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17
The Cultural Niche:
Why Social Learning Is Essential for
Human Adaptation
ROBERT BOYD,*§ PETER J. RICHERSON,†§ AND
JOSEPH HENRICH‡§
In the last 60,000 years humans have expanded across the globe and now
occupy a wider range than any other terrestrial species. Our ability to
successfully adapt to such a diverse range of habitats is often explained
in terms of our cognitive ability. Humans have relatively bigger brains
and more computing power than other animals, and this allows us to
figure out how to live in a wide range of environments. Here we argue
that humans may be smarter than other creatures, but none of us is nearly
smart enough to acquire all of the information necessary to survive in any
single habitat. In even the simplest foraging societies, people depend on a
vast array of tools, detailed bodies of local knowledge, and complex social
arrangements and often do not understand why these tools, beliefs, and
behaviors are adaptive. We owe our success to our uniquely developed
ability to learn from others. This capacity enables humans to gradually
accumulate information across generations and develop well-adapted
tools, beliefs, and practices that are too complex for any single individual
to invent during their lifetime.
*Department of Anthropology, University of California, Los Angeles, CA 90095; †Depart-
ment of Environmental Science and Policy, University of California, Davis, CA 95616; and
‡Departments of Psychology and Economics, University of British Columbia, Vancouver, BC,
Canada V6T 1Z4. §To whom correspondence may be addressed. E-mail: rboyd@anthro.ucla.
edu, pjricherson@ucdavis.edu, or henrich@psych.ubc.ca.
363
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I
n its brief evolutionary history, Homo sapiens has come to occupy
a larger range than any other terrestrial vertebrate species. Earlier
hominins, such as Homo heidelbergensis and Neanderthals, were lim-
ited to Africa and the temperate regions of southern Eurasia. Behavior-
ally modern humans were living in Africa by 70,000 years ago (Mourre
et al., 2010). Between 50,000 and 60,000 years ago, people left Africa,
crossing into southwest Asia (Klein, 2009). From there they spread rap -
idly through southern Eurasia, reaching Australia by 45,000 years ago,
a feat that only one other terrestrial mammal (a murid rodent) was able
to accomplish (Rowe et al., 2008). Soon after this, people penetrated far
north, reaching the latitude of Moscow by 40,000 years ago and the Arctic
Ocean by 30,000 years ago. People had spread almost as far south as the
southern tip of South America 13,000 years ago, and by 5,000 years ago
humans occupied virtually every terrestrial habitat except Antarctica
and some islands in Oceania (Klein, 2009). Even the most cosmopolitan
bird and mammal species have substantially smaller ranges (White et
al., 1994; Bruce, 1999; Wozencraft, 2005).
This global expansion required the rapid development of a vast range
of new knowledge, tools, and social arrangements. The people who moved
out of Africa were tropical foragers. Northern Eurasia was an immense
treeless steppe, relatively poor in plant resources and teeming with unfa -
miliar prey species. The people that roamed the steppe confronted a
hostile climate—temperatures fell to −20 °C for months at a time, and
there were often high winds. Surviving in such environments requires a
whole new suite of adaptations—tailored clothing (Gilligan, 2010), well-
engineered shelters, local knowledge about game, and techniques for
creating light and heat. This is just the northern Eurasian steppe; each of
the other environments occupied by modern human foragers presented a
different constellation of adaptive problems. Ethnographic and historical
accounts of 19th and 20th century foraging peoples make it clear that these
problems were solved through a diverse array of habitat-specific adapta -
tions (Kaplan et al., 2000). Although these adaptations were complex and
functionally integrated, they were mainly cultural, not genetic, adapta -
tions. Much evidence indicates, in fact, that local genetic changes have
played only a relatively small part in our ability to inhabit such a diverse
range of environments (Richerson and Boyd, 2005; Richerson et al., 2010).
Why are humans so much better at adapting to novel environments
than other mammals? There have been many different answers to this
question, but the most influential are rooted in the idea that people are
simply smarter than other creatures. We have bigger brains and more
computing power, and this allows us to adapt to a wider range of environ-
ments than other animals. One of the clearest statements of this hypothesis
comes from a series of papers by Tooby, Cosmides, Pinker, and collabora-
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The Cultural Niche / 365
tors (Tooby and DeVore, 1987; Cosmides and Tooby, 2001; Barrett et al.,
2007; Pinker, 2010). Other animals, they argue, are limited to what they call
“dedicated intelligence,” domain-specific learning and decision-making
mechanisms that are adapted to particular environments. Humans, by
contrast, have evolved “improvisational intelligence,” a suite of uniquely
flexible cognitive capacities that allow our species to acquire locally adap -
tive behavior in a wide range of environments. In short, we are adapted
to the “cognitive niche” (Tooby and DeVore, 1987; Pinker, 2010). These
capacities are augmented by our species’ ability to learn from each other,
especially using grammatical language.
This hypothesis flows from a nativist, modularist view of cognition.
