What role did culture play in human evolution? Why did human brains get so big so quickly? When and why did inequality first emerge in human society? Harvard professor and author Joe Henrich picks some of the best books for understanding 'cultural evolution.'

What exactly is ‘cultural evolution’?

In the last 20-30 years a lot of different disciplines—I have psychology and economics particularly in mind, but also parts of biology—have become increasingly convinced that, in order to understand humans and human behaviour, we need to take culture seriously. Economists have recently got into this, and they now have quite a bit of evidence that, in order to explain the differences among, say, the wealth of nations or innovation or growth in GDP, culture matters a lot. These sets of ideas, beliefs and values that people acquire from prior generations really have a big impact.

Then the question becomes, how do we think about this in a systematic way, because culture is notoriously fuzzy. What my colleagues and I have tried to do is to think about culture as an evolutionary system. We can think about how individuals learn from each other, right down to a child growing up: Who do they pay attention to? Who do they learn from? What kinds of ideas are they attracted to?

“Genetic evolution is shaping us to be cultural learners, but then the interesting part is that that turns around, and cultural evolution begins to shape our genetic evolution.”

So, in my book, what I try to do is approach that from an evolutionary perspective. Humans are a kind of animal, and we seem to be very dependent on culture and cultural learning for very basic things — like how to find food, how to organise our societies, how to make the basic tools which allow us to survive. We can think about culture as a genetically evolved cognitive adaptation for learning from other people. Natural selection is operating over generations to make people better at learning from the other members of their social milieu — figuring out who in their environment they should tune in to, what kinds of ideas they should pay attention to, and how they should integrate information across diverse people.

This turns culture into an evolutionary process that can change over long periods of time; that can reach stable states — the way genetic evolution will produce stable species for long periods. It creates clumpings or groups — where some people tend to do things one way, and other groups tend to do things in other ways. It creates something called ‘social norms.’ Once people can culturally learn the standards by which they judge others, you get social norms out of this process.

Genetic evolution is shaping us to be cultural learners, but then the interesting part is that that turns around, and cultural evolution begins to shape our genetic evolution.

How?

Say something simple like the evolution of technology: you begin to produce fire and cooking and knowledge about how to process plants and animals, how to cook meat. This then shapes our digestive system: we have small stomachs and small teeth and short colons because we’re the cooking animal, or the food-processing animal more generally. A lot of our digestion is actually done externally — so we have to put much less energy into our digestive system. This is because we have all this culturally learned know-how about how to process foods.

Why does the term ‘cultural evolution’ seem to be somewhat controversial, then? Is it that some scientists, focusing primarily on genetics, feel that culture doesn’t have a role to play in evolution — just as, I suppose, some economists also would argue that straight economics doesn’t need any inter-disciplinary input either?

One interesting thing about the sociology of the field is that in the 1970s, when socio-biology first began to emerge and try to apply evolution to explain human behaviour, the culture wars emerged. One side would insist that human behaviour is determined by culture — so there were anthropologists like Marshall Sahlins who wrote a book called The Use and Abuse of Biology. On the other side, people like Richard Dawkins argued that genetic evolution played an important role in explaining behaviour and human behavioural variation.

“Tools and social institutions and languages shaped our genes.”

What’s interesting about the approach that my colleagues and I have been working on is that it actually dissolves that unhelpful and—I think—scientifically destructive dichotomy. We say, ‘Yes, culture is important. But to understand the foundations of human learning, we need to think of ourselves as an animal with adaptations for learning from others.’ Then we can say a lot about cultural evolution and about how societies evolve and what kinds of things we should expect of the world by understanding how natural selection has shaped our minds to make us better learners. That single move diffuses the difference between culture on one side and genes on the other.

The interesting thing that comes out of this is the idea that culture can actually be the driving force in human genetic evolution. I argue in my book that the central driving force in human genetic evolution—that gave us big brains, shaped our hands and dexterity as well as our feet and other parts of our anatomy—was actually created by cultural evolution. Tools and social institutions and languages shaped our genes. That idea—that genetic evolution was driven by cultural evolution—is relatively new and certainly hasn’t been widespread until recently.

And some people might disagree. Are you finding a lot of resistance to the idea?

