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Joe Henrich: Cultural Evolution and Dual Inheritance


(soft piano) – [Narrator] We are the paradoxical ape. Bipedal. Naked. Large brained. Long the master of fire,
tools, and language, but still trying to understand ourselves. Aware that death is inevitable, yet filled with optimism. We grow up slowly, we hand down knowledge, we empathize and deceive. We shape the future from our shared understanding of the past. Carta brings together experts from diverse disciplines, to exchange insights on who we are, and how we got here. An exploration made possible by the generosity of humans like you. (upbeat music) – Our next speaker is Joe Henrich, who unfortunately couldn’t join us. I’m happy to say that he
was able to record his talk, it’s a very important talk on
a second mode of inheritance that doesn’t involve DNA, but culture, and it interacts with the
first mode of inheritance. So he is Joe Henrich,
from Harvard University, on Cultural Evolution. – [Joe Henrich] Hi everyone. I’m Joe Henrich. I’m sorry I couldn’t be with you today, but in the next 14
minutes I’ll be giving you an introduction to recent developments in our understanding of cultural evolution and dual inheritance theory. With an eye to how this informs our understanding of human evolution. Our point of entry for
understanding cultural evolution and our species dual inheritance, is to recognize that humans
are a cultural species. More than any other species, we’re dependent for our very survival on acquiring this large body of information that is accumulated
non-genetically over generations. We use this to find food, to process it, to make tools necessary
for getting the food, for building shelters, for medicines, for even features of childbirth that other species do automatically humans need specialized
cultural information. So, culture is central
to understanding humans, and we can’t survive without it. Despite having these large
brains that have evolved, surviving as hunter-gatherers for so long. Now to approach this,
we need to think about our adaptations for our cultural learning as genetically evolved adaptations. Natural selection has
shaped our minds to make us better cultural learners. This, I think, is a crucial intellectual move in history, these ideas. Because making this move dissolves the intellectually destructive dichotomy between genes and culture. And it allows us to make
all cultural evolution a type of evolutionary explanation. To insert them under
the Darwinian umbrella, and to use the full power
of evolutionary theory to think about our cultural capacities as genetic adaptations. Now the way to build an understanding of cultural evolution and dual inheritance is to begin by asking the question “how might natural selection
have shaped our cognition to best exploit the socially
available information that’s in the minds and behaviors of the other members of our social group? How do we filter that wash
of social information?” And there’s a large body
of formal evolutionary mathematical theory that asks the question when should we rely on
pre-programmed responses in a decision making heuristics, individual learning and experience, or cultural learning or
learning from others. And to give you a sense of
how we think about this, you can imagine you’re
entering a novel environment. Perhaps you’re a young individual just growing up in a group, learning to make your way in the world. Perhaps you’re a migrant
from a different environment, and you have to solve a basic task. How do you figure out what
to eat in this environment? Now you might use individual
innate learning cues, sampling a lot of foods trying
to figure out what to eat. This would allow you to
construct a good diet over time, but it would be costly
because you’d have to sample all these foods, you’d have to have some
good detoxifying processes, you might make yourself a
little bit sick sometimes, so that’s potentially costly. The cultural learning
solution to this problem is to eat what other people eat. And you can even sharpen that up a bit, by focusing on the food choices of older, healthier, and
more successful people. You don’t know that this will give you the best possible diet
in this environment, but you do know that it will give you a diet that can allow you to become older, healthier, and successful. Now researchers in approaching
this have identified a number of different
classes of mechanism. I’ll mention two of them. The first is model based mechanisms, and that’s rooted on who
you’re trying to learn from. So that’s relevant to the
last thing I said about older, healthier, and
more successful people and learning to eat from them. So that’s about the who. I’ll say more about that in a minute. The other one are
content based mechanisms. So, selection seems to have favored some inclination to pay
attention to certain domains. So people are particularly
interested in food, you know that from all the cooking shows. Fire, there seems to be a
period during middle childhood where children become
particularly interested in fire. Artifacts, we seem to
approach them in certain ways, and make certain
assumptions about what one needs to know about artifacts. Social norms, where we
kind of learn social rules, I’ll say more about that in a few minutes. We focus on social groups
and we try to learn things about whole categories of people. And living kinds, we seem to
have some specialized cognition for dividing up the natural world. And in fact, we focus on
certain kinds of information. So children readily acquire and remember information about the
dangerousness of different species. To give you a sense of how
researchers have approached this, let me talk about model based
selective cultural learning. So here the idea is to build
a theory to allow us to investigate the kind of cues learners use to figure out who in
their social environment to pay attention to. Some obvious ones are, pay attention to the more
skilled or competent individual. So if you’re in a hunting
and gathering band, you want to look at the best archer if you want to become
a good hunter some day, or the person who makes the best snares. A way of aggregating this is to look at the most successful people. So who brings back the
most prey consistently? A way to get to that quickly, could be to use prestige cues. So rather than aggregating who brings back the most prey most frequently, you can look at who other
people pay attention to. Who do they imitate? Who do they defer to in
conversation about hunting? So these are skill, success,
and prestige biases. All of which have been
shown not only in adults, but in young children, and in some ways things like
reliability and competence have been shown in babies. Young children there’s good
evidence of prestige bias. Other cues could be something like age, which allows you to
very quickly zoom in on individuals likely to
have useful information by using age as a proxy. Younger children copy older children, and only certain people get to be old, especially in small scale
societies that can be a cue. Self-similarity cues can help
individuals zero in on those most likely to have information useful to your future roles in life. Research on social learning has shown that these cues in general, not each one, are operative across a
