimpanzees. So that would have been close to 6 million years ago. But really we’re interested in the trajectory of the Australopithecines which is a very long period of time but they started out with roughly chimpsized brains and chimpsized bodies. But then the brain slowly started to get larger and larger. So it was clear that there was a selective pressure that was permitting this brain expansion to happen. Speaker 2 So then these Australopithecines, if that’s how you pronounce it, when were they roaming about? Speaker 3 So Australopithecines are a genus of organisms that existed for a long time and there are many different types of Australopithecines but the sort of crucial time window for starting To think about the lineage that led to humans is about 2 million years ago. Speaker 2 So we’re looking at roughly going back to what you were saying Catherine, a tripling of brain size over about the last 2 million years. Is that a fair coarse-grained summary? Yeah, I would say yeah. So central to the story you’re telling in this paper is what’s called this expensive tissue hypothesis. This is a highly influential idea as far as I can tell. And some have probably heard of it, some people may be pretty familiar with it but could you just sum it up for us? Speaker 3 The idea is that brain tissue is metabolically expensive. So (Time 0:14:02)
The Expensive Tissue Hypothesis • The central idea in the paper is the expensive tissue hypothesis, which suggests that the brain is metabolically expensive, requiring a significant portion of the body’s energy budget despite its small mass. • According to this hypothesis, in order to afford a big brain, animals may have to reduce the volume or mass of another expensive tissue, such as the gut, to balance out the energy expenditure. • The expensive tissue hypothesis highlights the trade-offs involved in evolutionary adaptations for brain development, linking brain size to metabolic constraints and energy availability. Transcript: Speaker 2 That a fair coarse-grained summary? Yeah, I would say yeah. So central to the story you’re telling in this paper is what’s called this expensive tissue hypothesis. This is a highly influential idea as far as I can tell. And some have probably heard of it, some people may be pretty familiar with it but could you just sum it up for us? Speaker 3 The idea is that brain tissue is metabolically expensive. So for us our brains use about 20% of our body’s energy budget despite only taking up 2% of our body mass. So it just takes more calories to run a brain than it does to run other parts of your body. And most animals all the time are kind of a constant risk of starvation. So if you have this really metabolically expensive bit of your body that increases your risk of dying due to not having enough calories because all those calories are getting burned Up by this big expensive brain. So the idea behind the expensive tissue hypothesis is that if you are going to afford having a big expensive brain, you have to pay for it in some other way. And so the proposition was that one way to pay for that is by reducing the volume or the mass of another equally expensive tissue in the body, which according to this idea could be the gut. So the gut also uses a lot of calories. So if you just reduce the mass of the gut, then you kind of have more calories to play (Time 0:14:59)
The Human Brain Gut Relationship • The gut uses a lot of calories and reducing its mass may provide more calories for the brain. • Having a smaller gut raises questions about how the body can still process calories effectively with less gut tissue. • The human brain-gut relationship differs from that of other primates, with humans having a lower ratio of gut tissue. • Humans have a different body shape compared to other primates, with even lean individuals carrying a significant amount of gut tissue. Transcript: Speaker 3 According to this idea could be the gut. So the gut also uses a lot of calories. So if you just reduce the mass of the gut, then you kind of have more calories to play with and can maybe spend them on the brain. But of course this brings up a question. If you have a smaller gut and the gut is the thing that you’re using to sort of digest food and bring calories into your body, something else has got to give in order to make having that smaller Gut possible. Speaker 2 In other words, how are you able to get even more calories with less gut to process them, right? Yeah. So okay, so if we actually look at the human brain gut relationship relative to the brain gut relationship in other, say, just primates, what do we see? Speaker 1 So then that’s actually how this sort of expensive tissue, how hypothesis came about was this observation that there seemed to be a different ratio of the amount of gut tissue in humans Compared to primates of a similar size. And one way you can think about this is if you look at H&Pans E or gorilla or any of our other closest relatives or the other great apes, you’ll notice that their body’s shape, especially Their abdomen, is quite round. And this is even for individuals who are very lean. And it’s really, they are holding a lot of gut tissue. They are eating a lot of really fibrous, tough leaves that require a lot, a long digestive time. (Time 0:16:09)