Of course there is disagreement, there is always going to be disagreement. One of the central lines of this disagreement is how important this learning process is versus what some evolutionary psychologists call ‘evoked culture.’ This is the idea that our minds are like jukeboxes and respond to environmental cues. When you have certain environmental cues, you get different behaviours and different psychology. It’s not because people learn different things from previous generations: instead, it is just their minds responding, in a pre-programmed way, to different input cues.

For example, some people have argued that personality types—introversion/extroversion—are a product of the pathogen environment. In environments high in pathogens, people are nervous about strangers who might carry pathogens, so they become more introverted, more xenophobic, less willing to engage with others. But once the pathogens are removed from the environment, then it is much more beneficial and adaptive to interact more broadly with large social networks because you are less likely to get pathogens.

The case that I’ve made is that both of these are important. A lot of times the environment, the things that cue up these different psychological processes, are themselves influenced by cultural evolution. In the case of the pathogens—if you buy that account and there is at least some evidence for it—you have to take into account that there’s been massive cultural evolution to reduce the pathogens in our environment. There used to be malaria in southern England. But because of institutions, now there’s not. So that changes the pathogen environment in ways that then shift this evoked psychology. That’s one of the points of debate: where is this evoked psychology, what role does it play, and how important is it?

So you’re working with academics from all sorts of different fields: anthropology, archaeology?

Part of the programme here is that the way the social sciences are divided up doesn’t actually make much sense. So, for example, if you want to study economic behaviour, you can study it in economics, or in economic anthropology. There’s a field called economic sociology. Psychologists study economic decision-making. And you get quite a different picture of how people make decisions and the importance of economics depending on which of those social science disciplines you are in.

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We say, let’s create a richly pluralistic set of methods that use the ethnographic methods of anthropologists, the behavioural, psychological experiments of psychology and behavioural economics, the systematic and rigorous statistics that are best drawn from economics and put all that together, and try and build a single coherent picture of human behaviour that’s rooted in what we know about evolution, but takes seriously the fact that we are a cultural species and that lots of our ability to adapt to our environment and how we respond depends on those things we’ve learned from prior generations.

Will this understanding impact the future and, say, help solve world problems?

One thing I develop in my book is the notion of the ‘collective brain.’ A lot of work on human innovation has assumed that innovation and invention are a product of singular geniuses who racked their brains and came up with ideas. So if you look at how economists think about energising innovation, they often want to increase the incentive to inventors, so beef up the patent laws or create some way in which inventors can make more money on their inventions.

“If you really want to energise innovation, you should create larger collective brains — in other words, interconnect more minds and allow information to flow more freely among people with diverse areas of knowledge and expertise.”

What I argue is that human invention has always been a product of the interaction of minds. Cultural evolution moves faster and we produce more innovations and better adaptive bodies of knowledge when individuals are, through luck or through their own insights, generating ideas, but then these ideas can rapidly recombine with other ideas. I lay out evidence in my book that larger and more interconnected societies produce faster cultural evolution and have fancier tools. So, if you really want to energise innovation, you should create larger collective brains — in other words, interconnect more minds and allow information to flow more freely among people with diverse areas of knowledge and expertise.

Read 1 The Selfish Gene by Richard Dawkins Read

Let’s talk about your first book, Richard Dawkins’s The Selfish Gene (1976). Why have you picked it? How does it fit in?

I really picked this book because for me, and I think for lots of people, it was an entry point into thinking about applying evolutionary principles to human behaviour. In a very user-friendly way, it gives you some of the basic tools you can use to start thinking about it. In my book, The Secret of Our Success, I actually say that this is a great place to start, but of course, modern evolutionary theory has gone way beyond some of these ideas.

“It lays out a particular way of thinking where you think about genes from the genes’ eye view.”

Cultural evolution—or what Dawkins described as mimetic evolution or memes—creates the second system of inheritance that feeds back and drives genetic evolution. So you have to think of these as only partially separate inheritance systems in which one can feed back and drive the other. You should also think of genetic evolution as building the machinery for acquiring culture. That’s a way in which we can use our understanding of genetic evolution to inform how we think about culture and cultural evolution.

The Selfish Gene was written in 1976. Why was it so groundbreaking at the time?

