How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter

How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter


And it’s a real
pleasure to be here to introduce my
colleague Joe Henrich. Joe studied at
Notre Dame and UCLA where he earned degrees in
both anthropology and aerospace engineering– just an
interesting combination. And he taught at Emory and the
University of British Columbia. And he’s the only person
on the planet, I believe, who– I could be wrong, but
I’m pretty sure that this is a safe statement– he’s
the only person on the planet has been granted tenure in the
following four disciplines– anthropology,
psychology, economics, and human evolutionary biology. But despite this array
of accomplishments, we managed to recently
woo him to Harvard, and I’m really
pleased that he’s now a professor in the Department
of Human Evolutionary Biology. And we really couldn’t be
more thrilled to have him here because, if alien biologists
ever landed on this planet, and they were asked to
describe various creatures, including us, you can be
sure that the feature they’d probably single out as most
distinctive about human beings is our capacity and proclivity
to use culture in almost every context imaginable. And maybe our second most
distinctive characteristic is our proclivity to
cooperate as we’re all doing here making seats
for each other in the room. It therefore follows that if you
ever– if we ever really want to understand why humans
are the way we are, and we need to understand,
therefore, how culture evolves, how and when we
cooperate, and how cultural evolution interacts
with biological evolution, which made all this possible. And that’s what Joe studies, and
that’s why we’re here tonight, to hear him. Because he’s probably
the foremost scholar in the world who studies
the evolution of cooperation and the capacity for
culture in humans. He does this using
several major approaches. First, he conducts really
ingenious, and creative, and innovative cognitive
and behavioral experiments in many different
cultures across the globe. Second, he’s a very
sophisticated theoretician who has developed a lot of
important new mathematical techniques for analyzing
cultural evolution. And finally, he goes
out into the field and collects empirical data
from small scale societies in many places,
including– most of them seem really warm and
pleasant, like the Amazon, rural Chile in the South
Pacific– South Pacific sounds particularly
nice at the moment– and he uses this using a
variety of ingenious techniques from psychology, and cultural
anthropology, and economics. He’s published
hundreds of papers, but the most cited, by far, is
his very famous Weird Paper, in which he points out that
most research subjects that are used in studies of
behavior are highly biased. They’re Western-educated,
industrialized-rich, and democratic– weird. And although these adjectives
characterize all of us in this room, I hope you’ll
agree that we are definitely not very representative
of our species as a whole. And so by now you
know that he recently published a book on these
topics, The Secret Of Our Success: How Culture Is
Driving Human Evolution, Domesticating Our Species,
And Making Us Smarter. The latter part
sounds very important. And by the way, having
read it, I can promise you it’s a really
entertaining, delightful, and thought-provoking book. I particularly
recommend chapter 5. So, I hope you
enjoy the lecture, and without further ado,
it’s a real pleasure to welcome Joe Henrich. Thanks. Thanks Dan. And hi everyone. Thanks for making it
out on this wet evening. So I want to begin by talking
about the ecological success of our species. And of course, in
the modern world, it’s obvious that we’re highly
ecologically successful. So 98% of the terrestrial
vertebrate biomass consists of humans and
our domesticated animals. But the puzzle of our species’
immense ecological success extends well back into our
species evolutionary history. So long before the
origins of agriculture, or the first cities, or
industrial technology, humans are expanding
out of Africa. So our species emerges in
Africa and expands out– so 100,000 years ago
or a little bit. More recently, we
expand out of Africa, 70,000 years ago into the
southern part of Asia. And then, sometime
after 60,000 years ago, we arrived in Australia, after
50,000 years ago into Europe, and then into the Arctic some
time after 40,000 years ago, and then eventually
into the New World, all the way down to the
tip of Tierra Del Fuego, before the origins
of agriculture. And as we spread into
those environments, we ended– or we entered
an immense diversity of environments. So from the arid
deserts of Australia to the malarial swamps of New
Guinea, up into the Arctic tundra in Siberia,
and eventually Canada, mountains in Tibet, and
then an immense diversity of environments
in the New World. And what’s interesting
about our species is we go into all
these environments, but we have very few
genetic adaptations to these in diverse
environments. And this important in
thinking about our success because when we look
at other species that have been very ecological–
ecologically successful– so if we look at ants,
we find that ants, they control a lot
of biomass, they go into a lot of
different environments, but they have an immense number
of environment-specific genetic adaptations. In fact, they’ve speciated into
over 14,000 different species. But we’re a relatively
genetically homogeneous species, yet we inhabit
this immense diversity of environments. So the question is,
how did we do it? Now, for probably for many
of you this wasn’t– you hadn’t thought much about
this being a problem because there’s
an obvious answer. The common sense answer
is we’re intelligent. We have big brains, lots
of mental firepower, and we can just figure
out how to solve problems. And it’s this ability
to build causal models on the fly that
allows us to enter all these different environments. And I want to start
this talk by trying to challenge this
idea that it’s just our intelligence, our raw brain
power that gives us our ability to enter diverse environments. So I want to begin by dipping
into the lost European explorer files. Now this is a set of
files that Rob Boyd and I have been putting together. And there are cases where
lost European explorers, or sometimes Americans,
end up stranded while exploring in
some environment that’s inhabited by hunter gatherers. And so the explorers
then need to survive. They need to find
food and water. They need to know how to
travel and make tools. And I like cases where–
well, there always has to be a group
of hunter gatherers that’s been surviving
there, preferably for centuries or millennia
is usually the case. And they need– I like them to
have lots of food and security at the beginning. So I don’t want them in
an emergency situation. They need lots of time to
warm up to the environment. And then what be find in case
after case is they flounder. They can survive as
hunter gatherers. So this is the story
of Burke and Wills. So it’s 1860, and
they’re endeavoring to be the first Europeans
to head across the center part of Australia. It’s a very interesting story. I’m going to cut it kind of
short, get to the punchline. They make it up to the
Gulf of Carpentaria, and they’re heading