The Shape of the Gut in Chimpanzees Transcript: Speaker 1 About this is if you look at H&Pans E or gorilla or any of our other closest relatives or the other great apes, you’ll notice that their body’s shape, especially their abdomen, is quite Round. And this is even for individuals who are very lean. And it’s really, they are holding a lot of gut tissue. They are eating a lot of really fibrous, tough leaves that require a lot, a long digestive time. And that was another thing we were interested in was digestive time because the longer the gut is, it’s taking more time to be digested. It’s taking more energy to be digested. And further, not just like looking at the outward physical appearance, but if you were to take a picture of a chimpanzee or gorilla skeleton and put it next to a human skeleton, you’ll Notice even the shapes of like the axial skeleton have changed. So we have less flared ribs, we have a less flared pelvis. And it’s probable that they need that shape to actually encompass and support all the gut tissue that they have that we don’t have. So already we know that the total ratio is different. Now for this paper, we went further and we just, I wanted to look more specifically at what components of the gut were different because already we need all the gut tissue in general and The gut tissue that’s involved in digesting is smaller, but no one broke it down into the different components of the gut. So we did. And that’s where it really stood out for us. And that’s one of the figures in the paper of all the different components of the gut. The colon is quite reduced in humans compared to what we would expect for a primate (Time 0:17:06)
The Different Components of the Gut Transcript: Speaker 1 To look more specifically at what components of the gut were different because already we need all the gut tissue in general and the gut tissue that’s involved in digesting is smaller, But no one broke it down into the different components of the gut. So we did. And that’s where it really stood out for us. And that’s one of the figures in the paper of all the different components of the gut. The colon is quite reduced in humans compared to what we would expect for a primate of our size. So I had here with like, if I look at the gut, all the gut components in the brain, we would expect the colon to take up about 20% of that mass, but it actually takes up less than 10%, closer To 5%. Speaker 2 So sorry, when you say we would expect, you mean like, if you just take your standard average primate, right? Or great. Speaker 1 Yeah. So we would expect, okay. And just scaled it up to our size or, or, you know, right, okay. Speaker 2 So our colon is radically reduced, in other words, relative to what you would expect. Now maybe this is a good place to remind people who don’t remember their gut anatomy so well. So when you say colon, you’re referring to what are the parts of the gut that are important here? Speaker 1 Well, after the stomach, we’re especially interested in the small intestine and the large intestine and the large intestine is the other word for the colon. The small intestine is where a lot of nutrient, the first like nutrient absorption happens and where like, you know, certain enzymes and certain like bile salts will come in to almost Five fats and help break them down. But the colon does (Time 0:18:05)
The Role of the Colon in Human Health Transcript: Speaker 2 That are important here? Speaker 1 Well, after the stomach, we’re especially interested in the small intestine and the large intestine and the large intestine is the other word for the colon. The small intestine is where a lot of nutrient, the first like nutrient absorption happens and where like, you know, certain enzymes and certain like bile salts will come in to almost Five fats and help break them down. But the colon does a slower process that involves, we used to say, you know, when I was in school, I’m not going to say how well I am. They used to say, oh, a colon just resorbs water. That’s all it does. And I was like, man, that’s not much. That’s like, come on, pull your way, colon, geez. But it turns out it’s doing a lot. We have bacterial colonies in our colon. This is getting a lot more attention lately because it’s linked to so many components, human health, right? The microbiome, exactly. And so there’s all kinds of internal fermentation that are happening in the colon. Okay. Speaker 2 So that’s like the main functional job of the coal. I mean, okay, maybe it resorbs some water as you were saying, but the main job of the colon is really it serves as kind of like a fermentation station for food, right? Essentially. And so sorry, just to go back to the story about the expected ape. So what you find is that the colon specifically is what’s reduced or the whole gut is reduced relative to what you would expect in humans. Speaker 1 So the whole gut is reduced, but of that, the colon is making up the majority of that reduction, if that makes sense. There is (Time 0:19:03)
