Curtis W. Marean

How did modern humans evolve into modern humans?

Modern humans have a unique psychological and cognitive machinery that evolved in the late Middle Pleistocene. Paleoanthropologists have focused on climate and environmental change as the driver for much of human evolution. While this might be a productive paradigm for explaining earlier phases of human evolution, it fails to explain the final steps to the evolution of modern humans. The evolution to modern humans involved a shift out of the high mobility-light technology niche to one focused on dense and predictable resources with a consequent reduction in mobility and increased complexity of technology and human social relations.

FULL TRANSCRIPT 

Those of you who know my work know that I direct a project, a multidisciplinary project on the South Coast, and Pinnacle Point is one of the localities that we work at and we do all the things that you've been talking about, isotopes, fauna, stones, we even do tephra, right? We found Toba and the sites that we published back in 2018. But I'm not going to talk about any of that. I'm going to give a theoretical talk and I want to thank Rob Foley for being the first person to get up and give a talk like that. It's probably almost as dangerous as jumping into a wood chipper. 

And I'm going to talk about culture and how culture is probably the primary driver of the last key phase in human evolution, which is the transition to people like us. So in the talk, what I'm going to do is I'm going to ask the question, what do we mean by a modern human? Because I think we've got some confusion in that area. I'm going to talk about the significance of what I'm going to call the modern human triad, which has three parts, hyper-prosociality, a slavish reliance on social learning and modern human cognition. I'm going to explain why I think climate change is not the driver or is an insignificant driver of the evolution of the triad. And then I'm going to argue that the final step to modern humans must've been caused by cultural change, not climate change. 

So, we have Homo sapiens and modern humans, and they're not necessarily the same thing. So, Homo sapiens are defined by anatomical features that fall within the range of variation of modern humans. But modern humans are defined by psychological, emotional, and cognitive characteristics that fall within the range of modern humans. And given that we can assert that it's possible even likely that there were populations of Homo sapiens that were not modern humans in the late middle Pleistocene and late Pleistocene. And we can also come to the conclusion that modern humans must have been a population of Homo sapiens. They must have evolved in Africa, and they must have evolved before 70,000 years ago or before the great human diaspora, before modern humans left Africa. These are kind of assertions that we can deduct from some very specific points. So, Homo sapiens is defined by anatomy, there's lots of people in this audience that know a lot more about that than I do. 

We've heard a couple of talks, but most of the features that people use aren't related to the way that we define modern humans. They're not related to psychological and emotional and cognitive features. But back in 2018, I read this very interesting paper by Neubauer et al., and it's one of the few that really possibly makes a connection between anatomy and those things that we need to use to define modern humans. And that's the origin of the globular brain case, which they argue, they co associate it with the evolution of a modern human cognition. So that possibly is an anatomical feature that we can think of. So let me dig a little bit more into what I'm saying is the definition of modern humans, an innate proclivity to cooperate at very high scales with unrelated individuals is what I mean by hyper-prosociality. And what we're doing right here is hyper-prosociality. 

We're getting together with unrelated individuals sharing information. It's costly, it's et cetera. It's really hard to explain that the evolution of that behavior with animals, an innate slavish reliance on social learning through high fidelity copying behavior, I'm not going to talk a lot about that, but if you've had kids, you know what I'm talking about. And then the most advanced organic ability to acquire knowledge and understanding, that's what we often call an advanced cognition. I think we probably just want to say the way we understand it, it's a modern human cognition. That's what we have among all living people today. So I call that the modern human triad. That's the three features in a sense. I'm using them like anatomical features, but they're behavioral. 

And when we take a modern human cognition and we add it to that special psychology for social learning, and we then add onto that extreme cooperation, what we do is we create the capacity for modern human cumulative culture. That's our unique adaptation that allowed us to spread out of Africa and start to make our way into outer space. And that no other animal, no other extant animal has that, that's unique to us. And we need to explain how it came to be. So these three capacities and proclivities, they're embedded in the genome. They're evolved just like anatomical features. Therefore they are subject to evolutionary explanation, just like all the things we've been talking about. So that gives us a great research question when, where and how did the modern human triad evolve? And like I've asserted, climate change is insufficient, and I think I can make a good case for that going forward. 

So modern human cognition, you already know pretty much what that is. Extraordinary ability to acquire and process knowledge, store it inside and outside the mind, retrieve it and use it. Creativity is a part of it. Ability to use analogy, right? Symbolic behavior. And this one has received a lot of attention in the archeological literature. So if you go through what we've been doing in the middle of stone age for the last 40 years, we're always talking about cognition, but I think we've put too much emphasis on it. It's important, but the triad is more important. 

