Human Biological and Psychological Diversity
Published online: 17 January 2017
#Springer International Publishing 2017
Abstract Many evolutionary psychologists have asserted
that there is a panhuman nature, a species typical psycholog-
ical structure that is invariant across human populations.
Although many social scientists dispute the basic assumptions
of evolutionary psychology, they seem widely to agree with
this hypothesis. Psychological differences among human pop-
ulations (demes, ethnic groups, races) are almost always at-
tributed to cultural and sociological forces in the relevant lit-
eratures. However, there are strong reasons to suspect that the
hypothesis of a panhuman nature is incorrect. Humans migrat-
ed out of Africa at least 50,000 years ago and occupied many
different ecological and climatological niches. Because of
this, they evolved slightly different anatomical and physiolog-
ical traits. For example, Tibetans evolved various traits that
help them cope with the rigors of altitude; similarly, the Inuit
evolved various traits that help them cope with the challenges
of a very cold environment. It is likely that humans also
evolved slightly different psychological traits as a response
to different selection pressures in different environments and
niches. One possible example is the high intelligence of the
Ashkenazi Jewish people. Frank discussions of such differ-
ences among human groups have provoked strong ethical
concerns in the past. We understand those ethical concerns
and believe that it is important to address them. However,
we also believe that the benefits of discussing possible human
population differences outweigh the costs.
Keywords Differences .Diversity .Evolution .Genetics .
Populations .Psychology .Race
The Arctic is a horrifically cold, often bleak, and an almost
perpetually snow-covered region of the globe with long, dark
winters and brief summers. During those long winters, tem-
peratures often range between −40 and 0 °F. And yet, the
Arctic is not a desolate desert of snow. Roughly 400,000 na-
tive peoples inhabit the region and have been there since well
before the invention of space heaters or electric underwear.
How do these people meet the exigencies of survival in such
a cold, inhospitable environment?
The answer is a combination of cultural and biological
adaptations. The Inuit, for example, have developed a sophis-
ticated array of tools and weapons to facilitate survival in their
harsh environment (Kelly 2013). They have learned effective
ways of hunting and fishing calorie-dense animals such as
seals and whales. Cultural transmission alone, however, is
not responsible for the Inuit’sremarkablecapacitytothrive
in the Arctic. They also have various physiological (and per-
haps even psychological) adaptations that allow them to func-
tion in the cold, including fat insulation of vital organs, bodies
with a high volume to surface area ratio, and a high basal
metabolic rate which produces more body heat than other
Psychology Department, Florida State University, 1107 West Call
Street, Tallahassee, FL 32301, USA
Psychology Department, Carroll College, 1601 N Benton Ave,
Helena, MT 59625, USA
School of Social Work, Department of Epidemiology, Saint Louis
University, One Grand Blvd, Saint Louis, MO 63103-2097, USA
Evolutionary Psychological Science (2017) 3:159–180
population groups with lower basal metabolic rates
(Fumagalli et al. 2015). In the relatively brief period (in evo-
lutionary time) of roughly 30,000 years,certain populations of
Homo sapiens in Northern Eurasia evolved physiological dif-
ferences—perhaps best thought of as differing calibrations on
existing adaptations—to the cold, which continued in the pop-
ulations that entered and inhabited the Arctic (Oppenheimer
2012). The Inuit are not unique. Around the globe, a variety of
human populations have thrived in disparate, often extreme
climates because of both cultural ingenuity and biological
adaptations (Lachance and Tishkoff 2013).
The contention that human populations possess slightly
different phenotypic characteristics because of recent evolu-
tionary pressures is not controversial. Mainstream textbooks,
for example, document many instances of human biological
diversity (Mielke et al. 2011;Molnar2006). Despite this, the
basics of human biologicaldiversity are not integrated into the
social sciences. Furthermore, a straightforward corollary hy-
pothesis has remained largely unexplored in mainstream liter-
ature: that human populations also possess slightly different
evolved psychological tendencies—or more specifically, cali-
brations on existing psychological hardware (Jensen 1998;
Wade 2014). Even a standard evolutionary psychology para-
digm (SEPP), a psychological research program that applies
the principles of natural and sexual selection to human psy-
chology, has asserted that there is a panhuman psychological
nature, and that any nonsex-linked deviations from psychical
unity among humans were likely caused by stochastic pro-
cesses or pleiotropic genetic effects (Tooby and Cosmides
1990; Cosmides et al. 2003; for divergent views, see
Cochran and Harpending 2009).