The book was synthesising a bunch of ideas that had been developed by a variety of researchers, in particular William Hamilton and Robert Trivers, on how we can think about evolutionary processes to explain things like cooperation and altruism, which has been a long-running puzzle. It lays out a particular way of thinking where you think about genes from the genes’ eye view. You think about what is good for the gene, and that allows you to solve a bunch of puzzles about altruism, about why people would help those who have copies of those same genes. But, it turned out, that was just one among a number of different ways of looking at genetic evolution.

“It’s a popular book, so it’s written to be digestible to readers who don’t have a biological background.”

Another way is to partition, to think about different groups competing and the genetic composition of those different groups, and that can be useful for certain kinds of problems. So there are at least three different ways to think about genetic evolution, which are useful for solving different kinds of evolutionary problems.

I put it on the list because it was inspirational to me, though I like to think we now have an enriched way of looking at things that goes beyond what we did in the 70s. It’s a popular book, so it’s written to be digestible to readers who don’t have a biological background. When I first read that book, I didn’t have one.

Read 2 Not by Genes Alone: How Culture Transformed Human Evolution by Peter J. Richerson & Robert Boyd Read

Your second book is called Not by Genes Alone: How Culture Transformed Human Evolution. Tell me about this book.

This fits in in an interesting way with Richard Dawkins’s book because at the same time he was writing The Selfish Gene for a popular audience, Robert Boyd and Pete Richerson, the two authors of Not by Genes Alone, had begun to hammer away at building mathematical models of cultural evolution. They were using mathematical tools from population genetics, epidemiology, and other parts of science to systematically think about how culture transmits from one generation to another — how that’s different from genetic evolution, and how it can give you different phenomena than you would get under rules of genetic transmission.

“Once you understand cultural evolution, you can explain extravagantly maladaptive behaviour that wouldn’t make any sense from a purely gene’s eye view, from the view of Dawkins in 1976.”

They’re building on work by two population-geneticists-biologists, Mark Feldman and Luca Luigi Cavalli-Sforza, who were working on similar problems beginning just before Boyd and Richerson. But it is Boyd and Richerson who ended up writing a book, in 1985, called Culture and the Evolutionary Process, which is a highly technical book, but really lays out a framework for thinking about the interaction between genes and culture — how culture can give rise to different kinds of social phenomena, how it can explain human cooperation.

Finally, Not by Genes Alone puts together 30 years of research in one place. It makes the case that culture is really important, that it is evolving, and that we can solve lots of problems—like explaining ‘the demographic transition’—by thinking about cultural evolution. The demographic transition is a big puzzle for evolutionary biology because since about 1870, Western populations have been having fewer and fewer babies. The richer you are, the more educated you are, the fewer babies you tend to have. So your fitness is lower, in an evolutionary sense. How can we explain that? One of the puzzles that Boyd and Richerson take on in Not by Genes Alone is this puzzle of why it is that Westerners, and now the rest of the world, is decreasing the number of their babies, especially among the rich. It’s an interesting way in which, once you understand cultural evolution, you can explain extravagantly maladaptive behaviour that wouldn’t make any sense from a purely gene’s eye view, from the view of Dawkins in 1976.

Going back to Dawkins and ‘memes.’ Does this mean he was open to the idea of cultural evolution back then?

Interestingly, in The Selfish Gene, he develops the idea of memes as a rhetorical tool. He is saying, ‘I’m talking about replicators and I’m trying to describe this abstract idea of a replicator. This is going to help us understand genes’ — which is really what he is trying to explain in that first book. So, as a kind of mental toy, he develops this idea that culture could be like that, that there can be memes that are passed from mind to mind, and the success of a meme depends on its ability to fertilise many different heads. So it’s interesting that it started off, for him, as a rhetorical prop, and then later, in his 1981 book The Extended Phenotype, he develops it into a fully-fledged idea.

Independent of that memes lineage, there is this lineage of cultural evolution that starts with Feldman and Cavalli-Sforza. That is a highly technical mathematical branch that then blossoms into modern gene cultural co-evolution and cultural evolution.

So what is the explanation for the demographic transition?