Its central premise is that broad general problems are much more difficult
to solve than narrow specialized ones, and therefore the minds of all ani -
mals, including humans, are built of many special-purpose mechanisms
dedicated to solving specific adaptive problems that face particular spe-
cies. These mechanisms are modular in that they take inputs and generate
outputs relevant to problems in particular domains such as mate choice,
foraging, and the management of social relationships. These authors are
nativists because they believe that evolved mechanisms depend on a con -
siderable amount of innate information about the relationships between
cues and outcomes in particular domains for particular species. For exam -
ple, mechanisms that regulate decisions about mate choice in human
males may be based on the assumption that long-term mating is likely,
and thus selection favored a psychology that leads men to be attracted
to young women. Analogous mechanisms in chimpanzees, which do not
form long-term bonds, have produced a psychology that causes males
to prefer older females, perhaps because they are better mothers (Muller
et al., 2006). Mechanisms regulating social exchange are specialized in
other ways. The innate content is built up because learning and decision
mechanisms have been shaped by natural selection to solve the important
recurrent adaptive problems that confronted the species.
This view of cognitive evolution seems to preclude flexible, widely
applicable cognitive abilities; or, as Cosmides and Tooby put it, “on first
inspection, there appear to be only two biologically possible choices
for evolved minds: either general ineptitude or narrow competences”
(Cosmides and Tooby, 2001). However, these authors believe that humans,
and only humans, have undergone an evolutionary breakthrough that
gives them “the computational ability to improvise solutions in develop -
mental time to evolutionarily novel problems” (Barrett et al., 2007). The
key ability is the use of cause-and-effect reasoning to make inferences
about local environmental contingencies. As Pinker puts it,
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These inferences are played out internally in mental models of the world.
. . . It allows humans to invent tools, traps, and weapons, to extract
poisons and drugs from other animals and plants. . . . These cognitive
stratagems are devised on the fly in endless combinations suitable to the
local ecology. They arise by mental design and are deployed, tested, and
fine-tuned by feedback in the lifetime of individuals. . . . (Pinker, 2010,
pp 8993−8994)
These inferential capacities are augmented by a second evolutionary
innovation, the ability to learn from each other, a capacity that dramati -
cally lowers the cost of acquiring information necessary for local, contin -
gent adaptations.
It seems likely that the average human is smarter than the average
chimpanzee, at least in domains like planning, causal reasoning, and
theory of mind. However, we do not think this is sufficient to explain
our ecological success. The cognitive niche hypothesis overestimates the
extent to which individual human cognitive abilities allow people to
succeed in diverse environments and misunderstands the role that cul -
ture plays in a number of important ways. We suggest, instead, that our
uniquely developed ability to learn from others is absolutely crucial for
human ecological success. This capacity enables humans to gradually
accumulate information across generations and develop well-adapted
tools, beliefs, and practices that no individual could invent on their own.
We have entered the “cultural niche,” and our exploitation of this niche
has had a profound impact on the trajectory of human evolution. In the
remainder of this chapter, we will develop this argument in more detail.
CULTURE IS ESSENTIAL FOR HUMAN ADAPTATION
It is easy to underestimate the scope, sophistication, and importance
of the pool of culturally transmitted information that supports human
subsistence, even in what seem to be the “simplest” foraging societies.
The archaeological record makes it clear that modern humans adapted
to life above the Arctic Circle early in their expansion but tells us little
about their way of life. However, ethnographic studies of the Netsilik and
Copper Inuit, collectively known as the Central Inuit, give us a sense of the
complexity of the adaptations that allow foragers to thrive in the Arctic.
These people occupy a habitat that is harsh and unproductive, even by
Arctic standards. Their groups were small, and their lifeways were simple
compared with foragers living on the coasts of Alaska and Greenland.
To focus your mind on the crucial adaptive challenges, imagine that you
are marooned on a beach on the coast of King William Island (68.935N,
98.89W). It is November and it is very cold.
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The Cultural Niche / 367
Your first problem is to stay warm. Monthly average temperatures in
the winter months are between −25 °C and −35 °C. Even well-acclimatized
people rapidly succumb to hypothermia below −1 °C, so you need warm
clothes. If there were no wind and you could remain motionless, a cloak
would do, but this is a windy place and you need to hunt, so you will
need well-tailored clothes (Gilligan, 2010). In the winter, the Central Inuit
wore elaborately constructed parkas and pants (Issenman, 1997). The best
were made from caribou skins harvested in the fall. Caribou skins insu -
late better than seal or polar bear fur because the individual hairs have
an unusual air-filled structure, something like bubble wrap (Otak, 2005).
Caribou skins harvested in autumn have fur that is just the right thickness.
Hides were repeatedly stretched, scraped, moistened, and then stretched
again to yield pliable skins (Meeks and Cartwright, 2005). Parkas were
assembled from multiple pieces to create a bell shape that captures heat,
while also allowing moisture to dissipate when the hood is thrown back.
Hoods were ruffed with a strip of fur taken from a wolverine’s shoulders
because its variable length makes it easier to clear the hoarfrost. Winter
footwear was constructed with many layers: first the alirsiik, furlined
caribou stockings, then the ilupirquk, short lightweight stockings with the
fur outside, then a pair of pinirait, heavier stockings with the fur to the
outside, then kamiik, boots with the fur outside, and finally tuqtuqutiq,
short heavy double-soled boots of caribou skin. Clothing was stitched
together with fine thread made from sinew taken from around the ver-
tebrae of caribou. The sinew had to be cleaned, scraped, shredded, and
twisted to make thread. Several different kinds of stitches were used for
different kinds of seams. A complicated double stitch was used to make
footwear waterproof. To make these stitches, Central Inuit women used
fine bone needles that made holes that were smaller in diameter than the
thread (Issenman, 1997).