In this article, we make the case that there is rich human
biodiversity in both morphological and psychological traits,
which is a straightforward result of standard Darwinian pro-
cesses acting on human populations in a wide variety of envi-
ronments. Although the hypothesis that human populations
possess slightly different evolved psychological traits is con-
troversial, we contend that it is an important fact about human
psychology and should not be avoided because of ethical dis-
comfort or political sensitivities (Winegard and Winegard
2014). In fact, we think that the study of human psychological
differences can promote respect and appreciation of ethnic
diversity (Crow 2002). Of course, concerns about the potential
political misuse of research about human diversity is under-
standable and reasonable (Kevles 1998). We hope that this
article will encourage much needed discussion about both
human differences and the moral responsibility of scientists
who study it.
First, we will discuss the rate at which natural selection can
create variations in animals. Common understandings aside,
we will argue that natural selection can provoke change in
existing adaptations quite rapidly. Then we will relate the dis-
cussion about the rate of evolution by natural selection to
humans. We will argue that because modern humans migrated
out of Africa at least 50,000 years ago and spread to different
ecological and climatological niches, they evolved slightly
different anatomical and physiological traits. We will further
argue that they also evolved slightly different psychological
traits and propensities (Frost 2011). Therefore, we will con-
tend that the standard evolutionary psychology paradigm is
incomplete and we will propose a different Darwinian para-
digm and lay out its basic principles. Last, we will end by
discussing the moral dilemmas that arise when studying and
discussing human biological diversity.
Before discussing human evolution and biological diversity,
we will briefly discuss the SEPP, focusing specifically on its
failure to appreciate adequately the breadth of human varia-
tion. After, we will examine rapid evolution, forwarding sev-
eral examples of dramatic evolutionary change among nonhu-
man animals in very brief time spans. This will set up our
discussion of human evolution and biological diversity.
The Standard Evolutionary Psychology Paradigm
and Human Evolution
It is important to be clear that although there is no official
statement documenting what we have called the SEPP, there
does seem to be a reasonable consensus in the literature about
the basic tenets of evolutionary psychology (Barkow et al.
1995; Bolhuis et al. 2011;Buller2005; Laland and Brown
2011). Our description of the SEPP is derived from this liter-
ature but is vulnerable to complaints about oversimplification.
There is, of course, substantial variation within evolutionary
psychology (see, e.g., Swami 2011). Our point in covering the
SEPP is not to assail what has become a foundational field of
psychology. Rather, our intention is to criticize a common
view of human evolution, which, we believe, is erroneous.
The SEPP arose in the late 1980s, and early 1990s, a result
of the synthesis of the cognitive revolution in psychology and
the “selfish gene”(or gene-centric) revolution in biology
(Dawkins 1976; Pinker 1997; Plotkin 2004). According to
the SEPP, human brains/minds are evolved physical systems
that consist of myriad modules, or largely encapsulated pro-
cessing systems that are designed to solve evolutionarily rel-
evant and recurrent problems (Barkow et al. 1995). Human
brains largely evolved in the Pleistocene, and therefore, hu-
man mental adaptations evolved to solve problems faced by
distant hunter-gatherer ancestors in Africa (Buss 1995).
Because evolution is a slow process, the human brain has
changed only trivially since H. sapiens left the African conti-
nent some 100,000 years ago.
160 Evolutionary Psychological Science (2017) 3:159–180
The two most important tenets of SEPP which we believe
should be slightly modified are as follows (see also Bolhuis
et al. 2011, box 1):
1. Gradualism. As we mentioned, the working assumption
of the SEPP is that the human mind is comprised of com-
plicated programs that were designed to solve recurrent
evolutionary problems. Such programs require many hun-
dreds of generations to evolve because natural selection is
slow; therefore, human skulls house “stone age”minds—
minds that have not been “updated”to “post-hunter gath-
erer conditions”(Tooby and Cosmides 2005,p.57).We
should be clear at this point and note that we are not
suggesting that gradualism is, by definition, an incorrect
assumption. Indeed, it has been, and should remain, a
prevailing assumption among evolutionists. Rather, what
we would challenge is the assumption—present in some,
but not all corners of evolutionary psychology—that nat-
ural selection is precluded from working more rapidly
than was previously assumed in the field of evolutionary
2. Panhuman Nature. The SEPP asserts that there is a uni-
versal human nature. This is a relatively straightforward
consequence of gradualism, and in principle, we do not
dispute it. Because evolution is a slow process, the SEPP
reasoning continues, the human mind is adapted to life on
the African continent, and all humans possess a universal
mental architecture that has not changed in hundreds of
thousands of years. Although humans did eventually
leave Africa and spread across the globe, colonizing dra-
matically disparate environments, they have not inhabited
those environments long enough to develop anything oth-
er than superficial differences from each other. The recal-
ibration we propose in the pages to come for the concept
of a panhuman nature is not that we should reject the
notion of human psychological universals. Rather, we will
argue that the panhuman nature possessed by our species
has been differentially adjusted depending on local and
regional selection pressures encountered by migrating hu-
man groups (see also, Cochran and Harpending 2009).