back, and things are starting to
go wrong, and they decide to make a last ditch run
for a police and ranch that’s prophetically called
Mount Hopeless. So they begin heading
along Cooper’s Creek, and their last camel– they’d
imported camels from India for the expedition. The last camel dies. It gets stuck in
the mud and dies. And this means they
can’t get the water they need because they needed
the camel to carry the water to get across the last
stretch of desert, to get to the ranch
and police outpost. So they’re essentially
marooned along Cooper’s Creek, and they’re hoping
a rescue party is going to come from Melbourne. So they try fishing
and hunting, and they can’t get enough calories
from fishing and hunting to stay alive. They occasionally
get stuff, they have guns but they’re
running out of bullets and things are going wrong. But things start to look up
when they meet the Yantruwanta So those are the local
hunter gatherers who have lived in this
environment for a long time, and they’re able to get gifts
of fish from the locals. And they see the locals
making cakes and gruel from a small sporocarp. And they manage to track down
the sporocarp after quite a bit of wandering around. They initially thought
it would be in a tree, and it turned out
to be on the ground. And they know how to bake bread,
so they grind up the sporocarp. And it looks like they’re
going to get enough calories because they’re getting the
occasional gifts of fish, and they’re able to make
lots of gruel and cakes from these things. The problem is when they
were in the aboriginal camps, they didn’t notice that this
is processed by the women by two possible methods. One is to grind it, leach
it, heat it, and then use it with a mussel shell to eat it. Or grind it, leach it,
and then bake it in ash. And either of these methods
has an important effect on the nardoo because nardoo
is toxic and indigestible unless properly processed. You’ve got to remove this
enzyme called Thiaminase, otherwise it depletes the
thiamine in your body, the B1, and you get a horrible
disease called Beri Beri, and eventually you die. And this is what happened
to Burke and Wills. Now there was a third
member of their party still alive at this
point named King. King, he’s having the
same kinds of symptoms, and we know this in part
because William Wills is– he’s a good Victorian right? So he’s writing in
his diary as he’s dying describing the
experience and everything. You can read it online it’s
actually interesting reading. So King wanders out
into the desert, and he’s eventually picked
up by the Yantruwantu and eventually
rescued by a search party that came from Melbourne. So we know the story
from King’s account and also from
William Wills’ diary. So what this and
many, many tales like it tell us is
that Burke and Wills, they had three with three months
of food with them initially. They couldn’t survive as
hunter gathers in a place where humans have been
surviving for over 60,000 years. So no modules fired
up that allowed them to find edible
plants and make fire. No instincts kicked in. No general intelligence
bailed them out. So they couldn’t do basic things
like find water or identify edible plants, but they were
able to find deadly plants. Now you might think that
that’s kind of a lot to ask to be able
to do these things, but we have a little bit
of a controlled experiment because I mentioned
those camels. Well some of those camels had
escaped from Burke and Wills earlier in their
adventure, and there’s now thousands and thousands
of feral camels all over central Australia. So the camels survived the
lost European explorer. Camels can smell water
from a mile away, and they have taste cues
which allows him to find certain kinds of plants. They’re really good
a detoxifying plants when they eat it. And they actually
have taste cues that help them find plants
that are high in protein. So they’ve got lots
of great adaptations that Burke and Wills
and other humans lack. So the camels beat the test. And their brain is
less than half the size of the Homo Sapiens. So these guys, they
couldn’t hunt effectively or make any of the tools. And one example of the
knowledge they lacked was this plant called spiniflex. If properly processed,
spiniflex makes a powerful cement-like adhesive. But you have to know that you
have to harvest these grains from this kind of– doesn’t
look like a great plant to me– and put them in
fire and actually mix kangaroo dung in with them
to get them to really work like a good cement, very
non-intuitive aspects of the process. So they can’t do that. But any local adolescent
could have done these things. So you can ask
yourself, well what were Burke, and Wills,
and King missing that these local
adolescents would have? Well the answer is
obvious, that they were missing this large
body of inherited know-how that teaches you about
processing nardoo and teachers you about spiniflex and
helps you find water in the desert, where
otherwise this would be very difficult to find. So this body of
cultural knowledge seems to be key to
understanding humans in a way that it’s not for
understanding camels. OK. Now I want to come at this
from another direction, which is to look at some work done
by Mike Tomasello and Esther Hermann and their colleagues
at the Max Planck Institute for Evolutionary
Anthropology in Leipzig. So what these
researchers did is they created a contest between three
different apes, so orangutans, chimpanzees, and then humans. The humans in this case
are 2 and 1/2 year olds, so I substituted a picture
of my son Josh who happens to be 2 and 1/2 years old. And they gave me a battery
of cognitive tests, 18 different cognitive
tests in different areas. So you can break the
test down into tests about space, quantities,
causality, and social learning. So there’s a bunch of
subtests in each of these. And this is the percent correct. And each of these species is
very interested in snacks. So if you get the test
right, you get a snack. So there’s incentives
for performance. And so you can see the humans
and the chimps, the 2 and 1/2 year olds and the chimps, do
about the same in the space test, the orang’s
a little worse. Chimps slightly beating them–
although within the margin of error for sure. In the quantities
test, causality test, slight victory to the chimps,
margin of error though, and the orangutans seem to
lose by a little bit each time. But the place where
the kids clean up is in the social learning test. So, in this case, the
kids are up in the 80s and the apes– or
the non-human apes– are all down here below 10%. So this is a big difference. In fact, this is
actually deceptive because, when you talk to
Esther Herman, the lead author on the study, it
took her a while to find a test
where she could get the apes off the floor from
0% and get the kids away from the ceiling, get
them down from 100%, because kids are such
good social learners. OK. Now you might think, well this
is kind of unfair to the humans because you’re using
2 and 1/2 year olds and these apes are
all different ages. So there are some
infant apes– so less than five years
old– and then older apes. And that might seem unfair. But what’s interesting
is the apes don’t get better with age
on these cognitive tests. In fact, in some of
the cognitive measures, the infants– the