Not even the best clothing is enough to protect you from winter
storms, so you need shelter. During the winter most Inuit lived in substan -
tial driftwood and sod houses, but the Central Inuit wintered on the sea
ice, living in snow houses. These round vaulted structures were ≈3 m high,
made of snow blocks cut with a serrated bone knife. The central room was
built above a pit, with platforms for sleeping, and a long entrance tunnel
below the level of the main room with several low doors to prevent heat
loss. The walls were usually lined with skins suspended from toggles on
the outside of the snow house. This design allowed the snow walls to stay
near freezing, while the inside of the snow house could reach temperatures
of 10−20 °C (Damas, 1984).
You need a source of heat and light in your snow house, for cooking
and for melting sea ice for water. You cannot use wood fires because there
are no trees. Instead, Arctic peoples carved lamps from soapstone and
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fueled them with rendered seal fat. These lamps were made from oblong
stones between 30 cm and 1 m long; a shallow, sharp-sided depression
was carved from the surface of the stone, and the lamp was equipped with
a long, curtain-like wick made of moss. A well-managed lamp burned
without producing any soot (Issenman, 1997).
You also need food. Plants are easy to gather, but for most of the year
this is not an option in the Arctic. During the winter, the Central Inuit
hunted seals, mainly by ambushing them at their breathing holes. When
the sea ice begins to freeze, seals claw a number of breathing holes in the
ice within their home ranges. As the ice thickens, they maintain these
openings, which form conical chambers under the ice. The Inuit camped in
snowy spots near the seals’ breathing holes. The ice must be covered with
snow to prevent the seals from hearing the hunters’ footsteps and evading
them. Inuit hunted in teams, monitoring as many holes as possible. The
primary tool was a harpoon approximately 1.5 m long. Both the main shaft
and foreshaft were carved from antler. On the tip was a detachable toggle
harpoon head connected to a heavy braided sinew line. The other end of
the harpoon was made from polar bear bone honed to a sharp point. At
each hole, the hunter opened the hard icy covering using the end of the
harpoon, smelled the interior to make sure it was still in use, and then
used a long, thin, curved piece of caribou antler with a rounded nob on
one end to investigate the chamber’s shape and plan his thrust. The hunter
carefully covered most of the hole with snow and tethered a bit of down
over the remaining opening. Then, the hunter waited motionless in the
frigid darkness, sometimes for hours. When the seal’s arrival disturbed
the down, the hunter struck downward with all his weight. If he speared
the seal, he held fast to the line connected to his harpoon’s point; the seal
soon tired and could be hauled onto the ice (Balikci, 1989).
During the high summer, the Central Inuit used the leister, a special
three-pronged spear with a sharp central spike and two hinged, backward-
facing points, to harvest Arctic char in large numbers. Later in summer
and the fall, they shifted to caribou hunting. On land, caribou were mainly
stalked or driven into ambush, and kills had to be made from a substantial
distance. This required a bow with the power to propel a heavy arrow
at high velocity. The simplest way to accomplish this is to make a long
bow using a dense elastic wood like yew or osage orange, a design com -
mon in South America, Eastern North America, Africa, and Europe. This
solution was not available to the Inuit, who had only driftwood (mainly
spruce), horn, and antler available. Instead, they made short bows and
used every bowyer’s trick to increase their power. A bow can be made
more powerful by adding wood to the limbs. However, making the bow
thicker increases the stress within the bow, leading to catastrophic and
dangerous failure. This problem is exacerbated in short bows because the
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The Cultural Niche / 369
curvature is greater. Instead, the Inuit made bows that were thin front
to back, wide near the center, and tapering toward the tips. These bows
were also recurved, meaning that the unbraced bow formed a backward
“C” shape. Bracing the bow leads to a compound curve, a geometry that
stores more potential energy. Finally, the Inuit constructed a unique form
of composite bow. When a bow is bent, the back (the side away from the
archer) is stretched, whereas the belly (the side closer to the archer) is
compressed. Wood, horn, and antler are stronger in compression than
tension, so the ability of a bow to sustain strong bending forces can be
enhanced by adding a material that is strong in tension to the back of the
bow. In central Asia and western North America, sinew was glued to the
back of the bow to strengthen short bows for use on horseback. The Inuit
lashed a woven web of sinew to the backs of their bows, probably because
they had no glues that would work in the moist, cold conditions of the
Arctic (Mason, 2007).
This sampler of Inuit lifeways represents only a tiny fraction of the
immense amount of habitat-specific knowledge that is necessary for
humans to survive and prosper in the Central Arctic. To stay warm and
get enough to eat, you have to know how to make and use clothes, snow
houses, lamps, harpoons, leisters, and bows. We have omitted other cru-
cial tools like kayaks, dog sleds, and sun goggles, and of course, we have
had to omit most of the details necessary to make and use the tools we
did mention. Moreover, there is still much more you have to know to stay
alive. Predicting storms, understanding the habits of game species, mak -
ing baskets, building sledges, and managing dogs—all require extensive
knowledge. Traveling on ice is essential, but also treacherous, and there
is much to know about how the current temperature, recent weather, and
the color and texture of the ice tell you where and when it is safe to travel.
[Nelson (1969) devotes four chapters to ice lore in his book on hunting
among the Inupiaq of northern Alaska.]