So extreme cooperation, what I've just used the word hyper-prosociality. This is an emotional complex of us-ness. Groupness, right? It's the foundation of tribalistic, nationalistic feelings. And boy do we see them on the rise today. They have good things about them and they have really bad things about them. It allows high levels of cooperation with non-kin. And I think really importantly, it allows a special form of cooperative breeding. And there's lots of different kinds of cooperative breeding. But what I mean is formal made exchange, what we call an anthropology reciprocal exogamy, that is the foundation of multi-scale sociality and extended social networks, which allows us to form ethnolinguistic groups and tribes, which again is unique. So to give you an illustration of how this works, chimps have no hyper-prosociality and they have single level sociality. So chimps live in troops, what we call troops. If they were humans, we call those bands. And at the contact of those troops, they have conflict warfare as was first documented by Jane Goodall. Modern humans are very different. We have hyper-prosociality, which allows multiscale society. So we live in troops slash bands, but formal maid exchange, reciprocal exogamy ties those troops or bans together and unites them into ethnolinguistic groups. And it's at the boundary of those tribes that we see conflict. It's very, that's what we mean by multi-scale society. This is the original universal human social structure. And if you want to read a great scholarly treatment of it, Bernard Chapais 2008 book, Primeval Kinship is just a home run. 

So 2015, I think it was Richard Leakey's 70th birthday. I was so, so lucky to be invited to go to the Royal Academy and give a talk in honor of that. Thank you so much. It was a highlight of my life. And I gave a talk on the first part of this talk. And what I argued is that late in human evolution, the addition of dense and predictable resources was a fourth dietary revolution. And it created set up a selection regime for hyper-prosociality. And that eventually led to the great human diaspora. And I published a paper in the special issue that came out of that. So, basically the hypothesis that I argued was is that hyper-prosociality evolved uniquely and the modern human lineage among modern humans. So it's the modern human derived condition. And when hyper prosocial, multi-scale societies come into conflict with single level societies, they always win because they can put more warriors in the field, and that results in the extinction of single level societies. 

So my hypothesis was that Neanderthals retained the original primitive form, very low or no hyper prosociality, single level society like chimps. And when modern humans came out of Africa, Neanderthals and all the other megafauna and so on didn't have a chance and humans spread across the world, they killed all their competitors, and of course killed the top of the food chain. That's why we see megafauna extinctions. So why is climate change insufficient to explain the evolution of the triad? So to make this argument, I'm going to summarize an enormous amount of theory and comparative ethnography and draw primarily on theory that we call human macro ecology, human behavioral ecology, standard comparative ethnography from cultural anthropology and evolutionary psychology. So I'm going to blow through an enormous amount of material, but it's published in some of those papers. But first I just want to ask the question, what is behavioral and cultural complexity? 

We have a technological realm, that's the number of parts and raw materials that make up a tool. We have a social realm, that’s the amount of economic and political differentiation. We have institutional realm, that's the number of rules and regulations and norms that are structured in society. And of course, we are super complex societies with thousands and millions of these things and other societies range and variation in that. So, among hunter gatherers, we have very complex hunter gatherers like these Inuit and Tlingit. Tlingit are northwest coast hunter gatherers. Their diets are normally aquatic plus terrestrial. They're just aquatic sometimes. They have lots of storage. Their technologies are heavy, they have very few residential moves. Sometimes they live all year in villages. Band sizes are large a hundred people or more. They live in small, tightly packed societies. They're non egalitarian, so they're stratified sometime even at the level of chiefdom. And warfare is typically very high. Non-complex hunter gatherers that dominate the tropics. All of Africa, their diets are normally terrestrial plants and animals. They show little and short-term storage. The technology is very light. Everything can be carried by one person. Residential moves are many. They move about 10 to 50 times a year. Band sizes are small. Territory sizes are really large. They're usually egalitarian, and they have, which means they have little social differentiation. Everybody's equal and warfare levels are low to non-existent. 

So on this graph, I'm just going to show you one example of how we drive up complexity. Each dot is a tribal group. It's an ethnolinguistic group. On each of the graphs on that Y axis is increasing technological complexity. It's a measure called techno units. It's just the number of parts and raw materials that make up a tool. So, as you go up, it's getting more complex. On that Y axis is effective. Temperature was a proxy for seasonality. And in that box we have Africa, it's warm, no snow, very, very warm. A seasonal environments. Those are the colder environments. That's actually where Neanderthals would be living. So colder swings between winter and summer, high temperature latitudes or high latitudes. On that axis, we have the percentage of diet that is fishing or shell fishing, so percentage aquatic. Now, if we take all of the African climate variability over time, which we've heard tons about over the last few days, it never gets outside that box that you see there, never, even during glacial phases. 

So in Africa, there is no climate change that would drive hunter gatherer complexity above that tropical adaptation that I just talked about. What that means is, is that climate could never have driven hunter gatherers in Africa to be complex hunter gatherers. It cannot be, it's off the table, at least what we know from data and theory. The only way the only game in town is to add aquatic resources to the diet. That's the only way you ratchet up complexity among hunter gatherers societies. So why do aquatic resources cause complexity? They're dense and predictable resources. Almost always, they trigger warfare. The hunter gatherers fight like crazy when they become aquatic hunter gatherers. That's documented in animal ethnography. It's documented in a comparative ethnography, and it's supported by one of the most powerful theories in behavioral ecology called the theory of economic dependability. It reduces mobility. It often requires more complex tools and reduced mobility allows you to make more complex, heavier tools so you get a feedback mechanism. 