five-year-olds, four-year-olds– actually do
better than the older apes. But in the case of
Josh and his cohort, they’re going to
continue to get better and better at these tests
into the third decade of life at least. And by the time they
get to be in their 20s, they would ceiling
on all these tests. They get 100% on all
the things, and so they would crush the apes. So something is going on
over these few decades. And I’m going to be telling
you about that in a second, or at least part of
what I think that is. I wanted to mention,
though, in the book, I also discuss
interesting research which compares undergraduates
in terms of their working memory abilities, which
is often thought to be a center piece of IQ
and intelligence, the working memory, in which
the chimps do quite well in comparison to the
humans, the undergraduates, in working memory. And in measures of strategic
thinking recently done by some Cal Tech
economists, in collaboration with some Japanese
primatologists, the apes outperform the humans. They’re able to
zoom in on the Nash equilibrium, the optimal
behavior, in a way that the humans
systematically miss it. So they’re better
Machiavellians than humans. OK. Now why are we so smart? That’s an obvious question. We know we’re smarter
than these apes. We’re better at
solving problems. Why? Well part of the reason
is that we culturally inherit lots of
pre-built solutions that have culturally evolved
over long periods of time. So, some examples is if you
think about simple tools like things like screws,
springs, levers, and pulleys, these things turn out
to be hard to invent, and I’ll give you some
examples in a minute. But if you grew up in a world
where these tools already exist, you get to see
them in operation, you get to learn
their affordances, and you can redeploy them
to solve new problems. But hard to figure out
if you never get never get to see them before. My favorite example
of these is the wheel. So if you learn your
technological histories from the far side,
you might think that the wheel goes well back
into the human paleolithic, and that paleolithic peoples
were using the wheel. But wheel’s actually relatively
late in human history, so about 6,000 years ago. You get a potter’s wheel. You get wheels on carts like
this, wheels for milling grain. But that only
appears in Eurasia. So in the New World,
no wheels except on Mayan toys– no
wheels in Oceania, no wheels in New Guinea,
no wheels in Australia, no wheels in Africa. So something as
simple as a wheel doesn’t appear in
these other places. Then once you have
the wheel, you can do all this
different stuff with it. Sometimes there is that– I
put this picture of the dog up there. This is in Belgium. There’s this idea that there
is no domesticatable animals to use the wheel, but
everybody had dogs, and the Belgians hooked
their wheels up to dogs. Also elastically-stored energy. So in Australia, you
don’t get any tools with elastically-stored
energy or compressed air. So that’s a whole
continent which doesn’t get these concepts. Number systems. So all of you, I think I can
say with great confidence, have inherited a
number system that allows you to count
without bound, neatly packaged
into groups of 10. You can perform all kinds
of cool operations with it. But anthropologically-known
societies, like the group I worked with in
Peru, the Machiguenga, just count one,
two, three, many. So they don’t have a way
to digitally distinguish between 16 and 17, or 34 and 35. And then when you study
comparative number systems studied by anthropologists,
you find not every combination, but almost any combination,
some groups count to 11, some groups count to 12. It’s often a kind of body
part counting system. So you can see this
group counts to 27, but then there’s no way to do
31 and 32 with this system. And so the gradual evolution
of numbering systems over time, we get this free of charge. Another interesting one
is spatial cognition. So, as a consequence
of speaking English, you all have access to three
different spatial coordinate systems. So the first is absolute, so
North, South, East, and West. The second is an object center. So you have a front,
and a back, and a side. Your house has a front,
and a back, and a side. You can say, I’ll meet
you in back of the house. I’ll meet you in
front of the house. Those things are
readily distinguishable. And then there’s a
relative coordinate system. I could say, it’s the guy
to the right of the camera, and that draws a line
between me and the camera and goes to the right
if it or to the left. It’s a relative
coordinate system. But other groups studied by
anthropologists just have one. They just have North,
South, East, and West. So you’d always have
to say it’s the guy to the North of the camera
or the South of the camera. There’s no relative
coordinate system to use. And you can imagine something
like driving on the left or driving on the right, it
has a certain kind of usage that allows you to solve
new kinds of problems, where otherwise
you’d have to say for every street you have to
memorize North versus South or something like that. So it’d be awkward
in some cases. So that’s something
that’s evolved over cultural evolutionary time. OK. And one of the
things in the book is you can read about lots
and lots of these examples. So the case that I
make is that it’s not our intelligence, meaning
or raw, individual ability to solve problems that leads
to our species immense success, but our cultural
capacities, that accumulated body of know-how the Burke
and Wills didn’t have. And the fact that we can
learn from each other and we can pass this down
over generations, in just a particular way
that I’ll talk about, gives rise to these
cultural adaptations. So these are pre-built
solutions to problems that we face in the environment. So a couple of keys
to this, one is that in order to get
this going– well it works best if your
high-fidelity cultural learner, so you can observe other
members, your social group, and infer underlying goals
and mental states and action patterns. You can get it
going a little bit if you’re less good at that,
but the better cop you are, the better that goes. And also you have to be social. So the more
interconnected you are, the better the system can run. Now you might– some
people try to say, well, this is actually a
measure of intelligence. But when we– anytime we try to,
sort of in a common sense way, measure intelligence,
one of the things is we say is you can’t copy off
the other guy’s paper, which seems to be the kind
of gut reaction. You don’t have to do
that with capuchins, for example, if you want
to test their intelligence. You don’t have a
copying issue with them. And so, if this is
the case, then it gives rise to the importance
of collective brains. That actually, the
ability of a group to generate knowledge
and know-how and accumulate it
over time, and come up with more sophisticated
repertoires, and medical systems,
and technologies, depends on the size
and interconnectedness of the population. Larger populations that
are more interconnected runs– this process runs
faster and it runs farther. OK. And then finally,
for the last point, I’m going to argue that this
process– collective brains and this cultural
cumulus system– has actually driven much of
our species genetic evolution. So that if you want to