Debates continue, but the interesting case that Richerson and Boyd make in Not by Genes Alone is that once you have a meritocratic society in which hard work and effort and acquiring more skills, knowledge and know-how, lead you to have greater success—and part of that is going to be education—people begin putting off reproduction until later. As soon as you have women having babies later in life, you immediately reduce the total number of babies. They have a fixed window, so if you close the window a little bit, you are going to have fewer babies.

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In pre-industrial societies, children could be converted directly into economic production because they can work on the farm and they can have jobs. But as jobs demand more skill and pure labour power becomes less important, the economic value of children declines and so cultural norms of limiting family size, of having babies late, are able to spread in a way they couldn’t in earlier societies. So it is an interaction of technology, social institutions and people’s beliefs and preferences.

Read 3 Guns, Germs and Steel by Jared Diamond Read

Book number 3 was a big bestseller, this is Guns, Germs and Steel by Jared Diamond. Tell me about that and why you’ve picked it. So this is a book looking at 13,000 years of history?

I read this book as I was going into my last year of graduate school at UCLA. I had just returned from doing fieldwork in a remote part of the Peruvian Amazon, where I was studying the indigenous population called the Matsigenka. They were always asking me questions—lots of questions that I thought were really complex and pretty deep—and one of the questions they asked me was, ‘You anthropologists come here and study us, but we never get to go to where you are from and see how you guys live. Why is it that you seem to be so rich and have so much and we have so little?’

“Oftentimes populations need an invention and they never get it, and instead they die out.”

I found that a difficult question to give an easy answer to. Then, when I came back, Guns, Germs and Steel had just come out and a friend gave it to me as a gift. The first chapter is about a conversation he has with a guy in New Guinea, in which he gets asked, basically, the same question as I had been. Guns, Germs and Steel is his effort to answer that question. He calls it ‘Yali’s question’ in the first chapter.

The book is a masterpiece in terms of integrating a vast range of material from different disciplines, material on language, archaeology, comparative bio-geography, with also lots of his own ethnographic field studies peppered in there. It was inspirational to me for doing that kind of work. The Secret of Our Success, the book I wrote, has that flavour of pulling together stuff from across the diverse social sciences. It is not an effort to readdress the question that Jared Diamond answered in Guns Germs and Steel, but it’s very much an inspirational book in terms of the size of the questions one can ask and the scope of one’s research — if you are willing to rely on other people and don’t feel the need to be an absolute expert on everything you say.

Are there helpful insights in there for the work you do?

One thing that fed into my later work is the chapter in Guns Germs and Steel called “Necessity’s Mother.” In that chapter he makes the case that necessity is not the mother of invention, that it’s much more of a social process. Oftentimes populations need an invention and they never get it, and instead they die out. He goes on to talk about that more in a book he wrote later called Collapse. There are lots of urgent things that societies need that you think they might invent but don’t. Then oftentimes when inventions do pop up, they drift around for years and nobody puts them to use until finally somebody figures out how to use them.

That got me thinking about innovation that then influenced my work on the collective brain. The idea of what generates innovation is actually the free flow of ideas, information, and practices among diverse minds. That means that the size and inter-connectedness of societies affects the rate of innovation. It turns out, when you model it, it’s the most important thing. For example, it is much more important than being smart.

Is Guns, Germs and Steel well regarded? Do the people accept the thesis that he puts forward or are there lots of people saying it’s completely wrong?

The first thing I would say is that, whether you think it is right or wrong, it’s spurred an incredible amount of research. People took it seriously and fully engaged with it. It’s driven economists to get better data to test the theory. So, for example, there’s a number of economic studies now supporting Diamond’s basic thesis. Researchers went and got the date for the earliest beginning of agriculture in different parts of the world, and then used that to predict modern economic development — GDP per capita in the year 2000. You control for a lot of factors statistically, and it is still seems to be the case that what Jared Diamond presented very qualitatively—that the earliness of agriculture really matters—does hold when you do statistical analyses.

My own work and the work of others supports the ‘necessity’s mother’ parts of his work.

And certainly, more studies on disease and pathogens have continued to support that part of his argument, where he argues that people in the New World and in other parts of the world had a great susceptibility to the pathogens that Europeans brought with them. The differences in domesticated animals in different continents, say, caused pathogens to spread and destroy many populations.