wide range of domains. So people use social learning
to acquire food preferences, to pick mates, to determine which technologies
they’re going to adopt, economic strategy, suicide. Reputational information
is transmitted culturally, and what goes into a
reputation in particular. Social motivations like
fairness and punishment, are also well established to
be culturally transmitted. These biases and inclinations
reliably develop. We have cross cultural evidence, including some from small scale societies, although we could use a lot more of detailed experimental evidence. But they develop early, they’re automatic, and they’re often unconscious. So this has the look of
a cognitive adaptation. The next step in this process is to think about cultural evolution. So we’ve used the logic
of natural selection to get us an understanding of the psychological mechanisms which allow us to acquire cultural learning. So next you can build mathematical models which describe social processes of interaction between people, some learning and some payoffs, some social interaction. That help us explain aspects of religion, help us explain why
some aspects of religion seem to be universally shared, and why we have this historical
trajectory of beliefs and say big moralizing gods or these large doctrinal rituals, it can help us understand
why technologies can become so sophisticated, and why larger and more
integrated societies tend to produce faster adaptive rates of cumulative cultural
evolution leading to fancier technologies and
larger technical repertoires. It can explain why
languages are so variable. Similarly large societies
have more words for example, particular kinds of grammatical systems. On the next slide I’ll discuss social norms and cooperation a bit more, and this approach can
help us understand why ethnic groups seem to be
so widespread in the world, and what’s the nature of
our ethnic psychology. Which brings us to the large pink arrow, which is reminding us that
these cultural products having operated over tens, or even hundreds of thousands
of years of human evolution have fed back to shape
our genetic evolution. So we’re a product of this
gene culture coevolution. From this broad range of
topics on cultural evolution, I’ve picked out just one. The evolution of cooperation, or what Pete Richardson
calls human ultra-sociality. Now there’s been a great deal of work on human cooperation showing the role of kinship and reciprocity. But in addition to this, efforts to understand
large scale cooperation have shown the centrality of social norms. And subsequent investigations to better understand kinship and reciprocity has shown that even in that domain, or even where those
mechanisms are involved, social norms are crucial. There’s now a large body
of psychological work showing that based on humans
from diverse societies that humans culturally learn norms, social norms seem to be a universal. When humans acquire norms, they acquire and internalize motivations, they automatically infer
expectations of punishment or some kind of sanctioning
based on reputations, and they acquire standards
for judging others. All by simple observation. So it seems that humans have some kind of norm psychology. Social norms are stable,
because anybody who acts faces a threat of punishment by others, and so that keeps the whole group in line. This is why things like
economic development, other kinds of social change, are so hard. One of the interesting
and emerging areas is what are the different
mechanisms that maintain norms across societies? It had been assumed that
the debate was about one kind of mechanism, but it turns out that cultural evolution has figured out lots of ways
to maintain social norms. So these vary both across societies, and even in different
domains within the society. One of the important areas moving forward, is considering how the
emergence of social norms through cultural evolution has shaped our species genetic
evolution, and our sociality. So one idea is that the
threat of reputational damage and other kinds of costly
punishment to norm violators has initiated a process
of self-domestication. This suggests that there’s a syndrome that we share with other
species like domesticated dogs whereby selection favors certain genes and their downstream hormonal
and psychological effects they created a domestication-like effect. We have many of these,
but not all of these when you compare us with other species. One of the key elements is
what Richard Wrangham calls reduced reactive aggression. A kind of general docility. This would also favor the
kind of norm psychology I discussed on the previous slide, this readiness to acquire
and internalize social rules. It may even lead to pro-social biases. These biases that we get to
acquiring pro-social norms which would have resulted because of the effects of inter-group competition favoring more group beneficial norms. Complex tools and technologies over time. So that’s the crossing of the Rubicon, you get some cultural evolution going. Culture begins to become
a semi-independent inheritance system
alongside genetic evolution. Early cultural evolution may
have produced things like stone tools for cutting
and processing food, fire and cooking may have created a kind of externalized digestion, which weaken the selection pressures, allowing our stomachs to shrink, changing other aspects of our physiology. This would have freed up more
energy to build larger brains, giving us larger dexterity for
using tools and making tools. This then would’ve created
a greater selection pressure for brains able to
acquire, organize, store, and re-transmit cultural information, because that’s the name of the game. Cultural evolution then
could have produced more knowledge about throwing techniques, about how to find tubers, about how to make water containers. Water containers would
have opened the door for long distance running, which would have created
genetic selection pressures for springy arches or long legs. Eventually we might’ve
gotten shortened colons, having to do with the fire
and cooking I mentioned, and even larger brains. Because now, there’s this growing body of valuable behavioral information
that’s only available if you’re a good cultural learner. And you’ve got to acquire and store it, and eventually re-transmit it. You get cold weather clothing, better tools allow us to have thinner bones and weaker muscles because we’re relying more on technology. Things like resins and other
kinds of projectiles can emerge and then eventually a
cognition that allows us to acquire and store all this knowledge. About different kinds
of plants and animals, because we’re now in the cognitive niche, or the cultural niche, and minds that are better able to acquire information about artifacts. And eventually this can
effect human life history, giving us an extended juvenile period, a longer post-reproductive period, because as you extend life, older individuals have an opportunity to re-transmit back to younger generations this large body of information they’ve accumulated over time. All right, that’s it. If you wanted to learn more
about some of the ideas I presented here, you can
have a look at my book The Secret of Our Success. (audience clapping) (upbeat music)

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