understand human evolution, you have to understand it as a
dual inheritance system, where culture is often the
driving force in much of our species
genetic evolution. Now the trick and in
approaching this– and I think one of the
reasons why there were maybe delays in getting where
I think I’m going– is that for a long time,
these two views were opposed. You had explanations
that were based either on genetic evolution on the
logic of natural selection to explain human
behavior, or you had cultural,
learning-based explanations. And in the book, I make the
case that the trick is– and this trick has been
around for 30 years or so now, but– is to take the
logic of natural selection and say, how does it shape
culture and cultural evolution? And specifically
by thinking about, how does natural selection
build learning machines? So how did it shape us to make
us more adaptive learners, to better extract
ideas, beliefs, and values from other
members of our social group. And also when to
say, well, now is the time to rely on
instinct, or now is the time to rely on
individual learning, on your own
independent experience. And one of the things that’s
interesting about humans is we seem to have gone
very far down this road. So we are much more inclined,
than any other species that does social learning, to
rely on the information that we acquire
from others, versus our own direct experience
and our own instincts. And I’ll give you
an example of that in the case of chili peppers. All right. And then the key move here is
that back to genetic evolution. So this builds stuff that
then affects this process. So you have a
feedback loop here. I wanted to give you
a little bit of sense about how you can take the
logic of natural selection, of genetic evolution, and
think about the evolution of our capacities for culture. So you want to
think about the cues that a learner might use to
shape what kinds of ideas, beliefs, and values
they pay attention to, who they pay attention to
in their social milieu, and how they integrate
different kinds of information. And all of those are kind
of semi-independent research projects that are going on in
the cultural evolutionary world now. My favorite one is
how people figure out who to pay attention to
in their social milieu. So both theory and now
quite a lot of evidence, evidence from babies,
evidence from young children, as well as all adults, suggest
that people rely on cues of skill and competence. So just– if you’re a
young hunter-gatherer and you want to figure out
how to be a good hunter, you might tend to pay
attention to the people whose arrows tend to hit the target
if they use bows and arrows. You might use cues of success. So in that case you
might preferentially attend to and learn from the
guy who tends to bring back the most big prey. So for example, I do
field work in Fiji– and this is a scene
from my site– and you can see as soon
as Lakema, the best underwater fish spear
fishermen in the village, came over to dismantle
this sea turtle– now this guy can’t take apart this
sea turtle because a hunter can’t carve up his own prey. So someone else had to do it. He tried and failed. Turtles are tough to get apart. But Lakema comes over and he
starts immediately tearing the thing apart like a pro,
and the kids crowd around because they’re going to
watch whatever Lakema does because he’s by far the
most prestigious hunter and– fishermen and
hunter in the village. Prestige is next. So if everybody’s
kind of playing this game of trying to
figure out who to learn from and who to pay
attention to, then you can actually use what other
people are doing as a way to figure out who you
want to learn from. So if you see certain
people receiving deference, people are giving
them the floor, it means those other people
think that someone is worthy of paying attention to. So you can use that as a cue
to help refine who you’re going to pay attention to. And we’ve done a
bunch of experiments on this among three and
four-year-old children. Age can also be a useful cue. So age is why
five-year-olds tend to want to hang around
and pay attention to the seven-year-olds because
they can scaffold themselves up to increasingly
more complex skills by not copying the
oldest guy, the best member of their community,
but rather by using age as a cue to scaffold
themselves up to increasingly more success. Another kind of cue is old age. So in small-scale societies,
not everyone gets to be old. So there’s actually
a filtering process going over the course
of people’s lifetimes, and if you get to be a senior
member, a mature member of a small-scale society, you
have actually shown something. There’s an information
content to the fact that you get to be
an older member. So people pay attention
to the wise, old elders because there are a few of them. And finally,
self-similarity can help you hone your learning
into things that might be useful to you later in life. So if the sexual division
of labor is at all old, and at least some
paleoanthropologists think it is, then males should
be inclined to copy males, and females should be
inclined to copy females. And if there were
ethnically-marked differences for over the course of
human evolutionary history, then we should use
cues of say dialect or dress to figure
out who to learn from. And there’s good
evidence for that as well, actually done
here in psychology. Now we know that
these things affect what a wide range of domain. So this is just a small
sampling of the domains that are important. Food preferences, so
which food do you like? If you want to get a kid to
eat a certain kind of food, put him at a table with
slightly older same-sex kids who love the food that you
want to get him to eat, and then he’ll
change his ranking. And there are some
interesting experiments on it. Telling him that he should eat
that food, not a good strategy. It affects things
like mate choice. My favorite is suicide. So people– when a
celebrity commits suicide, you get a– you can
get a rash of suicides. The more prestigious
the celebrity, the larger the
spike in suicides. And people match on sex,
and they match on ethnicity. So you can see the
cues even on suicide. Very bad for your
fitness, suicide is. All kinds of domains. So this seems to be something
that develops reliably. We found it in Fiji. We find in other– lots
of other societies. Develops early. You can see it already
operative in young children. And it’s automatic
and unconscious. So people are doing
it all the time and they don’t know
they’re doing it. Now this can give rise
to cultural adaptation. So individuals are
selective about who they’re paying attention to, so
it’s selection– selection and transmission. So you have these psychological
capacities that are selective, and that can build cultural
adaptations over time without anybody realizing it, so
zero intelligence adaptations, no intention, no design. I’m going to talk about
spices in a minute, but let me just
mention one other one. So in pre-Colombian–
in the Americas, corn was the staple
in many populations. But the populations that
relied heavily on corn had an odd custom of
putting a non-food substance into the recipe. So they would include burnt sea
shells, or ash from the fire, or natural lime sources. And this is important
because corn, if you just use it as a