The Cost of Extra Calories • Mutations that make brains larger may be maladaptive unless the metabolic cost can be offset with extra calories. • Possible sources of extra calories for humans to offset the increase in brain size include meat eating and tuber eating. • Evidence from tooth structure suggests that tuber eating could have been another significant source of calories for early humans. Transcript: Speaker 3 Mutations that make brains larger would actually be maladaptive, would reduce fitness because they increase risk of starvation, unless you can somehow offset the cost, the metabolic Cost of having that larger brain. So if you have a way to get a little bit of extra calories in your calorie budget, then you could spend those extra calories on a brain. So it would allow mutations that make brain size larger to be adaptive rather than maladaptive. Okay. Speaker 2 So then the question really becomes, where are these extra calories that humans may have found to offset this increase in brain size? And there have been a number of proposals about this. So you talk about three main ones in the paper. I was thinking we could just quickly go through the three main ones. So a big one, initially I gather, was meat eating, essentially by turning to meat, we were able to unlock more calories. Is that right? Speaker 3 Yep. That’s been one primary idea. Speaker 2 And there’s sort of like variants of that, right? Like there’s, it could have been through hunting, it could have been through scavenging and so on. There’s also this interesting proposal that tuber eating could have been another source of calories. What’s the deal with that idea? Speaker 1 Well, I think some of the evidence comes from our tooth structure. So weirdly, human molars are a lot like pig molars and other members of that family. And they’re called bunadont teeth. And it’s actually (Time 0:21:05)
The Evolution of Our Teeth Transcript: Speaker 2 Main ones in the paper. I was thinking we could just quickly go through the three main ones. So a big one, initially I gather, was meat eating, essentially by turning to meat, we were able to unlock more calories. Is that right? Speaker 3 Yep. That’s been one primary idea. Speaker 2 And there’s sort of like variants of that, right? Like there’s, it could have been through hunting, it could have been through scavenging and so on. There’s also this interesting proposal that tuber eating could have been another source of calories. What’s the deal with that idea? Speaker 1 Well, I think some of the evidence comes from our tooth structure. So weirdly, human molars are a lot like pig molars and other members of that family. And they’re called bunadont teeth. And it’s actually like sort of disturbing how similar they look. And so people have, and because mamaologists like to classify things based on tooth morphology, they kind of pointed out early on like, hey, our teeth look a lot like a pig’s tooth or Other already adaptolids who have similar, like who root and start to tubers and those kinds of things. So interesting. Okay. It looks like some of our teeth have evolved to possibly process that. I think some of the evidence is coming from the fact that there’s hunter-gatherers that use tubers as a really important staple of their diet. That’s another reason that that has gained some traction. Speaker 2 And then last is the cooking hypothesis. So what’s the cooking hypothesis? So if you cook food, you make it easier to digest. (Time 0:21:47)
The Cooking Hypothesis • The shift that allowed extra calories to be utilized had to happen before brains grew bigger. • The timeline challenges the cooking hypothesis, as evidence of controlled fires is needed. • Early humans showed evidence of deliberate fire use, such as fire pits. Transcript: Speaker 3 Australopithecines because whatever shift happened that allowed those extra calories to be utilized that could then in turn allow mutations producing bigger brains to be adaptive, That shift had to happen before the brains were bigger. So it has to be something that’s achievable by, you know, without a large complex brain, like modern humans have. Speaker 2 So does just one, I want to get into your hypothesis in a lot of detail on this. But just one more thing about the cooking hypothesis, does the timeline work out? In other words, like, did we control fire or did we start processing meat around the time that brain size started ramping up or what, how does the time work there? Right. Speaker 1 So that’s one of the big challenges with that hypothesis. And I think the most recent is there is, so there’s the issue of how do we have fossil evidence of a fire because you can have evidence of a fire, but that doesn’t mean it was a controlled Fire. And we know that human ancestors actually would either deliberately or maybe accidentally like set fire to their entire living space in a cave, for example. And you’ll find like, I’m not an archeologist. So there’s archeologist listening. Sorry for my poor summary, but essentially you’ll find a layer of an ash lake substance that lets people know, okay, everything got burnt, which suggests an uncontrolled fire, for Example. There is evidence in, I think, for example, early humans that they had fire pits and it’s pretty clear that that was deliberately done. (Time 0:24:40)