The SEPP view of the pace of evolution is shared by many
(though, not all) scholars. The Public Broadcasting Station’s
(PBS) online companion to its critically lauded series on evo-
lution noted that, “for many species, the process (evolution by
natural selection) operates so slowly that it is not observable,
except over thousands or hundreds of thousands of years…”
Professors of biology often emphasize how plodding of a
process natural selection is when constructing new adaptations,
noting that one of the challenges to understanding it is that it
requires one to imagine almost unfathomable stretches of time
(Dawkins 1997). In many very important respects, it is true that
evolution is slow (or more specifically, the construction of de
novo and complex adaptations requires ecological time). Life is
roughly four billion years old. Multicellular organisms are ap-
proximately 600 million years old. Mammals are some 300
million years old (Fortey 1999). The last common ancestor
shared between humans and chimpanzees is roughly six million
years old (Brunet et al. 2002). These are vast time scales and
suggest that evolutionary change is so slow that it is difficult to
understand using everyday time scales. It takes a very, very long
time to arrive at a black bear from an echidna. Furthermore,
there often are long periods of relative evolutionary stasis in
which there is little evolutionary change (Dawkins 1986;see
also Gould and Eldredge 1977).
Dramatic evolutionary change, however, can occur rela-
tively rapidly; and less dramatic change, even more rapidly.
Since at least the 1960s, scholars have documented sundry
examples of such rapid evolution, sometimes occurring in as
little as a few generations (Carroll et al. 2007). These studies
demonstrate that changes in ecological and climatic condi-
tions can induce rapid evolutionary alterations of phenotypes,
though not necessarily resulting in brand new complex adap-
tations. Below, we will document three examples of rapid
evolution, sometimes called “evolution in ecological time”
(Palumbi 2002). These examples are germane to human evo-
lution, which we will discuss in the next section, because they
illustrate that novel ecological and climatic conditions, such as
humans would have faced when migrating out of Africa, can
spur rapid bursts of evolutionary change.
Italian Wall Lizards
In 1971, researchers transported five adult pairs of Italian wall
lizards (Podarcis sicula) from the Croatian island of Pod
Kopište to the island of Pod Mrčaru, which is roughly four
and a half kilometers to the east in the Adriatic sea (Herrel
et al. 2008). The islands are quite similar in elevation and
terrain; however, most likely because of a larger population
of sheep, the vegetation on Pod Kopište is shorter and less
thick, possibly providing less shelter from aerial predators.
The lizards were then allowed to live and reproduce naturally
until researchers returned to examine them in the 2000s (after
roughly 30 generations).
Researchers found remarkable differences between the two
populations. The lizards on Pod Mrčaru, for example, are larger
and have shorter hind limbs than those on Pod Kopište. Because
of their shorter hind limbs, the lizards also have a slower maxi-
mum sprint speed and fatigue faster than the Pod Kopište lizards
(Vervustetal.2007). The Mrčaru lizards also exhibit an attenuated
response to predators. The researchers speculated that the thicker
protective brush on Pod Mrčaru caused these changes. More
Evolutionary Psychological Science (2017) 3:159–180 161
specifically, the brush likely provided more safety from birds and
thus eased selective pressures to maintain hypervigilant antipred-
Researchers found other morphological differences between
the populations. The head length, width, and height of the Pod
Mrčaru lizards are larger than the Pod Kopište lizards; conse-
quently, their bite force is stronger. Perhaps most remarkably,
the lizards on Pod Mrčaru possess what appears to be an entirely
new morphological trait (one shared with other, unrelated lizards
that consume largely plant-based diets): a cecal valve—amuscle
that separates the large and small intestines (Herrel et al. 2008).
The valve slows down food movement and ultimately allows for
the digestion of cellulose (Herrel et al. 2008). These changes
may have been impelled by a shift to a more plant-based diet in
the Mrčaru lizards than the ancestral population. The stronger
bite force of the Mrčaru lizards probably allows them to con-
sume smaller pieces of plants, which aids in the digestion of
difficult to break down plant matter. And the cecal valve, noted
above, further facilitates plant digestion.