staple and don’t treat it with this chemical
process that creates a chemical reaction that
releases the otherwise unavailable niacin, you get
a horrible disease called pellagra, and so these
populations were able to able to be reliance on corn
and not get pellagra. Now you might think, well
people can figure that out, that they’re going to pellagra,
they’re going to kind of work through it. We know that’s false because
we have historical experiments, both in the US and in Europe. So the Europeans take
corn over to Europe, and corn spreads widely, people
become dependent on corn. And of course, the
lower classes become entirely dependent on corn
because it’s the cheap staple. They all get pellagra. And this continues for
decades and decades before finally, a physician
named Joseph Goldberger figured it out. And he got– he was
massively opposed by the medical authorities
of the time who all thought it was pathogenic,
not this missing niacin issue. OK. And then you would
also get to read about how in Fuji
in food taboos– this is my own research–
project pregnant and breastfeeding women
from ciguatera toxin that you find in reef fish. So these are all non-conscious. People don’t have a causal
understanding of how they work, but yet they’re
highly adaptive to local environmental challenges. OK. Now spices. Spices are an odd thing. As far as I know, other
animals don’t do it. And we seem to use chemicals
that plants produce– and usually these
chemicals are to keep away mammals, or insects,
or fungi, or bacteria– and we put it on our foods. Now it turns out– so
this is work by Paul Sherman and Jennifer Billing. And they studied
these spices, and they looked at the most
common spices, things like garlic and
onions, and they looked at in the published
literature, how much they killed in terms of bacteria. And the most
commonly used spices are also the most effective
in killing bacteria. And lots and lots of spices
have some bacterial killing properties. And things like lime
and lemon, they’re not very good at killing
bacteria on their own, but they turn out
to be catalysts for other kinds of spices. So it looks like our recipes are
chemical concoctions that can reduce the pathogen in meat. Now one piece of evidence
that’s interesting is that if you look at the
mean annual temperature of different
countries, and you look at the number of these
pathogen-killing spices, the hotter the place,
the more the cuisine has pathogen-killing
spices in each recipe. And in fact, whether it has
one of these spices are not, in the hot climates,
every single meat recipe has some of the
pathogen-killing spices. Norway, not so many. So and I– and what I like
particularly about this is some of these chemicals
produced by plants are actually to keep mammals
away, so mammals like us. In the case of chili peppers,
it produces this capsaicin which is designed
to get mammals not to eat it so that birds
can take it and then disseminate the seeds further. So it’s trying to
keep mammals away. So chimps won’t eat
these chili peppers, and physicians recommend
to nursing mothers not to eat chili peppers
because the baby won’t like the milk as much
if some of the capsaicin gets into the milk. But if you grow up
in a place where they eat lots of chili peppers,
and you observe others eating and enjoying chili
peppers, you can turn the same
physiological sensation– which taps directly into
some of our pain system– turn it into pleasure. And you can come to enjoy
what you would otherwise experience as pain. There’s probably a lot
of things like that. All right. So once [INAUDIBLE] this is
when– these things can build cultural adaptations,
but the ability of the system to build
cultural adaptations turns out to depend
much more on the things about the population–
the size of the population and the
interconnectedness– that it does on the individual
intelligence of the agents. And I mean one of
the ways we explore this is by building simple
mathematical models. And you can increase the
intelligence of the agents by an order of
magnitude, and you get, instead of 1% of
the population doing it, you’ll get 10% of the
population doing it. But if you turn up the
interconnectedness, the whole thing explodes because
it has this kind of magnifying power law-type effect. So you get this
interconnectedness. Size and interconnectedness
is important for building this fancy cultural repertoire. But one interesting
implication of these models is that, if suddenly your
collective brain gets shrunk, somehow your population
shrinks, or it gets cut off, or your interconnectedness
goes down, you can actually begin to lose
some of this adaptive know-how. OK. So I want to show you a
little bit of evidence for these ideas. This is research done by
Rob Boyd and Michele Klein, and they wanted to look at the
relationship between population size and technological
complexity. But the problem
is on continents, it can be tricky
because it’s hard to say what the population is. Because continental populations
are all interconnected, especially in
small-scale societies, especially hunter-gathers. So they went to the Oceania,
where the island and the island group provides a kind of natural
way to carve off and say, that’s a population. You can assign a
population size to that. Now, they’re not saying that
these aren’t interconnected populations. They’re going to try to measure
that as a separate variable. So they went back
to the ethnographies and tried to calculate
the complexity of the marine foraging tool. So things for getting fish and–
my guess is mostly fishing– and they counted up the tools. So this is the population size
of the island or island group, and this is the number
of tools they found. And the larger the
population, the more tools– more different kinds of
marine foraging tools they had– and the more the
fancier those tools were. So they made this
measurement which is a borderline standard
measurement of techno units. It’s basically counting up the
separable parts of the tool. It’s not the best
measure, but it’s the best that anybody has come up with. And so, not only do those
societies have more tools, but they’re tools they
have are more complex. This is robust, all kinds
of ecological variables that you can try
to pop in there. You’ll also notice that they
measured a low-contact– so low amount of interconnectedness
with other islands– and high interconnectedness. And the high– the ones
with high interconnectedness tend to be above the line,
which means that they have even more tools, or
more complex tools, than you would expect
for their population. So the interconnectedness
is also doing some work. They’re getting re-energized
by the other islands. Oh so that fits the basic story. Now of course, if
fits the basic story, but could it fit lots of
other potential stories too. So I want to kind of
get a grip on this, so I worked with someone
who was a graduate student and then a post-doc here,
Michael Muthukrishna. And what we did was we
had 100 undergraduates, and they came into
the lab– we’re trying to do a
controlled experiment– and their job was to use a
difficult-to-use freeware, free software for editing
images called GIMP. And they had to reproduce
this supposedly complex image using the software. And they had a time limit. They got paid for
their performance. So the closer the image