The External Fermentation • Fossil evidence of fire does not necessarily indicate controlled fire. • Evidence of uncontrolled fire includes a layer of ash-like substance in caves. • Early humans had fire pits suggesting deliberate use of fire. • It becomes harder to determine intentional use of fire the further back in time we go. • Testing whether fire was used for cooking food is challenging. • Sparse evidence suggests fire usage even among homo-habilis. Transcript: Speaker 1 The most recent is there is, so there’s the issue of how do we have fossil evidence of a fire because you can have evidence of a fire, but that doesn’t mean it was a controlled fire. And we know that human ancestors actually would either deliberately or maybe accidentally like set fire to their entire living space in a cave, for example. And you’ll find like, I’m not an archeologist. So there’s archeologist listening. Sorry for my poor summary, but essentially you’ll find a layer of an ash lake substance that lets people know, okay, everything got burnt, which suggests an uncontrolled fire, for Example. There is evidence in, I think, for example, early humans that they had fire pits and it’s pretty clear that that was deliberately done. Now going back further, A, it goes harder and harder because it’s older and older and B, I think the fires may not have been used regularly or they may have been sporadically used. And so it becomes very tricky to make the case that if fire was deliberately set, was maybe repeatedly used, that might be something that we might care about if we want to claim that this Was an intentional act. And then was it used to cook food, which that it’s not going to be possible to really test that. Well, perhaps an archeologist is working on that. So the issue is the evidence. And my understanding, and Aaron, correct me if I think there’s been some evidence in the last years that I think it got back to even like homo-habbalists. I think there is some sparse evidence there may have been some fire usage, but our idea (Time 0:25:22)
The External Fermentation Transcript: Speaker 1 We might care about if we want to claim that this was an intentional act. And then was it used to cook food, which that it’s not going to be possible to really test that. Well, perhaps an archeologist is working on that. So the issue is the evidence. And my understanding, and Aaron, correct me if I think there’s been some evidence in the last years that I think it got back to even like homo-habbalists. I think there is some sparse evidence there may have been some fire usage, but our idea is going back into the Australopithecine so prior to that. Speaker 3 Right. So far the evidence that we have for controlled fire exists in ancestral species that were already well along this trajectory of rain enlargement. Okay. Speaker 2 So yeah, so let’s now talk about your proposal, what you call the external fermentation about. So could you say a word about that name external fermentation? What’s the idea there? Speaker 3 Fermentation generally is the process of yeast and bacteria and microbes in general, breaking down nutrients into smaller nutrients. So we all are pretty familiar with the fermentation that happens externally. Normally, we eat fermented foods and so forth. We have internal fermentation in our large intestine or colon, which we talked about. So our idea was that if you could sort of offload some of the fermentation that would otherwise be occurring inside (Time 0:26:15)
The Benefits of External Fermentation Transcript: Speaker 3 And bacteria and microbes in general, breaking down nutrients into smaller nutrients. So we all are pretty familiar with the fermentation that happens externally. Normally, we eat fermented foods and so forth. We have internal fermentation in our large intestine or colon, which we talked about. So our idea was that if you could sort of offload some of the fermentation that would otherwise be occurring inside your body in your microbiome, offload that into the environment. That could be a way to make your gut smaller, to have food that sort of semi-predagested, potentially easier to digest, have higher caloric value from the same amount of food. Speaker 2 Yeah, well, I like this framing of a sort of offloading again. So we have this fermentation chamber in our guts, but if you could do some of that outside the body, then you wouldn’t have to do so much of it in your gut. So you mentioned just briefly there, Aaron, how external fermentation can actually provide more calories, but let’s walk through it a little bit more systematically. So you talk about a few main ones in the paper. So one of them is macronutrient absorption. So what’s the idea there? Speaker 3 Plants produce carbohydrates that your body can’t digest. So these startches, complex starches, and your gut microbiome can digest them. And this can also happen with external fermentation on your countertop. So these indigestible starches (Time 0:27:10)