As a final point, it is imperative to consider the possibility
that factors other than natural selection can explain the
morphological and behavioral changes observed in the
lizards. Herrel et al. (2008, p. 4794) make this point explicit,
in fact: “Moreover, our data show not only rapid, directional
changes in quantitative phenotypic traits related to the inclu-
sion of plant matter into the diet, but also the evolution of
novel morphological structures on extremely short time
scales. Although the presence of cecal valves and large heads
in hatchlings and juveniles suggests a genetic basis for these
differences, further studies investigating the potential role of
phenotypic plasticity and/or maternal effects in the divergence
between populations are needed.”In other words, when dif-
ferences across groups emerge, the default assumption should
not necessarily be that natural selection is responsible for
shaping the divergences. Rather, that issue must be investigat-
Cane Toads and Snakes
In 1935, cane toads (Bufo marinus) were introduced to
Australia to eradicate pests that were damaging northeastern
Queensland cane fields. The cane toad is a large and extremely
poisonous toad with a unique cardiotoxin (Bufadienolides)
(Shine 2010). Australia has no native toads; therefore, the
cane toad presented a novel, poisonous prey item to many
naive predators, including many species of snake (Phillips
and Shine 2004,2006). Since the early 2000s, researchers
have documented intriguing instances of rapid evolution in
several of these vulnerable snakes (in fewer than 23 snake
Red-bellied black snakes (Pseudechis porphyriacus), for
example, that inhabited areas exposed to cane toads evinced
greater resistance to bufotoxin and decreased preference for
the toad as prey relative to red-bellied black snakes not ex-
posed (ecologically) to cane toads (i.e., tweaks on existing
adaptations) (Phillips and Shine 2006). Researchers used lab-
oratory studies to demonstrate that these changes were prob-
ably not the result of learning or of repeated exposure to
bufotoxins, but were likely the result of adaptive evolutionary
change. Researchers also found that several species of snakes
(P. porphyriacus and Dendrelaphis punctulatus)thatwereex-
posed to toad-inhabited areas developed larger bodies and
smaller relative head sizes than species not exposed to toad-
inhabited areas. These adaptations appear to protect the snakes
from eating large toads with fatal doses of toxin (Phillips and
Yet, as we mentioned above, caution is appropriate when
interpreting these findings. Regarding the possible alternative
explanations to their results, Phillips and Shine (2004,p.
17154) point out that: “Although we have no direct data to
distinguish between these two scenarios (selection versus
plasticity), our data argue against an indirect environmental
effect.”Having considered the limitations of their study, the
authors do contend (Phillips and Shine 2004, p. 17154):
“Therefore, the morphological changes must be a conse-
quence of (and probably also a response to) selection against
small bodies and large heads.”, yet they also carefully explain
additional caveats and assumptions that are important to keep
in mind when making such an argument (e.g., trait heritability,
further response to selection, etc.). The larger point, however,
is that the same type of careful inference will be required as
scholars investigate similar types of research questions in hu-
As a last example, the house sparrow (Passer domesticus)was
introduced to North America in the 1850s and quickly spread
throughout the continent. In the 1960s, Johnston and Selander
(1964) began to examine geographical variation in the
It is possible that some rapid evolutionary change and/or divergence across
population groups are caused by epigenetic effects rather than through the
processes of natural and sexual selection (Riddihough and Zahn 2010).
Epigenetics is, unfortunately, unclearly defined in much of the literature, but
generally refers to information transmitted during cell division “other than the
DNA sequence per se”(Feinberg and Fallin 2015,p.1129;seealsoPtashne
2013 for additional clarification regarding epigenetics). Many social scientists
who use the term “epigenetics”are referring to transgenerational epigenetic
effects that are induced by the external (and in particular, social) environment,
and then passed transgenerationally from parent to offspring (Dickins and
Rahman 2012; Moffitt and Beckley 2015). If such epigenetic effects are com-
mon, it is possible that two populations would diverge without genetic differ-
entiation. This is an important area offuture research and is currently the topic
of much research, hyperbole, and debate (see, e.g., Moffitt and Beckley 2015;
Ptashne 2013). We hold the possibility of epigenetic effects accounting for
some population differences and some instances of rapid evolution as an open
hypothesis. However, we note that the best evidence to date suggests that most
epigenetic effectsdo not survive beyond the lifetime of an individual (i.e., they
are not transgenerational) (Radford et al. 2014).
162 Evolutionary Psychological Science (2017) 3:159–180
sparrow, documenting a wide variety of differences plausibly
related to environmental and climatic diversity. For example,
birds in northern environments were larger than birds in south-
ern environments, probably because larger bodies are better
able to cope with the rigors of cold winters (Johnston and
Selander 1971). They also found differences in the amount
of sexual dimorphism across the continent, also plausibly re-
lated to survivability in harsh winter conditions and storms
(large male birds survived better than small; medium-sized
female birds survived better than large or small) (Johnston
and Selander 1973). Speaking of the regional variation of
the house sparrow, Johnston and Selander (1964) asserted,
“Racial differentiation [sic] of house sparrow populations
may require no more than 50 years”(p. 548).