So the more you reduce mobility, the bigger complex technology you can get, and then you can be more and more sedentary and it drives populations up. So in Africa, fishing and coastal foraging are the only pathways to hunter gatherer. Higher complexity In Africa, fishing, systematic fishing, particularly the big fish, requires complex technology. But using the intertidal zone does not. All you need to be able to do is figure out the relationship between lunar cycles and tidal rates. And I've published extensively on that. And if any of you live near the ocean, you know what I'm talking about. So when do these occur? Systematic coastal adaptations in South Africa date all the way back to 160,000 years ago. And Pinnacle Point is still the first site, the earliest site that we have for systematic coastal foraging In North Africa we have a broken record, but there seems to be around 110,000 years ago, a commitment to coastal resources. And then it really kicks in 25,000 systematic Riverine Lake adaptations, Sahara and Nile Valley after 25,000 central Africa, east Africa. It's all pretty consistent there. But there is the one observation at Katanda published back in the 1990s where they have fishbone, middle stone age, really old OSL dates. I mean old in a sense that early on in the development of OSL. And I'm going to assert that we need confirmation that needs a validation study to see it. 

So I think our first foray and to the dense and predictable resource zone occurred in South Africa 160,000 years ago to 125,000 years ago at the origin point of what I would say would be the transition to a truly modern human as defined by the emotional and psychological complex that has to be in place to be one of us, to be able to operate in a society like we have. And many of you have heard me coming around and pestering you about do you have fishing sites in the middle stone age? That's why I'm so interested in those. We need to do research on that topic in East Africa because East Africa is the places where we're going to see it because they have really rich, potentially rich fishing cultures. So I'm just going to summarize the big story is the way I see it. What I've been listening to for the last four days, which has been absolutely fascinating, and thank you so much for the crash course on Turkana, is this, from 3.5 million years ago to 200,000 years ago, we had a tropical terrestrial hunter gather, a little bit more ape-like early on, a little bit more modern humanlike, a little later focused on terrestrial plants and animals. 

There was very little storage light technology was very light carried by one person. Eventually they invented bags and so on to carry a few things, a lot of residential moves moving the camp and the family, small band size 20 to 30 large territories. But this is a key thing, and no one's been talking about it, but this is an absolutely essential evolutionary step. We know that the shared common ancestor had to have the primitive ape stratified society like chimps, but tropical hunter gatherers are egalitarian and they have all these really complex cultural rules for leveling people to keep it egalitarian. When did that evolve? That's a breakthrough. I don't know if we can get that from the archeological record, but we certainly need to be thinking about it. And that probably happens as a tropical hunter gatherer. But here's my point. Modern humans are psychologically and cognitively over-engineered for that niche. We inhabit it effectively, but we're over-engineered for it. And those things that we have, that brain size and the emotions and so on, it's costly and you wouldn't evolve it unless there was some selection regime for it. 

So that niche cannot be the evolution of modern humans. So, the evolution of modern humans requires a cultural niche of greater complexity, increasing reliance on aquatic foods, which will trigger increasing sedentism increasing technological complexity, increasing social and institutional complexity, increasing warfare, which is unfortunate, but it just happens. And that sets up the selection [00:20:00] regime for hyper-prosocial psychology and selection for high levels of complex social learning. So the hominid adaptation at that time was a consistent reliance on tropical terrestrial food niche that results in a very slow ratcheting of the cultural niche. The slow ratcheting of the cultural niche drives slow cognitive increases, slow cranial increases. That's what we see with early Homo and Homo erectus. The slow ratchet of cultural niche drives slow shifts in the form of social learning toward the modern human form. And at 300,000 years ago, we have a Homo sapiens like Jebel Irhoud, large brain moving to a globular form, but in my opinion, still retains the primitive ape form of low prosociality and lack of multi-scale society troops do not drive. Final steps. 

That slow evolution of a complex cognition eventually allows people to break into the dense and predictable food niche that creates the selection regime for aquatic hunter gatherer adaptations and hyper prosociality and complex social learning. Eventually that blossoms into the formation of tribal social structure, multi-scale social structure, and all the complex tools that come with it that get added to that. And that then triggers the great human diaspora. So my conclusions are modern humans are defined by the modern human triad, anatomy's part of it, but it's not the key part of the final move. These characters are evolved psychological, emotional, and cognitive characteristics, and they require evolutionary explanations, just like anatomical features. Climate change doesn't make it as an explanation for this. It had to be a cultural change. And I think the most parsimonious cultural change would be a shift to dense and predictable resources that drove the last steps to modern humans. And in recognition of that, I'm happy to say that in March we just submitted a World Heritage nomination and we called it the Cradle of Human Culture for the modern human origin sites in South Africa. And Pinnacle Point is one of the main sites in that it's a serial nomination as one of the main sites. So, I want to thank my friends and colleagues and TBI so much for inviting me to this wonderful conference and all the other my team in Mazel Bay and my supporting grants and staff. So thank you very much.

 

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