So, here is the question: Do you think that you could acquire all of
the local knowledge necessary to survive in the Arctic on your own? If
superior cognitive ability alone is what allows humans to adapt to diverse
habitats, then it should be possible. Moreover, to a first approximation,
this is the only way that other animals have to learn about their envi-
ronments—they must rely mainly on innate information and individual
experience to figure out how to find food, build shelters, and in some
cases to make tools. It is true that some species have simple traditions,
probably maintained by learning mechanisms like stimulus enhancement
and emulation. However, in every case, the traditions involve behaviors
that individuals can and do learn on their own, or combine a handful
of elements learned by multiple individuals (Tennie et al., 2009). There
are no convincing examples in which social learning allows the gradual
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cumulative cultural evolution of complex, locally adaptive behaviors that
individuals could not learn on their own.
Could you make it? We don’t think so.
Two different kinds of natural experiments support the intuition that
forager adaptations are beyond the inventive capacities of individuals.
The first, which might be called “the lost European explorer experiment,”
has been repeated many times during the past several centuries. Typi -
cally some explorers get stranded in an unfamiliar habitat in which an
indigenous population is flourishing. Despite desperate efforts and ample
learning time, the explorers die or suffer terribly owing to the lack of
crucial information about how to adapt to the habitat. If they survive, it
is often due to the hospitality of the indigenous population. The Franklin
Expedition of 1845–1846 provides a good example (Lambert, 2011). Sir
John Franklin, a Fellow of the Royal Society and an experienced Arctic
traveler, set out with two ships to explore the northern coast of North
America and find the Northwest Passage. It was the best-equipped expedi-
tion in the history of British polar exploration, furnished with an extensive
library, manned by a select crew, and stocked with a 3-year supply of food.
The expedition spent the winter of 1846 at King William Island, where it
became trapped in the ice. When food ran short, the explorers abandoned
their ships and attempted to escape on foot. Everyone eventually perished
from starvation and scurvy, perhaps exacerbated by lead poisoning from
their tinned food.
King William Island is the heart of Netsilik territory, and the Netsilik
have lived there for almost a millennium. King William Island is rich in
animal resources—the main harbor is named Uqsuqtuuq which means
“lots of fat.” The British sailors starved because they did not have the
necessary local knowledge and, despite being endowed with the same
improvisational intelligence as the Inuit and having 2 years to use this
intelligence, failed to learn the skills necessary to subsist in this habitat.
Interestingly, the Norwegian explorer Roald Amundsen spent two winters
on King William Island in 1903−1904. Amundsen sought out the Netsilik
and learned from them how to make skin clothing, hunt seals, and manage
dog sleds. He and his crew survived and completed the first successful
traverse of the Northwest Passage. Later he would put these Inuit skills
to good use in his race with Scott to the South Pole. Results from this lost
European explorer experiment, and many others, suggest that intelligence
alone is not enough. For a similar discussion of the ill-fated Burke and
Wills expedition into the Australian outback, see Henrich and McElreath
(2003).
A second line of evidence comes from the loss of beneficial technolo-
gies in small, isolated populations. For instance, the Tasmanian tool kit
gradually lost complexity after isolation from mainland Australia at the
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The Cultural Niche / 371
end of the Holocene (Henrich, 2004b). Other Pacific island groups have
apparently lost useful technologies, such as canoes, pottery, and the bow
and arrow (Kline and Boyd, 2010). The best documented example comes
from the isolated Polar Inuit of northwest Greenland. Explorers Elisha
Kane and Isaac Hayes wintered with the Polar Inuit in 1853 and 1861,
respectively, and reported that the Polar Inuit lacked kayaks, leisters, and
bows and arrows and that their snow houses did not have the long heat-
saving entryways that were seen among other Inuit populations. They
could not hunt caribou, could only hunt seals during part of the year, and
were unable to harvest Arctic char efficiently, although char were plentiful
in local streams (Mary-Rousselière, 1996). Apparently the population was
struck by an epidemic in the 1820s that carried away the older, knowledge-
able members of the group, and according to custom, their possessions
had to be buried with them (Rasmussen, 1908). The Polar Inuit lived
without these tools until about 1862, when they were visited by a group
of Inuit who migrated to Greenland from Baffin Island (Rasmussen, 1908;
Mary-Rousselière, 1996). There is every reason to believe that these tools
would have been useful between 1820 and 1862. The Polar Inuit popula-
tion declined during this period, and the tools were immediately adopted
once they were reintroduced. After their introduction, population size
increased. It is also telling that the kayaks used by the Polar Inuit around
the turn of the century closely resemble the large, beamy kayaks used by
Baffin Island Inuit and not the small sleek kayaks of the West Greenland
Inuit. Over the next half century the Polar Inuit kayak design converged
back to the West Greenland design (Golden, 2006). If this inference is
correct it means that for 40 years (nearly two generations) the Polar Inuit
could have benefitted from the lost knowledge. Moreover, they collectively
remembered kayaks, leisters, and bows and arrows, but did not know how
to make them and could not recreate that knowledge.
CULTURAL ADAPTATION IS A POPULATION PROCESS
We think that this body of evidence rules out the idea that superior
cognitive ability alone explains human adaptability; the ability to cumu-
latively learn from others must play a crucial role. Although advocates
of the cognitive niche hypothesis focus on cognition, they do not ignore
social learning. They argue that the ability to learn from others reduces
the average cost of acquiring locally adaptive information. For example,
Barrett et al. (2007) write:
Cognitive mechanisms underlying cultural transmission coevolved with
improvisational intelligence, distributing the costs of the acquisition of
nonrivalrous information over a much greater number of individuals, and
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allowing its cost to be amortized over a much greater number of advanta-
geous events and generations. Unlike other species, cultural transmission
in humans results in a ratchet-like accumulation of knowledge. (p 244)
On the surface this seems to be a logical argument. It may be costly for
individuals using improvisational intelligence to discover locally adaptive
information, but once it is acquired, others can get it by teaching or imita -
tion at relatively low cost. As a result, social learning acts to spread the
cost of innovations over all who benefit. Innovations accumulate, leading
to an accumulation of knowledge.