Summary and Consequences
As these examples illustrate, evolution by natural selection
can create adaptive changes quite rapidly. In some species,
these changes occurred in fewer than 20 generations (roughly
the equivalent of 400 years for humans). Regional variation in
North American birds is an excellent example of the power of
climatic selective pressures and demonstrates the remarkable
capacity of Darwinian processes to shape and tune the traits of
animals. Of course, none of these examples illustrate complete
morphological transformations. The path from the first reptiles
to the first mammals, for example, was very long and winding
(Dawkins 2005). But neither were the changes in these exam-
ples completely superficial or uninteresting to a biologist or
ethologist (a general error common in previous SEPP
Consider the Italian wall lizard from the first example.
There is, from one perspective, a “pan-lizard”design and be-
havioral repertoire. Wall lizards on one island do not have
entirely new behavioral patterns, do not, for example, hunt
sleeping birds at night. However, the lizards on Pod Mrčaru
do have some measurably different behavioral propensities
from the lizards on Pod Kopište. If one is interested in general
lizard behavioral repertoires, then it makes sense to speak of a
universal Italian wall lizard nature. If, however, one is inter-
ested in the subtleties of antipredator behavioral responses,
then perhaps it makes sense to speak of a differentially cali-
brated Italian wall lizard nature (for additional discussion and
examples, see also Wada-Katsumata et al. (2013)) (see
In the next section, we will cover the basics of recent human
migrations and evolution, noting that the same principles that
apply to the animals we discussed above also apply to
humans. We will forward several (nonpsychological)
examples of regional human adaptive evolution. These exam-
ples will build the case that there are, indeed, evolutionary
differences among human populations and pave the way for
a further exploration of psychological differences among hu-
Anatomically, modern humans first evolved in east Africa
between 200,000 and 100,000 years ago (Stringer 2012).
According to some researchers, these humans were not yet
cognitively modern, lacking the symbolic capacities that dis-
tinguished later humans. Klein (2009), for example, argues
that humans did not cross the symbolic Rubicon until roughly
50,000 years ago. Others dispute Klein’s assertion, believing
that the concept of cognitive or behavioral modernity is anti-
quated, and should be eschewed (Shea 2011). Whatever the
truth, the basic story is that H. sapiens evolved in east Africa
around 150,000 years ago and that the archaeological record
suggests an efflorescence of symbolic culture some
50,000 years ago (Klein 2009).
At some point after 150,000 years ago, humans began to
migrate out of Africa. The details of these migrations are also
disputed, but the basic outline is relatively uncontroversial.
Sometime after 150,000 years ago, humans spread into the
Near East and by about 45,000 years ago, humans had spread
across much of Asia, Western Europe, Australia, and Oceania,
and by roughly 15,000 years ago, they had traversed a land
bridge into North America (Carto et al. 2009; Klein 2008,
2009; Stringer 2000). Some researchers contend that there
were two or more waves of migrations out of Africa, with
one group taking a southern route to Asia and another taking
a more northerly route into Northern Eurasia and eventually
into Western Europe (Reyes-Centeno et al. 2014). Others con-
tend that there was one migration out of Africa that eventually
populated the rest of the inhabited globe (Posth et al. 2016).
Those who argue that there were two (or more) migrations
tend to push the date of the first migration back further
(∼120,000 years ago) than those who contend there was just
one (∼60–50,000 years ago).
Whatever the granular details of the human exodus from
Africa, the picture is clear enough for purposes of exploring
human biological diversity. By 45,000 years ago, many hu-
man populations were reproductively isolated (by distance or
by geographical obstacles such as water or mountains) from
each other. And they were facing dramatically different selec-
tive regimes because they occupied radically different ecolog-
ical and climatic regions of the globe (Brown 2009). In much
of Europe, for example, humans encountered seasonal weath-
er patterns, lush growing seasons punctuated by bleak and
barren winters. In much of Africa, on the other hand, the
weather was generally hotter and more fruitful, and the win-
ters were much more moderate than in Europe. In fact, during
Evolutionary Psychological Science (2017) 3:159–180 163
Tab l e 1 Examples of rapid evolution in nonhuman animals
Organism Trait(s) (altered) Function References
Soapberry bug (Leptocoris
Beak length (increased) Extract seeds from balloon vine Carroll et al. (2005)
Carolina anole (Anolis
Toepads (larger size) + lamella (greater number) Ability to occupy higher ground due to invasion
from Cuban brown lizard
Stuart et al. (2014)
Increase in body size + decrease in relative head size +
increased resistance to toxin + decreased preference
for cane toads as prey
Resistance to cane toad poison Phillips and Shine (2004,2006)
Green tree snake
Increase in body size + decrease in relative head size Resistance to cane toad poison Phillips and Shine (2004)
Italian wall lizard (Podarcis sicula) Increased size + decreased limb size + attenuated
predator response + increased head size + increased
bite strength + cecal valve
Adaptations to new island with few predators and
exploitation of feeding niche involving high
levels of plant matter
Herrel et al. (2008),Vervustetal.(2007)
House sparrow (Passer
Morphological and color variation Adaptation to climatic diversity Johnston and Selander (1964,1971,1973)
North American red squirrel
Earlier seasonal breeding time Adaptation to warming spring temperature.