I would say the most controversial part of his work—the place where there is the strongest disagreement—is about what’s happened in Europe since 1500. Diamond tried to make the case that you can go all the way back to the origins of agriculture around the world and use that to explain the poverty and wealth of nations in the year 2000. What the current evidence supports is that you can predict the poverty and wealth of nations in 1500 really well with what Jared Diamond found. Then, what happens in 1500 in Europe, seems to require additional explanation: something else was afoot in Europe after 1500 that eventually lead to the Industrial Revolution and the mass of European expansion after that.

So I would say, he is doing pretty well on the terms of the evidence that’s come in subsequently. Mostly support has increased for his thesis, except for the since-1500 part of economic growth.

Read 4 The Creation of Inequality: How Our Prehistoric Ancestors Set the Stage for Monarchy, Slavery, and Empire by Joyce Marcus & Kent Flannery Read

Let’s go on to the fourth book, The Creation of Inequality, which is by two anthropological archaeologists.

This book is all about how societies scaled up and stratification developed. If we go back before 10-12,000 years ago, current evidence suggests that most societies were relatively egalitarian; they didn’t have different social classes. What Flannery and Marcus do very systematically is document different ways in which societies have scaled up and become more complex, and added inequality by having social stratification. The beautiful part for me is the way they integrate ethnography. They go back and pull together many different ethnographic sources on different societies around the world, societies that we know a lot about because a lot of anthropologists have been there and recorded the details of how the society functions. Then they put that together and use it to enrich archaeological cases, whether from Mesoamerica—Mayan, Aztecs, Inca societies—or Mesopotamia and other places.

“What we are seeing is a process that’s repeated itself many, many times over, where gradually, over a long period of time, the elites change the rules of the game so they are increasingly favoured. There are various ways to get out of the trap. The usual one is revolution, collapse and discord, but hopefully there are other ways out too.”

The problem with archaeology is that you just have the material remains of past societies. It is hard to make inferences about the religion or social structure from the buildings that were left over, the tools people used, or the foods people ate. But Flannery and Marcus show, in my view persuasively, that you can use ethnographic cases to enrich your understanding of the archaeological record, and then look at how things like religion, the organisation of clans, and a bunch of different social factors allow some societies to scale up and get stratification, whereas other societies seem impeded by their social structure from scaling up. They don’t end up being larger and more integrated, but they also don’t end up with high degrees of social inequality.

I’m quite intrigued, so in that time-scale, going that far back, you can have convincing evidence about how a society was structured?

What you do is you map the things you can see in the material record. So you have burials, for example. How are people buried? What are they buried with? What are their children buried with? If a society is achievement-based, then the kids haven’t achieved anything, and the kids are buried without any trappings. But in societies where you have hereditary power, in which one group of people are better by virtue of their birth than other people, then the kids often get buried with lots of fancy stuff. That’s one of the markers you can use, and you can see that that is persistently the case in societies where we know the details from ethnographically-known societies.

Then, when we look back in the archaeological record, sometimes you see societies that have big monumental architecture. That might make you think, ‘Oh! social stratification, they must have had hereditary chiefs.’ But then you see that the kids aren’t buried in a fancy way. Then you can begin to look at other parts of the economy — distribution of house sizes, say, or the kinds of crops planted, trade.

With growing inequality around the world today, does reading this book help shed any light onto current problems?

It points to something that is recurrent in the work of many researchers — also like Peter Turchin, the ecologist-turned-historian. When societies are competing, this high competition tends to keep inequality down. Then, over time, the elite of a society—consciously or unconsciously—gradually twist the institutions and change the social norms so they get a disproportionate share of the pie.

What we are seeing is a process that’s repeated itself many, many times over, where gradually, over a long period of time, the elites change the rules of the game so they are increasingly favoured. There are various ways to get out of the trap. The usual one is revolution, collapse and discord, but hopefully there are other ways out too.

Read 5 The Cultural Origins of Human Cognition by Michael Tomasello Read

Your last choice is The Cultural Origins of Human Cognition (1999) by Michael Tomasello.