However, this reasoning is mistaken. It is probably true that learning
from others either by teaching or imitation is usually cheaper than learn-
ing on your own. It is like cheating on a test: you do as well as the person
you copy from but avoid all that tedious studying. However, evolution -
ary models show that if this is the only benefit of social learning, there
will be no increase in the ability of the population to adapt (Rogers, 1988;
Boyd and Richerson, 1995; Lehmann et al., 2010; Rendell et al., 2010). This
surprising result emerges from the coevolutionary processes that affect
the kinds of behaviors that are available to imitate and the psychology
that controls learning and imitation. These evolutionary models of social
learning rest on two assumptions. First, the propensities to learn and to
imitate are part of an evolved psychology shaped by natural selection. This
means that the balance between learning and imitating will be governed
by the relative fitness of the two modes of behavior—the average fitness
of the population is irrelevant. When few individuals imitate, imitators
will acquire the locally adaptive behavior with the same probability as
individual learners. Because they do not pay the cost of learning, imitators
have higher fitness, and the propensity to imitate spreads. As the num-
ber of imitators increases, some imitate individuals who imitated other
individuals, who imitated other individuals, and so on until the chain is
rooted in someone who extracted the information from the environment.
As the fraction of imitators in the population increases, these chains extend
further.
The second assumption is that the environment varies in time or
space. This means that as chains of imitation get longer, there is a greater
chance that the learner who roots the chain learned in a different envi-
ronment than the current environment, either because the environment
has changed since then or because someone along the chain migrated
from a different environment. The upshot is that on average imitators
will be less likely to acquire the locally adaptive behavior than learners.
The propensity to imitate will continue to increase until this reduction in
fitness exactly balances the benefit of avoiding the costs of learning. At
evolutionary equilibrium, the population has the same average fitness as
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The Cultural Niche / 373
a population without any imitation. There will be no increase in the abil -
ity to adapt to varying environments, and cumulative cultural adaptation
will not occur.
Although this treatment is very simple, the basic result holds in more
realistic models. The primary insight that emerges from these models
is that imitation is a form of free riding—imitators scrounge informa-
tion without producing anything of value. Free riders increase until they
destroy the benefits of free riding. Realistic levels of relatedness among
models and imitators do not qualitatively change the result (Lehmann
et al., 2010). The advocates of the cognitive niche hypothesis err because
they take it as unproblematic that once a beneficial innovation arises, it
will spread, and as a result, the capacities for imitation will be favored by
selection. However, to understand the evolution of social learning psy-
chology you have to know what is available to learn, and this in turn is
affected by the nature of the learning psychology. If imitators are simply
information scroungers, then they will spread until selection no longer
favors imitation.
Thinking about the coevolution of the cultural pool of observable
behavior and the genes that control the individual and cultural learn-
ing suggests that cultural learning can increase average fitness only if
it increases the ability of the population to create adaptive information
(Boyd and Richerson, 1995). The propensity to imitate evolves because
it is directly beneficial to the individual, but it may, nonetheless, also
benefit the population as a side effect. We have thought of three ways in
which this could happen. First, cultural learning can allow individuals
to learn selectively—using environmental cues when they provide clear
guidance and learning from others when they do not. Second, cultural
learning allows the gradual accumulation of small improvements, and
if small improvements are cheaper than big ones, cultural learning can
reduce the population’s learning costs. Finally, by comparing “teachers”
and learning selectively from those that seem most successful, “pupils”
can acquire adaptive information without making any inferences based
on environmental cues. If individuals acquire information from multiple
teachers and recombine this information, this process can create complex
cultural adaptations without any intelligence, save that required to dis-
tinguish among more- and less-successful teachers.
The ability to learn or imitate selectively is advantageous because
opportunities to learn from experience or by observation of the world
vary. For example, a rare chance observation might allow a hunter to
associate a particular spoor with a wounded polar bear, or to link the
color and texture of ice with its stability on windy days just after a thaw.
Such rare cues allow accurate low-cost inferences about the environment.
However, most individuals will not observe these cues, and thus making
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the same inference will be much more difficult for them. Organisms that
cannot imitate must rely on individual learning, even when it is difficult
and error prone. They are stuck with whatever information that nature
offers. In contrast, an organism capable of cultural learning can afford
to be choosy, learning individually when it is cheap and accurate, and
relying on cultural learning when environmental information is costly or
inaccurate. We have shown (Boyd and Richerson, 1988, 1995) that selection
can lead to a psychology that causes most individuals to rely on cultural
learning most of the time, and also simultaneously increases the average
fitness of the population relative to the fitness of a population that does
not rely on cultural information. These models assume that our learning
psychology has a genetically heritable “information quality threshold”
that governs whether an individual relies on inferences from environ-
mental cues or learns from others. Individuals with a low information
quality threshold rely on even poor cues, whereas individuals with a high
threshold usually imitate. As the mean information quality threshold in
the population increases, the fitness of learners increases because they are
more likely to make accurate or low-cost inferences. At the same time, the
frequency of imitators also increases. As a consequence, the population
does not keep up with environmental changes as well as a population of
individual learners. Eventually, an equilibrium emerges in which indi -
viduals deploy both individual and cultural learning in an optimal mix.