Allows squirrel to hoard more pinecones
Réale et al. (2003)
Domestic cat (Felis silvestris
Human tolerance + tameness Adaptation to human hosts allowed cat access to
food supply (mice)
Driscoll et al. (2009)
Pygmy grasshopper (Tetr i x
Melanism Adaptive selection in response to the need to be
camouflaged in recently burned environments
Forsman et al. (2011), Karpestam et al.
kdr mutation allowing pyrethroid insecticide resistance Ability to survive in agricultural locations with heavy
Yawson et al. (2004)
(Diabrotica virgifera virgifera)
Partial resistance to Cry3Bb1 maize (Bt maize) Ability to eat transgenic Bt corn crops Gassmann et al. (2011)
Morphological variation + increase in gill surface area Response to Nile perch predation and low oxygen
van Rijssel and Witte (2013), Witte et al.
Alewife (Alosa pseudoharengus) Decrease in gill-raker spacing Response to decline in large-bodied zooplankton
species to feed upon
Palkovacs et al. (2014)
Ground finch (Geospiza fortis) Increase in bill depth + bill length + bill width + body
Response to drought and lack of small seeds to feed upon Boag and Grant (1981), Weiner (1995)
Peppered moth (Biston betularia) Melanism Adaptive selection in response to darkened trees (from
Cook et al. (2012)
Trinidadian guppy (Poecilia
Life-history variation Adaptive selection in response to different predators Reznick and Endler (1982)
164 Evolutionary Psychological Science (2017) 3:159–180
the last glacial maximum (∼20,000 years ago), humans in
much of Europe were driven into various refugia because
much of the continent was cold, dry, and covered by ice
(Gamble et al. 2004; Stewart and Stringer 2012). Some re-
searchers contend that the cold, fluctuating European climate
was the primary cause of the extinction of the Neanderthals
Humans, like many animals, actively alter their environ-
ment, which changes the selection pressures they face
(Laland et al. 2001; Laland and Sterelny 2006). In fact,
humans may be the paradigmatic example of a niche-
creating species, using brains rather than brawn to conquer
the world (Baumeister 2005;Pinker2010). Across the globe,
humans devised distinctive cultural systems to cope with their
environments, creating vastly different selective regimes from
one culture to another. For example, agriculture first arose in
the Levant some 11,000 years ago and eventually spread
across Western Eurasia (or was transmitted by conquering
migrants) (Bellwood 2004). It also arose independently at dif-
ferent times in East Asia, Africa, and the Americas (Diamond
and Bellwood 2003). Agriculture radically changed the way
humans interacted with their environments, allowing them
purposefully to grow several nutrient-rich crops, increasing
sedentism and leading, when coupled with animal domestica-
tion, to the development of the first civilizations. The selective
pressures faced by an agriculturalist are different from those
faced by a hunter-gatherer—just as the selective pressures
faced by a Northern European are different from those faced
by a Southern African. The selective pressures faced by agri-
culturalists led to various adaptations that are less prevalent in
populations without a history of agriculture (i.e., lifetime lac-
tose tolerance; see Cochran and Harpending 2009). There are,
in fact, myriad examples of human adaptations to specific
climatic, ecological, and cultural conditions in the literature.
One of the most pronounced differences among human pop-
ulations is the color of their skin. The average Danish person,
for example, tends to have skin that is quite fair, the average
Egyptian has skin that is olive, and the average Sub-Saharan
African has skin that is quite dark (Jablonski 2014; Beall et al.
2010). Many researchers have suggested that skin color is
adaptively tuned to ultraviolet radiation exposure and intensity
(Jablonski 2004; Relethford 1997). Dark skin provides protec-
tion from potentially damaging ultraviolet radiation and be-
came necessary after the near complete loss of hair on the
human body. Excessive ultraviolet radiation penetration can
cause deleterious mutations, leading to cancer, and it can also
damage folate, leading to folate deficiencies (Greaves 2014;
Jablonski and Chaplin 2010). Evidence supports these
For example, Jablonski and Chaplin (2000) found robust
correlations between ultraviolet radiation intensity and skin
coloration, with dark, protective skin coloring found in areas
exposed to concentrated ultraviolet radiation. A series of trag-
ic natural experiments in Africa also provide support. One in
every few thousand Africans is afflicted with a condition
called albinism. Albinos have much lighter skin, eyes, and
hair than the average person in the population. Okoro
(1975), in a study of 1000 Nigerian albinos, found that many
of them had potentially malignant skin cancers. Kromberg
et al. (1989) found similarly elevated rates of skin cancer in
albinos from South Africa. Greaves (2014) argues that this
evidence supports the hypothesis that hominins developed
dark skin to protect from potential ultraviolet radiation-
induced cancers (but see Hong et al. 2006).