This is one of the earlier attempts to consider cultural and genetic evolution. He is interested in something he calls the ‘ratchet’ effect. This is something we only see in humans. Humans can produce novel ideas, behaviours, and practices, and our cultural learning is sufficiently high fidelity, that the next generation can get those ideas and practices and bodies of knowledge and build on it incrementally, so that, over generations, you have this accumulation of cultural know-how. Now other animals can learn from each other, but the loss of information between generations is sufficiently high that they never get anywhere. They never get this accumulation of more and more know-how over generations — at least as far as we know, and, if they do, it is pretty light.

“Lots of subsequent work has borne Mike out on that the key element in getting cumulative cultural evolution, which is high fidelity cultural transmission. You get faster and fancier tools the higher fidelity the transmission.”

So Mike is interested in how we got that because there’s a question in human evolution of how our brains got so big so quickly. It would seem to demand what researchers call an ‘autocatalytic process’ — the process had to fuel itself. It had to get stronger and stronger. Gene cultural co-evolution can provide that. So if you have a little bit of cumulative cultural evolution: you get some fancier tools and a larger body of knowledge, then there is greater selection pressure for bigger brains that are better at acquiring, storing, and organising that information. Then, once you have brains that are better at doing that, you’ll get more cultural information. So the body of know-how will become larger. Then you need an even bigger brain that’s even better at that stuff.

Mike looks at this ratchet process and he argues that the key adaptation was what he calls ‘theory of mind’ or ‘mentalizing’. The fact that humans are particularly good at inferring what other members of their social group are thinking allows them to be better social learners, and that gives them the high fidelity transmission of knowledge across generations which gives you the ratchet effect.

He makes the case that there’s one big genetic adaptation, theory of mind, and that that then generates the ratchet process. He also argues that language is a product of the ratchet process, that you get fancier languages and grammars over time.

What’s his evidence for this argument?

He’s a comparative developmental psychologist, so a lot of his evidence comes from comparing humans and chimpanzees or other primates and apes, and at the way children accrete knowledge when they are learning a language. You can compare that with communication systems in another species. Those are his main data sources. He looks at the ways culture accumulates over time.

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Lots of subsequent work has borne Mike out on that the key element in getting cumulative cultural evolution, which is high fidelity cultural transmission. You get faster and fancier tools the higher fidelity the transmission. There’s lots of ways to increase fidelity—people or animals can get better at learning from others—but they can also become more social and hang around each other more. You can also have the evolution of teaching, where the transmitter actively helps out the learner and helps make sure they pass on the knowledge. Teaching seems to be something that’s particularly important for human cultural transmission, although there’s lots of cultural variation in that.

The books also got me thinking about language. I assumed that a lot of language learning was innate, or that we had lots of pre-built, evolved machinery for it. In my book, The Secret of Our Success, I make the case that languages, actually have, even in historical time, gotten more complex, added new tenses, added new grammatical tools, vastly increased the repertoire of vocabularies, gotten more phonemes, and all kinds of things that go along with the rise of complexity. So languages are really just like other domains of culture—like tools—in that they are cumulative and depend on the size and inter-connectedness of populations.

Has Mike’s work been generally accepted? Is it seen as a textbook to follow, or is it more controversial?

It’s been hugely influential. It’s created whole research programmes and driven lots of research. I part ways a little bit with Mike here and there on what it takes to get the high fidelity cultural transmission. In the case of humans, I argue that it wasn’t some magic genetic bullet that allowed humans to get cumulative cultural evolution, but that we’re a primate and that we had, maybe, chimpanzee-like social learning, but that we lived in a different social structure, and it was actually differences in social structure which allowed humans to begin this cumulative accumulation of knowledge. It was a change to greater sociality. So there was no difference in learning ability, but more people to learn from, more sociability and more tolerance allowed humans to cross the divide and begin down this road of gene cultural co-evolution.

Various ideas of Mike’s have become widespread. Some have been disagreed with, but in terms of the general importance of the ratchet effect, and cumulative cultural evolution, that seems quite mainstream at this point.

It seems that if humans do depend so much on sociability and interaction, I expect great things to happen from the internet — and the huge and constant interaction of people and information that it allows.

Yes, it is a good test of the ‘collective brain’ idea. If the collective brain idea is right, when we look back historically on this period, the early 21st century, we should see a massive increase in rates of innovation because of all the interaction the new communication technology is permitting.