that they produced was to this image, the
more money they got paid. They also had incentives
if their student– someone who they could
transmit information to– if their student did well. Now we had two treatments. And this is the key part. So this is the social
interconnectedness part. In one treatment,
information could just pass down a transmission chain
from one individual to another. So this individual
could learn from him, he could learn from
him, but that’s it. In this treatment,
any of these guys could learn from
any of these guys. So this is a fully
interconnected population. So it’s like you can learn
from anybody your village, or you can just learn
from your parents. And then after they
were done, they could create the best image
they could in the time they had, they could write
it up to two pages that would then get passed to
the next person down the line. So then the next generation
would get the target image, this, the model’s product–
something that hopefully looks kind of like this,
but as you’ll see, often doesn’t– and then
the write up– the tips, the tricks, any suggestions
that the teacher had. And then we can measure
their skill by similarity to the target. So this is 10 generations,
each laboratory generation, so one’s learning from
the previous generation. This blue line is the
mean image rating. So that’s how good the
image is over time. And you can see that the
one group, the group where you can only learn
from one model, they had a really good first
round, so they’re way up here, but then they drop. These guys had a
bad first round, but they eventually take
off, and they end up with a much higher skill
in this than these guys. Remember, everybody is randomly
assigned to a treatment groups, so there’s no reason to expect
there to be any intelligence or skill differences. But these guys get
this cumulative effect, and nothing in this group. So that seems to suggest that
there is some causality here that if you interconnect groups,
you get more rapid evolution. So it’s consistent
with the story that the Polynesian, or
the Oceania data fits. Now one of things– I’m
showing this experiment– there’s actually a whole class
of experiments like this– but I like this one because you
can look at a lot of the data right here on one screen. So this is where you can only
see one person [? priority. ?] And this is where
you can see five. And this first one
is the first round. So these guys don’t have
any teaching at all, right? They’re just trying
to figure it out. And then these guys
learn from these guys, and these guys learn from those
guys, et cetera, down the way. And you can see these guys
had a good first round, right? But then the second
round loses it. So these guys had
some good tips, but they didn’t go anywhere. Remember, you’re
trying to match this. These guys had a
terrible first one, these guys didn’t
even turn anything. Not too good on
the second round, but then this guy gets it,
and then everybody gets it, and then they start–
they gradually start rashing their way
up and things kick in, where these guys never
seem to go anywhere. By the time you get here,
the worst person in round 10 is better than the best
person in around 10 here. So you completely exceeded
the individual’s ability to figure this problem out. So this– because
this is an experiment, we can say the sociality,
at least in this experiment, caused an evolution of greater
skill over the laboratory generations. All right, now I want
to enter into thinking about how a shrinking population
might affect technology, and know-how, and this kind of
culture cultural adaptations. So I like to show this
to my undergraduates. It’s from an archaeologist
named Rhys Jones. And I ask him to say,
which of these stone– these are collections
of stone tools made by different groups
of hunter-gatherers– and so which one most recent
in time, closer to us in time, and which is the oldest? And what they typically
say is that these top ones are the most recent in
time, although these are quite different. So this is upper paleolithic,
35,000 years ago, and this is Australian
aboriginal stone tools, about 1700. So they say these
are the most recent, and they always say
these two are the oldest. Sometimes they’re not sure
which one’s the oldest. What’s interesting is that–
oh, sorry– these are very old. So that’s an old one chopper. These are Mousterian tools often
associated with Neanderthals. And these tools are Tasmanians. So these are contemporary. So they’re made by
anatomically modern humans, who are only separated by
150 miles of the Bass Strait. These guys are in Tasmania. These guys are in the mainlands. So there’s this interesting
pattern of tool technology. How can we possibly explain it? So let’s go into a little
bit about Tasmania. So the Europeans arrived
in Tasmania about 1642. Abel Tasman kind of sails
by the southern end. It’s an island of
all hunter-gatherers just like the rest of Australia
is, about 4,000 Tasmanians, 2/3 the size of Ireland. And it’s by far the
simplest technology that the Europeans ever
encountered as they expanded, so simpler than the Fuegians
in tip of Tierra del Fuego, simpler than the folks in
the Chathams– an island not too far from New Zealand. So it got even more interesting
when the archaeologist Rhys Jones began to dig back
into the history of Tasmania and look at the
archaeological records. So it seems that the
Tasmanians actually lost a lot of valuable
tools and technologies over the last 10,000 years. So 10,000 years ago,
Tasmanian archeology looks like mainland Australia. But then the two
begin to diverge with Australia
getting more complex and Tasmania getting simpler. So the Tasmania
either never developed or lost bone tools, cold-weather
clothing, hafted tools, nets, fishing spears, barb
spears, durable watercraft, and boomerangs. So you can see this is an
image of a Tasmanian raft. They actually had no paddles. And to cross rivers, women
would grease themselves down. And the husband and the kids, I
guess, would get on to the raft and she would swim it across. The grease protects her
from the cold in the water. And they use one-piece
wallaby skins– you saw that on the previous
slide– one-piece spears, and clubs for hunting. So they drank from
skulls pictured here. That’s from– that’s from
the Adelaide Museum actually. OK, so Rhys Jones
estimates about 24 items in their toolkit. Now, right just across the Bass
Strait in the control group, we have other group that
has the entire Tasmanian toolkit plus multi-prong
fishing spears, spear throwers, boomerangs,
mounted adzes, composite tools, a variety of nets for
different kinds of birds, fish, and wallabies, sewn bark
canoe, string bags, ground edge axes, wooden bowls for drinking. So you can see some
of these hafted tools. There’s their boomerang. These are different
kinds of nets they have for different
kinds of fish and depending on the ecological conditions. OK. So it’s a puzzle because
it’s very non-intuitive to realize that groups
could lose valuable stuff. How could that happen? How could you lose
something that’s useful? Well if we look back into
the kind of climatic history, a picture begins to emerge. So the last glacial maximum,
about 18,000 years ago– takes want to start warming up. By 12,000 years ago,
the seas are rising, and Tasmania is going from