How External Fermentation Can Provide More Calories • The concept of offloading fermentation from the microbiome into the external environment may lead to a smaller gut, easier digestion, and higher caloric value from food. • External fermentation can help break down indigestible starches into short-chain fatty acids that can be digested by the body, making otherwise indigestible nutrients available. • Fermentation can render micronutrients more bioavailable by helping to break down anti-nutritive compounds in food. Transcript: Speaker 3 In your microbiome, offload that into the environment. That could be a way to make your gut smaller, to have food that sort of semi-predagested, potentially easier to digest, have higher caloric value from the same amount of food. Speaker 2 Yeah, well, I like this framing of a sort of offloading again. So we have this fermentation chamber in our guts, but if you could do some of that outside the body, then you wouldn’t have to do so much of it in your gut. So you mentioned just briefly there, Aaron, how external fermentation can actually provide more calories, but let’s walk through it a little bit more systematically. So you talk about a few main ones in the paper. So one of them is macronutrient absorption. So what’s the idea there? Speaker 3 Plants produce carbohydrates that your body can’t digest. So these startches, complex starches, and your gut microbiome can digest them. And this can also happen with external fermentation on your countertop. So these indigestible starches get broken down into short-chain fatty acids, and those short-chain fatty acids can be digested by your body. So it sort of makes things that were otherwise indigestible, digestible. Speaker 2 And then the second one you talk about is fermentation renders micronutrients more bioavailable. So what does that mean, exactly? Speaker 3 So food has nutrients, of course, but some foods also have what are called anti-nutritive compounds that can prevent absorption (Time 0:27:35)
How External Fermentation Can Provide More Calories • Indigestible starches can be broken down into short-chain fatty acids by gut microbiome or external fermentation, making them digestible. • Fermentation can make micronutrients more bioavailable by breaking down anti-nutritive compounds in food. • Consuming fermented foods can support healthy internal fermentation by introducing active microbial colonies. Transcript: Speaker 3 Produce carbohydrates that your body can’t digest. So these startches, complex starches, and your gut microbiome can digest them. And this can also happen with external fermentation on your countertop. So these indigestible starches get broken down into short-chain fatty acids, and those short-chain fatty acids can be digested by your body. So it sort of makes things that were otherwise indigestible, digestible. Speaker 2 And then the second one you talk about is fermentation renders micronutrients more bioavailable. So what does that mean, exactly? Speaker 3 So food has nutrients, of course, but some foods also have what are called anti-nutritive compounds that can prevent absorption of the nutrients that are otherwise present in the Food and would be available. So fermentation can break down some of those anti-nutritive compounds, and that allows the nutrients to be absorbed by your body. Speaker 2 And then a third one you talk about is that consuming fermented foods can actually support internal fermentation, right? So what is the idea there? Speaker 1 Yeah, the idea there is, and this is something, you know, I think that is maybe more widely known by the public, is that when you consume active microbial colonies, this can help seed Or maintain healthy microbiome in your own body. So we’re still, even with the reduced (Time 0:28:15)
Fermented Foods Support Internal Fermentation Transcript: Speaker 3 Anti-nutritive compounds that can prevent absorption of the nutrients that are otherwise present in the food and would be available. So fermentation can break down some of those anti-nutritive compounds, and that allows the nutrients to be absorbed by your body. Speaker 2 And then a third one you talk about is that consuming fermented foods can actually support internal fermentation, right? So what is the idea there? Speaker 1 Yeah, the idea there is, and this is something, you know, I think that is maybe more widely known by the public, is that when you consume active microbial colonies, this can help seed Or maintain healthy microbiome in your own body. So we’re still, even with the reduced colon, our microbiome is still very important for nutrient absorption and the internal fermentation processes that we do have. So when we ingest foods with live and active cultures, that can help in support and maintain that, the help of that microbiome, because that microbiome can get disrupted too, and then It can perform poorly. Speaker 2 So we were talking before about how cooking kind of unlocks calories across a broad range of foods. Does fermentation similarly unlock calories across a broad range of foods? Speaker 3 So I think the short answer is we don’t know. This research has just not been done. It seems like it might, you know, that there’s the possibility for sort of (Time 0:28:52)
