Comparative Brain Evolution: Mammals, Primates & Humans | Robert Barton | #171

About the guest: Robert Barton, PhD is an evolutionary anthropologist and Professor at Durham University. He studies the evolution of the brain and behavior across species, including humans. Episode summary: Nick and Dr. Barton discuss: mammalian brain evolution; how brain and body size scale across mammals; how metabolism relates to brain size and function; the evolution of the neocortex & cerebellum in primates & humans; the concept of “intelligence” and whether it relates to brain size; and more. Related episodes: * Evolution of Complex Behavior, Perception, Cognition, Consciousness & the Brain | Paul Cisek | #107 * Organisms, Cities, Companies & the Science of Scale | Geoffrey West | #12 *This content is never meant to serve as medical advice. * Support M&M if you find value in this content. * Full audio only version: [Apple Podcasts] [Spotify] [Elsewhere] * Full video version: [YouTube] [Odysee] * Episode transcript below. Full AI-generated transcript below. Beware of typos & mistranslations! Robert Barton 3:42 Yeah, so my name's Rob Barton. I'm an evolutionary anthropologist, but that means that I have a pretty diverse background. I started in zoology, but also did psychology, and have always been interested in the kind of intersection between those two disciplines. Went on to do biological anthropology for a masters, and started to get interested in questions to do with the evolution of the brain. And I've been, you know, I've resided in psychology departments and interacted with cognitive scientists and neuroscientists, but wound up in an anthropology department, and that's really why I call myself an evolutionary anthropologist. It's a matter of taste as much as anything else. But broadly, I'm interested in evolutionary theory and what it can tell us about the evolution of our own species, but particularly in relation to the brain and cognitive abilities. Nick Jikomes 4:51 Yeah, I actually started out myself. I was a zoology major in college, and I was studying evolutionary biology and. Before I went into neuroscience. And one of the things that I value a lot about that kind of educational trajectory is when you study Comparative Zoology and evolutionary biology and evolutionary genetics, you really it really teaches you. It taught me at least the value in the comparative approach, that even if you're interested in humans, say you can actually learn a lot by studying other creatures and understanding how and why they're different, and that's very much what you seem to do. So we're going to talk about a lot of different species and comparative biology here, but I think a lot of it will be anchored in the human brain and understanding humans. What I wanted to start out with is a very simple question, how big is the human brain in absolute terms and compared to other creatures? Robert Barton 5:47 Well, it's not necessarily the largest brain in absolute terms, because there are whales that have larger brains, but in relative terms, it's generally considered, when you take account of the overall size of the animal, relate the size of the brain to the size of the body that amongst currently living species and any fossils that have been discovered so far, humans have the largest brains relative to their body size. So if you compare us to our phylogenetically closest relatives, the other great apes, such as chimpanzees and gorillas, our brains about our bodies are not that much different. In fact, we're smaller than gorillas, but our brains are up to about three times larger. So something happened in this sort of approximately 7 million years after the divergence of the hominin line leading eventually to us on one hand, and the line that ended up in modern living chimpanzees, something pretty unusual happened On the branch leading to our own species. Nick Jikomes 7:02 And if we look at all of the fossil humans and pre humans, between the divergence from chimpanzees up until present day, Homo sapiens was was the increase in cranial volume and brain size? Was that uniform? Was it non uniform over time. I often hear things not necessarily from scientists or anthropologists. People often say things like, the human brain doubled in size in a million years, a sense for what did that tempo of change look like? Robert Barton 7:31 I mean, that's a really good question, and one which is still being debated. And actually, my co authors have a paper under review at the moment that has something new to say about that, so I can't really talk too much about that, but in general terms, what we see when we look at the hominin fossil record reflects what we see when we look more broadly across the Tree of Life, which is that the tempo. Patterns and tempo of evolution are tremendously variable. So you don't see a single kind of uniform pattern. You see variation in rates of change at different things happening on different branches of the tree. And you know, we've, we've tended in the past to think of human evolution, certainly about when I was a student, you know, the story was pretty simple. You had a few Australopithecines, and then the advent of our own genus, the genus Homo and then eventually, sort of archaic homo sapiens. And the things were, you know, just kind of increasing, changing gradually over the last 7 million years in a fairly sort of linear sort of way. But now the fossil record is so much richer what we have now, we can see that there were lots of different things happening on different branches of that part of the tree of life and brain size, you know, didn't change much initially, but it then started to expand quite rapidly. And so the overall pattern that we see is one of accelerating increase towards the present. So and that's kind of suggestive of some kind of positive feedback process. We don't really know why though there was escalating acceleration in increase in brain size, but it is consistent with ideas about positive feedback of some kind, for example, possibly between between cultural change and biological change, some feedback between biology and culture. But we've also now, we've also just just quickly. We've also now got. Fossils that tell us that, you know, none of this was uniform. So there are relatively recent hormones with small brains, and possibly we see brain size reduction happening in some lineages. So there was nothing kind of inexorable and inevitable about the pattern. It was tremendously variable. And that's one sort of big lesson that over my career, the data has taught me, is that patterns are very complicated. Nick Jikomes 10:32 Yeah, yeah. So different patterns on different branches, even the pattern presumably changes on the same branch at some point, if you just look long enough when you say a positive feedback mechanism that accounts for this sort of accelerating increase in brain size in our lineage. I understand that we may not know exactly what that is, but in principle, what could that look like? Would that be? Would one way to think about that be like? Maybe there was selection, for some reason, for a larger brain this sort of unlocked our ability to have richer social interactions and develop a richer culture, which then creates a social additional selection pressure for an even larger brain. Would that be like one way to start thinking about that? Yeah, Robert Barton 11:13 and that is the kind of classic Machiavellian intelligence hypothesis, kind of arms race in socio cognitive abilities. You know, the smarter the other individuals in your group are, them, the smarter you need to be. And, you know, and that's one possibility. For many years, the so called, sort of social brain hypothesis really held sway. It's been somewhat more questioned in recent years as a kind of the explanation of everything, but it's a distinct possibility that social life was a really important factor in the evolution of the brain, and it could that kind of feedback could account for the acceleration we see on the hominin line. But, yeah, we … This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit mindandmatter.substack.com/subscribe