a peninsula of Australia, where it’s attached to
the rest of Australia, to becoming its own island. By about 8,000 Tasmania’s
got quite a bit of ocean between itself
and mainland Australia, and contact ends
between the two. And it’s over that next period
of 8,000 to 10,000 years that all these losses occur,
that you have this shrunken population that’s no longer
attached to mainland Australia that just– it all
begins to ebb away. Meanwhile, in Victoria, not only
are things staying the same, but a group called
the Pama-Nyungan– because it’s a language
group– they’re expanding out of the North. And they have a fancy set
of rituals and institutions that allow them to stay
very interconnected. So this spreads down
South and technology begins to really
take off because they have new institutions that
make them more interconnected. But again, this is
an interesting bit of ethno-history, but
is there any causality? Can we get to the causality? So back to the lab. And this time I wanted to
give the 100 undergraduates something a little bit more
ecologically realistic. So it’s knot time. So we developed a
complex system of knots where they had to
use these knots, and assemble them, and then use
it to lift a chair successfully up into the air. Same setup as before, so
either one-to-one transmission or the group condition,
so interconnectedness. But we started with experts. So before the first group
started, we train them up, and we got them to a
high level of skill. And then we started the
transmission chains. And again, everybody’s
paid here for performance. Instead of passing
down written tips, I wanted something again,
more ecologically valid, but I want to control over it. So they– after they
did they’re knot making, they could make a video,
kind of a how-to video. And so the students
get the how-to video. And then again, we can measure
similarity to this original. And what we find is
that when there’s just one-to-one transmission, so not
very good interconnectedness– remember, they’re
initially skilled, so they have high knot skill–
you get a drop in the skill quickly, and then it
begins to level off here. The decline is slower, and
then it levels off here. And so you have a
Tasmanian-like effect, and it looks like this–
you have differences in steady-state skills. So it looks like– you
can’t say for sure– but it looks like this group is
going to pretty much stick here at about a skill of
60, and this group is going to stick here at about
30, 32, or something like that. So this is consistent with
the idea that there are these steady-state maximum that depend
on your group’s– your group size an interconnectedness. OK. So again, we know that
it’s not intelligence. This incentives are the
same in the two groups. The only thing different
is the interconnectedness, the sociality. So that’s relevant
using data from– well, from the laboratory and from
ethnographic and historically known cases, but I think
this picture extends back into human history. Now how far back
is a big question. In the book, I do my
best effort to attach it to the available
evidence and anchor it in what we know about
human evolutionary history. But I think that these
cultural– the products of this cultural
evolution actually drove the expansion of our brains
and shaped our anatomy in lots of ways. So let me sketch it out for you. So first you have
genetic evolution. It’s the first move. It develops sufficiently good
cultural learning capacities, or something about
sociality, that allows us to cross
this threshold and begin to accumulate
cultural evolution. Once cultural evolution begins
the accumulated process, it is going to– so it’s
a separate inheritance system– it’s going
to produce say tools, so say cooking and fire and some
cool looking stone tools, maybe some good wooden tools. But that means that if you’re
a learner in this world, there’s this really great stuff
you could get if you can only learn from other people. So that puts a pressure on
those who can learn better from other people. So it’s going to
create brains that are better at acquiring,
storing, and organizing cultural information. Once you have those
kinds of brains, that’s going to make this
whole system work better. So it’s going to
turn up the juice on the ability of this
system to generate stuff. Then you’re going to
get, say, tracking knowledge, water containers,
and better food processing. And that means that the learner
is faced with this world where this is a growing body of
really good stuff in the minds of other members of
his social group, if he can only acquire it. So pressure for brains are even
better at acquiring, storing, and organizing. So this can create an
autocatalytic runaway process which I think explains the
rapid expansion of human brains in about the last two
million years or so. Now, this system
eventually hits the stops because there are some
constraints in a primate’s physiology. Baby’s– the head
can only get so big. Natural selection
uses all these tricks to keep the baby’s head soft,
make it get born prematurely, get that baby’s head out of
there before it gets too big. So this hits the stops there. This process, of
course, can keep going– and it’s still going now,
ever faster and faster as it generates cultural information–
but then other things start to happen. So the division of labor
between males and females, I actually think is a
division of information. They’re splitting up
the info that one has to know in order to survive. Then, of course,
you eventually get a larger divisions of labor,
and then extra somatic storage of information, then computers. There’s a few steps in
between, but– So there’s that. Now that’s the information
that’s creating a selection pressure for brains to do this. But there’s also other
cultural products besides just the
information that do this. So let me give
you some examples. So the idea here is that these
are the cultural products, and then these
creates selections. So fire and cooking. Now my colleague,
Richard Wrangham, who’s right in the back
there, and his colleagues have persuasively
argued that humans are unusual for a
primate of our body size. Our digestive tract
seems underwhelming. So our gape’s are too small,
our teeth are too small, or stomachs too small,
our colons are too small. Our intestines are
probably about right, but there’s another–
there’s a story about that. The thing that’s
interesting though, is we don’t innately know
how to make fire or cook. So if I was to take all
of you very smart people and deposit you in
Western Massachusetts, there’d be no technology
and say, make fire and cook. You would not– nothing
would happen you unless you had some
training in how to make fire from
natural materials, you would just flounder. And same thing with cocking. There’s lots of ways to cook
poorly that actually makes the food less good to digest. So that seems to be a case where
the cultural spread of fire and cooking then generates
this downstream that Richard has documented so effectively. My other colleague,
Dan Lieberman, has argued
persuasively, I think, that humans are full
of running adaptations. So we have springy
arches, and strong calves, and nuchal ligaments
that allow our head to move independent
of our body that we don’t see other primates. And in particular, we have this