Fermentation and Calories Transcript: Speaker 2 Before about how cooking kind of unlocks calories across a broad range of foods. Does fermentation similarly unlock calories across a broad range of foods? Speaker 3 So I think the short answer is we don’t know. This research has just not been done. It seems like it might, you know, that there’s the possibility for sort of broad effects, but as far as I know, a lot of that sort of food science has just hasn’t been done. Speaker 2 Okay, because yeah, and in part of your explanation, I think when we were talking about macro nutrient absorption, for example, you’re focusing on carbohydrates, breaking down carbohydrates, And so on. So I was just maybe wonder whether, you know, does fermenting meat, for example, actually do anything to us that’s helpful? Speaker 1 Yeah, we actually think I spent about a year trying to find evidence for that. And then I was pouring three journals, food science journals, which I don’t quite have in the background, but I did find some like things that were supportive. So for example, we talk a little bit about how the World Health Organization has recommendations for families that are going through famines or food insecurity that they focus on feeding Their children traditional foods that are fermented because they find it seems to maintain the weight of children better. So I found that very interesting in industrial agriculture for a long time. Grain is fermented before it’s fed to cattle, for example, because it boosts their weight gain and their growth. So to me, these were some different (Time 0:29:53)
The Effects of Fermentation on Calories Transcript: Speaker 1 So I found that very interesting in industrial agriculture for a long time. Grain is fermented before it’s fed to cattle, for example, because it boosts their weight gain and their growth. So to me, these were some different interleaved sort of sources of evidence that people sort of have stumbled upon the fact that eating fermented food seems to help with caloric absorption. Speaker 2 Right. So one little interesting tidbit in this part of the paper was you talk about how one thing that fermentation can do is that it can kind of render foods that would otherwise be poisonous, Safe to eat. It can take a food that is not a good source of calories and turn it into a food that actually is a useful source of calories. Did you say a little bit more about that? Speaker 3 One example is manioc. So this is a tuber, which contains high levels of oxalate, which make it toxic unless it’s either cooked or fermented. Interesting. Speaker 2 Yeah, I was taken by this example because I’d heard about, you know, there’s different ways, I think there’s different ways of processing manioc or cassava across cultures. And I heard about leaching and stuff. I didn’t really realize that fermentation was also part of how that’s processed, at least in some cultures, that’s interesting. Okay, so if I understand the story so far, it seems like the external fermentation hypothesis makes the argument that just in the way that cooking can help unlock calories, external Fermentation can help unlock calories. (Time 0:31:01)
The Pros and Cons of Evolutionary Biology Transcript: Speaker 2 To the obvious question. Okay, so if fermentation could have been the thing, if cooking could have been the thing that sort of kick started the process, why might we favor the fermentation hypothesis over the Cooking hypothesis? What are your advantages to this hypothesis? Speaker 3 So this is what we call an evolutionary biology, a just so story. So we’ve come up with a theory, this theory sounds great. And this is, by the way, like, many theories about how humans evolved are just so theories, like it was a plausible scenario. So what Catherine and Kristi and I did was, all right, let’s see if there’s any reason to think that this just so story might be more plausible than the leading just so story that currently Exists. And then propose a bunch of ways to test it. So we can get to that maybe later. So one is that Australopithecines, though, the organisms in question here that would have had to evolve this new method of unlocking calories to a level that would allow brains to begin To expand, they have chimpanzee-sized brains. So Australopithecines aren’t chimpanzees, they’re not identical, but chimpanzees might be a good modern proxy for the types of behaviors that Australopithecines may have been Capable of. And we both worked with chimps and other living great apes, and we both just kind of scratched our heads at the idea of chimpanzees, like reliably controlling (Time 0:32:49)