At this equilibrium, the average fitness of the population is higher than in
an ancestral population lacking cultural learning. When most individuals
in the population observe accurate environmental cues, the equilibrium
threshold is low, individual learning predominates, and culture plays little
role. However, when it is usually difficult for people to learn individu -
ally, the equilibrium threshold is high, and most imitate, even when the
environmental cues that they do observe indicate a different behavior than
the one they acquire by cultural learning. We take the evidence on Inuit
adaptations as indicating that many of the problems that faced the Inuit
are far too difficult for most individuals to solve. As a result, we interpret
this logic as predicting that selection should have favored a psychology
that causes individuals to rely heavily on cultural learning.
The ability to learn culturally can also raise the average fitness of a
population by allowing acquired improvements to accumulate from one
generation to the next. Many kinds of traits admit successive improve -
ments toward some optimum. Bows vary in many dimensions that affect
performance—such as length, width, cross section, taper, and degree of
recurve. It is typically more difficult to make large improvements by trial
and error than small ones for the same reasons that Fisher (1930) identified
in his “geometric model” of genetic adaptation. In a small neighborhood
in design space, the performance surface is approximately flat, so that
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even if small changes are made at random, half of them will increase the
payoff (unless the design is already at the optimum). Large changes will
improve things only if they are in the small cone that includes the distant
optimum. Thus, we expect it to be much harder to design a useful bow
from scratch than to tinker with the dimensions of a reasonably good
bow. Now, imagine that the environment varies, so that different bows
are optimal in different environments, perhaps because the kind of wood
available varies. Sometimes a long bow with a round cross section is best,
other times a short flat wide bow is best. Organisms that cannot imitate
must start with whatever initial guess is provided by their genotype. Over
their lifetimes, they can learn and improve their bow. However, when they
die, these improvements disappear with them, and their offspring must
begin again at the genetically inherited initial guess. In contrast, cultural
species can learn how to make bows from others after these have been
improved by experience. Therefore, cultural learners start their search
closer to the best design than pure individual learners and can invest in
further improvements. Then, they can transmit those improvements to the
grandkids, and so on down through the generations until quite sophisti -
cated artifacts evolve. Historians of technology have demonstrated how
this step-by-step improvement gradually diversifies and improves tools
and other artifacts (Basalla, 1988; Petroski, 1992). Even “great insights”
often result from lucky accidents or the recombination of elements from
different technological traditions rather than the work of a creative genius
who buckles down and racks his brain (Henrich, 2010; S. Johnson, 2010).
The evolution of kayak keels by West Greenland Inuit provides an
instructive example of how innovations arise and spread (Scavenius,
1975). When hunting marine mammals from a kayak, Inuit hunters always
paddled their kayak hard toward the prey, then picked up their harpoon
and hurled it directly over the bow. This increased the momentum trans-
ferred to the harpoon and prevented capsizing. When firearms first spread
in West Greenland, the Inuit found that they could not pick up and aim
their guns before the kayak veered off course, and thus could only use
them from land or ice floes. In 1824, a prominent Inuit hunter named Jens
Reimer began to experiment with methods to stabilize kayaks for firearm
use. He tried trailing a line behind the kayak, but this did not work. He
then fastened a partially submerged wooden plate to the kayak’s stern,
in imitation of the rudders of European ships. This did not work very
well either—it was noisy, and the fastenings tended to fail. Nonetheless,
a number of younger hunters imitated Reimer, perhaps owing to his local
success and prestige. They were not able to produce a quality ayût (the
Greenlandic word for both a ship’s rudder and a kayak keel), and out
of “bashfulness” (Scavenius, 1975, p 27) hid their crude rudders under
the waterline. They soon discovered that this unintentional innovation
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allowed them to use guns from their kayaks, and over the next 50 years
the ayût underwent a series of further small improvements, eventually
creating the modern form.
Finally, if learners can compare the success of individuals modeling
different behaviors, then a propensity to imitate the successful can lead to
the spread of traits that are correlated with success, even though imitators
have no causal understanding of the connection. This is obvious when the
scope of traits being compared is narrow. You see that your uncle’s bow
shoots farther than yours and notice that it is thicker, but less tapered, and
uses a different plait for attaching the sinew. You copy all three traits, even
though in reality it was just the plaiting that made the difference. As long
as there is a reliable statistical correlation between plaiting and power,
plaiting form trait will change so as to increase power. Causal understand-
ing is helpful because it permits the exclusion of irrelevant traits like the
bow’s color. However, causal understanding need not be very precise as
long as the correlation is reliable. Copying irrelevant traits like thickness or
color will only add noise to the process. By recombining different compo -
nents of technology from different but still successful individuals, copiers
can produce both novel and increasingly adaptive tools and techniques
over generations, without any improvisational insights. An Inuit might
copy the bow design from the best bowyer in his community but adopt the
sinew plaiting used by the best hunter in a neighboring community. The
result could be a better bow than anyone made in the previous generation
without anyone inventing anything new.
Consistent with this, laboratory and field evidence suggests that both
children and adults are predisposed to copy a wide range of traits from
successful or prestigious people (Henrich and Gil-White, 2001). Advertis -
ers clearly know this. After all, what does Michael Jordan really know
about underwear? Recent work in developmental psychology shows that
young children readily attend to cues of reliability, success, confidence,
and attention when choosing who to learn from (Birch et al., 2008, 2010).