In areas exposed to less intense ultraviolet radiation, a dif-
ferent adaptive problem arose: the need to absorb enough
sunlight to trigger pre-vitamin D
synthesis. Many researchers
contend that this problem led to increasingly lighter skin in
areas with less intense ultraviolet radiation (Greaves 2014).
Some scholars argue that this explains why women have ligh-
ter skin than men in almost all known populations: Women
need more vitamin D
because of the physiological rigors of
pregnancy and lactation (Jablonski and Chaplin 2000).
Others, however, contend that lighter skin may have been
sexually selected in populations that were not constrained by
intense ultraviolet radiation (Diamond 1994; Frost 2007). See
also Darwin (1871) for a broader discussion of race and sexual
selection. Either way, there is consensus that human popula-
tion variation in skin color was impelled by the forces of
natural (and sexual) selection and that the most conspicuous
example of human biological diversity is not a side effect of
genetic drift or other nonadaptive processes.
Another intriguing but less conspicuous example of human
biological diversity is lactose tolerance/intolerance. Some hu-
man populations are able to digest milk into adulthood, where-
as others are not able to. The nutrient-rich sugar in milk is
lactose, which cannot be digested without the enzyme lactase.
In most mammals, the production of lactase dramatically
slows at an early age because they do not consume milk after
weaning (Swallow 2003). Thirty-five percent of the current
human population, however, is able to digest lactose into
adulthood (Cochran and Harpending 2009).
Scholars contend that lactose tolerance is a remarkable ex-
ample of gene-culture coevolution (Gerbault et al. 2011). In
areas where agriculture and animal domestication was preva-
lent, humans had probably discovered ways of reducing the
lactose levels of milk by fermenting it (Curry 2013). This
allowed them to consume it as cheese or yogurt. But at some
point, a mutation arose that allowed adults to digest lactose
Evolutionary Psychological Science (2017) 3:159–180 165
(by continuing the production of lactase into adulthood), pro-
viding a new source of calories and a major fitness advantage.
Geneticists estimated that humans who possessed this muta-
tion might have produced up to 19% more offspring than
those who lacked it (Bersaglieri et al. 2004). This mutation
probably first emerged between the Balkans and Central
Europe around 7500 years ago (Itan et al. 2009). Different
mutations, which allowed adults to digest lactose, also arose
among other populations across the globe (e.g., the Dinka in
Southern Sudan and Maasai in Kenya and northern Tanzania)
(Check 2006; Tishkoff et al. 2007). In this case of human
biological diversity, the human capacity to alter ecological
niches led to novel selective pressures and the spread of sev-
eral genetic mutations that allowed them to survive better in an
environment with milk-producing domesticates.
As a last example of human biological diversity, consider the
capacity of certain human populations, such as Tibetans, to
survive the rigors of high-altitude environments. Oxygen is
abundant near sea level but becomes less abundant as the air
thins at higher altitudes. At 2500 m (8,50 ft) above sea level,
the stresses of reduced oxygen levels become acute for
humans, triggering a concatenation of physiological re-
sponses. At 4000 m (13,200 ft) above sea level, they become
potentially fatal. For example, 2–6% of people exposed to
altitudes over 4000 m develop a potentially mortal suite of
symptoms known as high-altitude pulmonary edema
(HAPE). One to 2% develop high-altitude cerebral edema
(Beall et al. 2012). And yet, the Tibetan plateau, which is
roughly 4500 m above sea level, is not empty. Some
600,000 people live on the plateau at altitudes exceeding
4500 m (Wu 2001).
Because they have inhabited such extreme altitudes for
thousands of years, the Tibetans on the plateau possess unique
high-altitude adaptations. For example, Tibetans have larger
chest circumferences and greater lung capacity than Han
Chinese peoples who live at lower altitudes in nearby regions
(Gilbert-Kawai et al. 2014). Tibetans also breath at faster rates
than other human populations, which, when coupled with
their increased lung capacity, allows them to inhale large
amounts of air to compensate for the reduced oxygen levels
(Beall 2007). In addition, Tibetans appear to have greater
blood flow than lower dwelling peoples, probably caused by
a great number of vasodilators compared to vasoconstrictors
than in other human populations (Beall et al. 2012).