The Evolution of Caching • Caching behaviors observed in many different mammals, indicating it may not be cognitively difficult. • Sharing food among humans may have involved more communal storage and sharing compared to other primates. • Social and emotional shifts likely played a role in the development of caching behaviors among early humans. Transcript: Speaker 3 Going to ferment whether you want it to or not. So that was our thought, was that they have started accidentally and had been a sort of unavoidable byproduct of caching. Interesting. Speaker 2 So yeah, I did want to drill into this caching idea. Do we know that humans or Australopithecines, rather, were capable of caching or were doing some caching like behaviors? Or what reason do we have to believe that they were already capable of caching, I guess, is the question? Speaker 1 That is tricky. I would say, first of all, we see caching behaviors in many different mammals. It’s a very common way to deal with if you have some extra food, including rodents are capable of caching. So we feel that cognitively it’s not difficult. In terms of evidence for it, that is where things get a bit tricky. Speaker 2 I guess what I’m wondering is, granted, caching doesn’t seem like a very sophisticated behavior. As you mentioned, a lot of mammals do caching. But other primates don’t do caching. Speaker 3 So I’m wondering, I guess, there’s some idea that humans had started caching for some reason, and then that could have… I think one thing is that with most other primates, sharing food is sort of a matter of tolerated theft or allowing someone to eat next to you without trying to steal their stuff, rather Than having a communal location where food is stored and shared. So that would rely on some social and emotional shifts that might have been present before this type of behavior (Time 0:34:35)
Fermentation is versatile in technique and conditions Fermentation can be done on various foods such as shellfish, vegetables, fruits, meats, and even different parts of animals, regardless of climate. The process can occur in different environmental conditions - open, closed, or submerged in water. Surprisingly, the wide range of techniques and conditions for fermentation makes it a versatile process that does not always require meticulous care. Transcript: Speaker 1 I would just add on a practical level. When I first, when the early days of thinking of this, I was kind of like, well, so many things are now fermented and cave. So I was like, well, this makes perfect. Well, A, it’s kind of australopithecines. There were several species and I don’t want to make a claim about where they typically lived. But I also, as I researched this paper, because I wanted to see if I can find commonalities in what you need to ferment to food, to see if I could drill down on like, what would be the original Conditions where the eureka we ferment and something. Well, it turns out the variety of techniques and environmental conditions blew me away. So you can ferment and that’s why I have that obnoxious table that no one will ever read because it’s enormous. Speaker 2 I read it. I read it. Speaker 4 Did you go, gosh, bless you. Speaker 1 That was, I think that was like my entire like, 2018, that was my Saturday. So it’s because I kind of thought, well, there’s got to be things you can’t ferment and no, you can ferment shellfish, which I thought would kill you and you can ferment any kind of vegetable You can think of, obviously fruit, all kinds of meats, but even organs, different parts of the animals, bodies, et cetera. But on top of that, it occurs in all different climates. So the temperature wasn’t as crucial as I thought it was. And then open, closed or submerged in water, those are all possibilities. So it doesn’t have to be something that’s cashed in a careful way that you dig a hole, put it in. (Time 0:40:18)
Comparative Study on Different Diets and Metabolic Indicators Comparing metabolic indicators over a fermented diet versus cooked diet, and a raw diet could provide insights into caloric balance and microbiome changes. Research shows that fermenting meats in certain climates can make vitamin C more bioavailable, aiding in nutrient intake for communities with limited plant matter. Transcript: Speaker 1 Well, I have one that I don’t know how practical it is, but I would really like to be able to get a group of people who would be willing to try different diets over the course of a year. I mean, I had to, I’d have to also look into how long. But basically, I’d want to compare basically metabolic indicators over the course of a fermented diet versus a cooked diet, but no fermented food and perhaps a raw diet that could be Illustrative too. But I’d really like to compare fermented to foods that are not fermented and see if it changes their caloric balance, what it does to their microbiome. I actually was contacted by someone in England who travels occasionally to Greenland and he’s been working with a physician in London to look and unfortunately, it’s an end of one. That’s the only problem. But he went over there and he went to Greenland and he just kayaked everywhere and he only ate meat basically. He ate a very indigenous diet. A slight aside, that’s another interesting thing is that fermenting meats in those kind of climates permits vitamin C to be available, bioavailable in a way that it’s not. And so there’s some interesting research showing that that’s how those communities adapted to living in an environment with very little plant matter. They basically were fermenting their meat and that gave them some of the nutrients that they wouldn’t have otherwise gotten. But anyway, he has a metabolic indicators when he came back from basically eating like a mainly fermented fat diet were fantastic. Interesting. So he’s going to go back, but he was he was he was doing a lot of kayaking. So he said, yeah, so I’m just going to go back and not do any exercise and just do the diet. (Time 0:46:10)