powerful sweating system which can cool us, cool us down. But if you look at this
system like an engineer, there’s a flaw. There’s a big gaping
hole in the system that there’s no
water tank because we have to cool
ourselves with sweat, but we need water
to run that system. And unlike camels and horses,
our ability to store water is quite limited. But if you look at the
way hunter-gathers who engage in persistence hunting
and chase down animals do it, they use cultural know-how. So they have water containers. So you actually saw some water
containers earlier in the talk. Australian Aborigines
keep these bamboo tubes, and they walk with or run
with the tubes of water. And there’s also
know-how about how to find roots that
bear water, and how to use little cues on the
surface to find water. So that’s the fuel for that. So it’s a culture-gene
co-evolutionary package that allows that
running stuff to go. And then what I’m
particularly interested in, and what I spend a lot
of time in the book on, is the psychological stuff. So humans seem to have
a particular system for acquiring knowledge
about plants and animals. We organize in a taxonomy. We can readily make inferences. So if you hear a story that
one tiger– that someone saw a tiger at
night hunting, you might naively assume that
well, only that’s just that one particular tiger–
Tigger, the tiger, that hunts at night. But because you have the
system, you immediately extend it to all tigers. It’s a good bet that if you
saw one tiger hunting a night, that all tigers hunt at night. And in fact, lions
might hunt at night too. So you can make a kind of jump. But it probably doesn’t tell
me anything about mice or ants. That’s all because you built
this kind of complex system. And there’s a bunch of
other cool features of that. We seem to have a
specialized system for thinking about
artifacts as separate from other non-living kind. So when little kids ask
questions about artifacts, they don’t know what it
does, but they kind of have a sense that
it’s an artifact, and so they want to
know what it does. Which is different
than if you show them something they don’t
identify as an artifact, they’re not interested
in its function. And in this case, they
tend to over imitate. So they copy be all the
details of how to use these things called artifacts. I’ve argued that to understand
human status psychology, that we have a
dominant psychology. That it’s kind of
similar to chimps so, you have high status because you
control force and force-threat. You can use coercion. You’re a subordinate
in a dominance hierarchy because you recognize
that someone controls force, force-threat, and coercion. But in humans, because we
can learn from each other, we also have prestige. And this is because knowledge
and know-how is unequally distributed amongst the
minds in your group. Some people know lots
of stuff, and so they tend to receive deference
because people are trying to learn from them,
and that gives rise to different emotional packages
and different kinds of status. So in order to understand
human status psychology, you need to understand
the gene culture stuff. This is actually
quite a long list. This is the last one I’ll do,
but cultural evolution also produces social norms. So once we can transmit
ideas about reputation, about how to judge
other’s behaviors and not just transmit
the behaviors themselves, then you get this
sticky situation where groups will
start doing something and their judging each other
based on how they do it, and the group can
get stuck there. And then as a
learner, you’ve got to do whatever it is the group
does because otherwise you’re going to get a bad reputation
or get punished in some way. And this gives rise
to a norm psychology where you expect the world
to be full of social rules, even if we don’t
know what they are. And we’re good at
inferring them. Even when sometimes
rules don’t exist, we kind of have a hair trigger
rule inference machinery. And this can also
lead to prosociality. So it’s the institutions
that are actually shaping our social psychology. I call that process
self-domestication. All right. Let me just wrap it up here. I’ve just given you a quick
tour of some of the ideas that I developed
in the book here. I’ll go through a few key ones. So we have to think of
our learning abilities as adaptations themselves. They’re honed to allow us
to effectively learn what we need to know in the world. But this gives rise to the
second system of culture and inheritance which
then becomes intertwined with our genetic
inheritance system, and you get gene
culture co-evolution. To understand our
ability species to adapt, you have to realize that we
have collective brains, that we solve these problems over
generations as a group because of our interconnectedness,
because it’s that system that
generates our ability to adapt to environments. And I mentioned some stuff
about how this can make us individually smarter. We produce these
cultural products which shape how we think. And it actually
shapes our brains. So for example, when
you learn to read, you get specialization
in your left hemisphere that non-literate
people don’t have. So your brain is
different if you come from a literate society,
and you’ve learned to read. Culture-driven
genetic evolution. So culture is part of our
biology in two different ways. First is the way
I just mentioned with the reading, where culture
shapes the environment we develop in, so through
that, it shapes our brains and our hormones. But of course, there’s
also the other way, which is by shaping
our genetic evolution. And that’s kind of the
long-term take on the book. And then finally, so to
really understand humans, you have to recognize that
we’re a culture species and that this goes deep into
our evolutionary history. Thanks.

3 thoughts on “How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter

  1. What physical adaptations did the brain have to under go in order to flourish in such a manner that math was able to be conceived as a useful cultural tool?

  2. Not quite as good as the Jonathan Haidt Lecture I watched a few days ago, but a good follow up to it nonetheless.

    The hotter the climate the more a culture includes pathogen killing spices, which explains why more northern cultures like those found in Ireland have such bland tasting foods. But he doesn't go on to explain how this cultural adaptation evolved.

    What this lecture suggests to me is that the internet is going to cause a rapid increase in the knowledge base of simpler and less developed cultures outside of the Western one.

    If humans can't even make fire without cultural knowledge being passed on then no wonder we fight so much to protect culture and improve it. We have evolved to rely deeply on culture rather than instinct. It seems to me that this has given us the edge evolutionarily, but also means we are at constant risk of losing valuable information that may become irretrievable if not saved and passed on to the next generation. So no more more book burnings please!

    He mentions that children show interest in "artifacts" and how they work. I wonder about children who don't show as much interest in hammers or trucks but are much more interested in intellectual things like reading or drawing.

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