Even infants selectively attend to knowledgeable adults rather than their
own mothers in novel situations (Stenberg, 2009). This feature of our cul -
tural learning psychology fits a priori evolutionary predictions, emerges
spontaneously in experiments, develops early without instruction, and
operates largely outside conscious awareness.
These models predict that an adaptive evolved psychology will often
cause individuals to acquire the behaviors they observe used by in others
even though inferences based on environmental cues suggest that alterna -
tive behaviors would be better. In a species capable of acquiring behavior
by teaching or imitation, individuals are exposed to two different kinds
of cues that they can use to solve local adaptive problems. Like any other
organism, they can make inferences based on cues from the environment.
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However, they also observe the behaviors of a sample of their population.
When most individuals can solve the adaptive problem using environ -
mental cues alone, the models predict that an optimal learning psychology
will result in social learning playing a significant but relatively modest
role. Many people will rely on their own inferences, but some will copy to
avoid learning costs. However, often only a minority will be able to solve
the adaptive problem on the basis of environmental cues alone, because
the appropriate environmental cues are rare or the adaptive problem is
too complex. Then, if the environment is not too variable, an adaptive
psychology will evolve in which most people ignore environmental cues
and adopt behaviors that are common in the sample of the population they
observe. They modify these behaviors rarely, or only at the margin, and as
a result local adaptations evolve gradually often over many generations.
EVIDENCE FOR CULTURAL ADAPTATION
The cultural niche hypothesis and the cognitive niche hypothesis make
sharply different predictions about how local adaptations are acquired and
understood. The cognitive niche hypothesis posits that technologies are
adaptive because improvisational intelligence allows some individuals to
figure out how they work and why they are better than alternatives. These
acquired understandings of the world are then shared, allowing others to
acquire the same causal understanding without costly individual investi -
gation. In contrast, we argue that cultural evolution operating over gen-
erations has gradually accumulated and recombined adaptive elements,
eventually creating adaptive packages beyond the causal understanding
of the individuals who use them. In some cases elements of causal under-
standing may be passed along, but this is not necessary. Often individuals
will have no idea why certain elements are included in a design, nor any
notion of whether alternative designs would be better. We expect cultural
learners to first acquire the local practices and occasionally experiment
or modify them. At times this will mean that cultural learning will over-
rule their direct experience, evolved motivations, or reliably developing
intuitions.
Several lines of evidence support the cultural learning hypothesis.
The anthropological literature on child development (Lancy, 1996,
2009, 2010) indicates that children and adolescents acquire most of their
cultural information by learning from older individuals who typically
discourage questions from young learners and rarely provide causal
explanations of their behavior. Kids practice adult behaviors, often using
toy versions of adult tools, during mixed-age play, and little experimen -
tation is observed, except that necessary to master the adult repertoire
(MacDonald, 2007; Hewlett et al., 2011).
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The reliance of young learners on carefully observing and imitating
the local repertoires revealed in the anthropological record converges with
recent experiments on imitation (Lyons et al., 2007; Nielsen and Tomaselli,
2010). In these experiments, an adult performs a behavior like opening a
complex puzzle box to get a reward. The adult’s behavior includes both
necessary and unnecessary actions. A subject, either a child or a chim -
panzee, observes the behavior. Children’s performance on such tasks in
both western and small-scale societies differs in important ways from that
of chimpanzees. Children accurately copy all steps, including steps that
direct visual inspection would suggest are unnecessary. Children seem to
implicitly assume that if the model performed an action, it was probably
important, even if they do not understand why. Chimpanzees do not seem
to make this assumption; they mainly skip the unnecessary steps, leading
them to develop more efficient repertoires than children (Whiten et al.,
2009) in these experimental settings.
Many examples indicate that people often do not understand how
adaptive practices work or why they are effective. For example, in the New
World, the traditional use of chili peppers in meat recipes likely protected
people from foodborne pathogens (Billing and Sherman, 1998). This use of
chili peppers is particularly interesting because they are inherently unpal -
atable. Peppers contain capsaicin, a chemical defense evolved in the genus
Capsicum to prevent mammals (especially rodents) from eating their fruits.
Nonhuman primates and human infants find peppers aversive because
capsaicin stimulates pain receptors in the mouth. Efforts to inculcate a
taste for chilies in rats using reinforcement procedures have failed (Rozin
et al., 1979). However, human food preferences are heavily influenced
by the preferences of those around us (Birch, 1987), so we overcome our
innate aversion and actually learn to enjoy chilies. Psychological research
indicates that people do not get accustomed to the chemical burning sen -
sation. Instead, observational learning leads people to reinterpret their
pain as pleasure or excitement (Rozin et al., 1981). So, New World peoples
learned to appropriately use and enjoy chili peppers without understand -
ing their antimicrobial properties, and to do this they had to overcome an
instinctive aversion that we share with other mammals.
Fijian food taboos provide another example of this process. Many
marine species in the Fijian diet contain toxins, which are particularly
dangerous for pregnant women and perhaps nursing infants. Food taboos
targeting these species during pregnancy and lactation prohibit women
from eating these species and reduce the incidence of fish poisoning
during this period. Although women in these communities all share the
same food taboos, they offer quite different causal explanations for them,
and little information is exchanged among women save for the taboos
themselves (Henrich and Henrich, 2011). The taboos are learned and are
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not related to pregnancy sickness aversions. Analyses of the transmission
pathways for these taboos indicate the adaptive pattern is sustained by
selective learning from prestigious women.