Evolution of Preferences in Primates The discussion revolves around the idea that preferences for fermented foods in other primates could be linked to the external fermentation hypothesis. It is suggested that the ability to prefer cooked or fermented foods may not necessarily indicate human evolution but could be a latent preference that was capitalized on. Observations of chimpanzees consuming fermented palm juice and the existence of the ‘drunken monkey hypothesis’ are mentioned. The gene for alcohol dehydrogenase, responsible for metabolizing alcohol, appeared early in evolution, before Australopithecines, challenging the timing of the evolution of preferences for fermented foods. Transcript: Speaker 2 So yeah, and this connects to one of the ideas that you mentioned, Katherine, like you mentioned you would want to actually see if there were preferences for fermented foods in other Primates. So just to briefly revisit that, was your thought that if the fermentation external fermentation hypothesis is on the right track, then you wouldn’t see preference for fermented Foods in other primates? Or what was your thinking there? Speaker 1 Well, my thinking, that was tricky because I think you could make the case either no matter what result you get, you can say, well, you see, we evolved, you know, or you could say the so The people who were doing the cooking thing, when the apes prefer the cooked food, they said, ah, see apes prefer cooked food. It’s just humans evolved the capacity to do it. Oh, I see. I see. Speaker 2 So there was a latent preference that then got capitalized on that kind of I see. So yeah, you can now I will say we. Yeah. Speaker 1 Yeah. And then I will say that, you know, we’ve observed chimpanzees in the wild consuming my think it’s fermented palm juice, which farmers will ferment like collected and it ferments on Its own. And it’s good for their purposes, but the chimps have discovered it and will ingest it. Right. And it’s going to be attracted to at least fermented sugar compounds in a certain some kind of fruit. Yeah. Speaker 2 Yeah. I was going to actually ask about that this so-called drunken monkey hypothesis is one that you touched on in the show before. So how does the drunken monkey hypothesis square with your external fermentation hypothesis? Speaker 3 If it does, well, so the gene for alcohol dehydrogenase, which is the enzyme that metabolizes alcohol, that appears much earlier in evolution than we’re talking about. So the ability to break down alcohol into digestible sugars appeared before Australopithecines. (Time 0:51:51)
Evolution of Alcohol Metabolism and Fruit Consumption in Primates The gene for alcohol dehydrogenase, responsible for breaking down alcohol, evolved early in evolution before Australopithecines. Existing apes and primates are attracted to fermented fruit. While the taste of alcohol differs from other fermented foods, fruit could have been a valuable seasonal resource for Australopithecines due to its abundance and appeal to primates’ evolved ability to detect ripe fruits. Transcript: Speaker 3 If it does, well, so the gene for alcohol dehydrogenase, which is the enzyme that metabolizes alcohol, that appears much earlier in evolution than we’re talking about. So the ability to break down alcohol into digestible sugars appeared before Australopithecines. And as Catherine mentioned, like other existing apes and also other primates in general will sort of capitalize on fermented fruit when they find it. Speaker 2 So how would you weave that into the story? Oh, is this just a separate thing? Speaker 3 I think it’s separate. Me personally. I don’t know. Speaker 1 What do you think, Catherine? I think it could be similar. And I think it could be different. The taste of alcohol, if you want to evolve the preference, it’s different from the sour taste that you get from a lot of fermented food. And it’s different from the cheesy flavors you might get from other kinds of ferments. So, but on the other hand, as we were speculating, if at some point in the Australopithecine evolutionary journey, they started cashing food in some way or storing food in some way. Fruit would be a very good thing to cash because it’s exactly this sort of seasonal resource that you were not going to be able to exploit all of it. It’s going to have this abundance and then it’s gone. So that would be something, a prime candidate. Another reason that fruit to me might be an important part is just because primates seem to be really specialized for detecting ripe fruits early in primate evolution. There’s even modifications to receptors in our eyes that distinguish green and red more readily than many other mammals. (Time 0:53:09)