CULTURE AND MALADAPTATION
Cultural adaptation comes with a built-in tradeoff. The cumulative
cultural evolution of complex, hard-to-learn adaptations requires indi -
viduals to adopt the behavior of those around them even if it conflicts with
their own inferences. However, this same propensity will cause individu-
als to acquire any common behavior as long as it is not clearly contradicted
by their own inferences. This means that if there are cognitive or social
processes that make maladaptive ideas common, and these ideas are not
patently false or harmful, people will adopt these ideas as well. Moreover,
it is clear that several such processes exist. Here are a couple of examples.
For a longer discussion, see Richerson and Boyd (2005).
Weak Cognitive Biases Can Favor the Spread of Maladaptive Beliefs
or Practices over Generations
Laboratory diffusion chain studies clearly document that biases that
have undetectable effects on individual decisions can have very strong
effects when iterated over “generations” in the laboratory (Beppu and
Griffiths, 2009). The same effect may lead to the spread of false beliefs in
natural populations. For example, Boyer (2002) argues that a number of
cognitive biases explain the spread of supernatural beliefs and account for
the widespread occurrence of folktales about ghosts and zombies.
Adaptive Social Learning Biases Can Lead to Maladaptive Outcomes
A model’s attributes provide indirect evidence about whether it is
useful to imitate her. If she is successful, then by imitating her you can
increase your chances of acquiring traits that gave rise to her success. If
she is more similar to you than alternative models, her behavior may work
better in your situation. If her behavior is more common than alternatives,
then it is likely to be adaptive because learning increases the frequency of
adaptive behaviors. An evolved cultural learning psychology that incor-
porates such biases increases the chance of acquiring beneficial beliefs
and behaviors. However, these same biases can sometimes lead to the
spread of maladaptive beliefs and practices. For example, the tendency
to imitate the prestigious, or those making credibility-enhancing displays
of commitment, can lead to a “runaway” process analogous to sexual
selection (Richerson and Boyd, 2005), and this may explain the cultural
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evolution of maladaptive cultural systems in which people risk life and
limb to summit icy peaks or achieve spiritual perfection in celibate seclu -
sion (Henrich, 2009).
Culture Is Part of Human Biology and Has Profoundly Shaped
Human Evolution
We have recounted two contrasting accounts of the nature and origins
of human uniqueness. On the one hand, there is a widespread view that
people are like other mammals, just a lot smarter—in essence, we are
brainy, hairless chimpanzees. We have a uniquely flexible cognitive system
that lets us make causal inferences in a wide range of environments and
use that information to create much better tools, and these differences have
allowed us to spread across the world, dominating the world’s biota like
no other creature. By contrast, we argue that individuals are not nearly
smart enough to solve the myriad adaptive problems they face in any of
their many habitats. Even experts lack a detailed causal understanding of
the tools and techniques that permit them to survive. High-fidelity cultural
learning allows human populations to solve these problems because it
allows selective learning and the accumulation of small improvements
over time. Of course, sophisticated, flexible cognition is important too.
However, the degree of cognitive flexibility varies widely in nature—
chimpanzees can solve problems that baffle monkeys, and monkeys are
geniuses compared with opossums. Nonetheless, no species occupies
as wide a range of habitats as Homo sapiens. In contrast, there is a sharp
break between human cultural learning capacities and those of even our
closest relatives. As a result, it is more apt to think of humans occupying
a cultural niche than a cognitive niche.
The evolution of the psychological capacities that give rise to cumula-
tive cultural evolution is one of the key events in our evolutionary his-
tory. The availability of large amounts of valuable cultural information
would have favored the evolution of bigger brains equipped to acquire,
store, organize, and retrieve cultural information, a fact that may explain
the rapid increase in human encephalization over the last 500,000 years
and the evolution of specialized cognitive abilities that emerge early in
life, such as theory of mind, selective social referencing (Stenberg, 2009),
overimitation (Lyons et al., 2007), a functional understanding of artifacts
(Wohlgelernter et al., 2010), and the use of taxonomic inheritance and
category-based induction for living kinds (Atran and Medin, 2008). The
presence of culturally evolved techniques and products—such as fire,
cooking, weapons, and tools—created new selection pressures acting on
our bones, muscles, teeth, and guts (Richerson et al., 2010).
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Culture has opened up a vast range of evolutionary vistas not avail -
able to noncultural species. Nonetheless, culture is as much a part of
human biology as our peculiar pelvis. This approach contrasts with the
common view that culture and biology are in a tug-of-war for control
of human behavior. This common view probably taps into a deep vein
of Western thought, which itself may be the result of evolved cognitive
biases (Bloom, 2004), but it makes little sense. The ancestral condition in
the human lineage is a psychology that does not permit cumulative cul -
tural evolution. Despite earnest efforts, chimpanzees cannot be socialized
to become humans and have little or no cumulative cultural evolution.
Beginning early in human ontogeny, our psychology allows us to learn
from others, powerfully and unconsciously motivates us to do so, and
shapes the kind of traits that evolve. So it does not make sense to ask, does
culture overcome biology? The right question to ask is, how do genetic and
cultural inheritance interact to produce the observed patterns of human
psychology and behavior (Henrich et al., 2010b)?
ACKNOWLEDGMENTS
We thank Clark Barrett for very useful comments on a previous draft
of this article, and two anonymous referees for their help. This work was
supported in part by National Institutes of Health Grant RC1TW008631-02
(to R.B.) and the Canadian Institute for Advanced Research (J.H.).
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