Researchers have isolated several potential genes that may
be responsible for these adaptations, suggesting that the
Tibetans’unique physiological profile is at least partially a
product of recent natural selection (Bigham and Lee 2014;
Simonson et al. 2010;Wangetal.2011).
These examples, and many others, suggest that human pop-
ulations have evolved unique physiological and anatomical
profiles because of different selective pressures in disparate
ecological, environmental, and climatic niches. Some of these
changes, such as lactose tolerance, were impelled by cultural
innovations; others, such as skin pigmentation, were com-
pelled by climatic variation. But whatever the causes, it seems
reasonable to suggest that there is some meaningful physio-
logical variation among human population groups. Are there
human races, though?
Race and Human Populations
Before proceeding with our discussion of human biological
diversity, we want to discuss briefly the controversial concept
of race. Thus far, we have not used the term for several rea-
sons. Primarily, we have avoided it because it is a loaded and
contentious concept, associated with a long history of preju-
dice and discrimination. Perhaps because of this regrettable
legacy, the concept has impelled copious, often vitriolic dis-
cussion. Some philosophers and scientists have argued that
race, as traditionally conceived, does not really exist (Kaplan
and Winther 2013). It is, they contend, more of a social con-
struct than a biological reality, a fiction foisted on the world to
justify a system of racial oppression (Graves 2003). Other
philosophers and scientists, however, have argued that races
do exist and that the concept is as legitimate as any other fuzzy
concept in biology such as cline or species (Sesardic 2010). To
a large degree, the debate about race boils down to definitions
(Shiao et al. 2012;Spencer2014). One can always repudiate a
particular definition of race and therefore deny that races exist.
Here, we will accept a moderate position: metaphysics
aside, race is a useful concept; however, races are not immu-
table types, but fuzzy categories that can change depending on
the level of analysis one chooses. Perhaps a usefulcomparison
can be made between the construct of race and the construct of
film category. Films are often categorized into horror, drama,
comedy, and romance. These categories have some predictive
value. If someone tells you that The Karate Kid is a coming of
age drama, you have reasonable expectations about the kind
of movie it is. Probably, it is not the kind of movie in which an
unstoppable villain slaughters hapless teenage babysitters.
Yet, these categories are not immutable, and they did not de-
scend from a Platonic heaven. What category does Pulp
Fiction fit in? Is it drama? Comedy? Horror? Furthermore,
the usefulness and “reality”of film categories depend upon
one’s own interests. On Netflix, films are often sorted into
remarkably narrow and precise categories such as independent
films with strong female leads. This category is obviously
more specific than comedy or horror, and it is therefore even
more predictive. A movie in this list almost certainly is not
about a team of action heroes who work together to defeat an
166 Evolutionary Psychological Science (2017) 3:159–180
alien and a demigod. And it also almost certainly is not about a
disgruntled male who joins a secret fight club. As these con-
structs become more and more fine grained, they become
more and more predictive, but also less general and
The same basic principles apply to humans. Evidence from
a variety of disciplines, including genetics, anthropology, ar-
chaeology, and paleontology, indicates that human popula-
tions evolved distinctive features after spreading from Africa
and settling in different ecological and climatic niches
(Bellwood 2013; Cavalli-Sforza et al. 1994; Molnar 2006;
Wade 2014). Although such human biological variation is
often ignored by social scientists, it is not really a matter of
dispute among researchers in the relevant disciplines (see
above). And because human populations do vary, they can
be clustered and classified. The construct of race allows re-
searchers to do this. One can begin with broad, continentally
based categories: Caucasians, East Asians, Africans, Native
Americans, and Australian Aborigines (Wade 2014). They are
broad, general categories, but they have some predictive val-
ue. Importantly, there is nothing real in some metaphysical
sense about this categorization. It is simply a pragmatic clas-
sification system that captures some differences in the world
and allows researchers better to make sense of the pattern of
human variation (Wade 2014). One can then move to a more
granular level of categorization, replacing broad continental
racial categories with more localized population categories,
perhaps based on specific genetic signatures (haplotypes).
There are several powerful rebuttals to the contention that race
is a useful construct which we should address before proceed-
ing. One of the most common arguments levied against the
usefulness of race is that human variation is clinal or gradual,
not discrete (Gravlee 2009;Hochman2013). Consider skin
color for a conspicuous example. Human populations exhibit
a continuum of skin colors, not a few discrete categories.
Therefore, it does not make sense to divide humans into dis-
tinct and discrete races. The charge is correct, but the target is
mistaken. We are not familiarwith any empirically compelling
arguments suggesting that human populations are discrete
(see, for example, Sarich and Miele 2005; Sesardic 2013;
Wade 2014). Consider the example of film categories from
above. The categories are certainly useful (which is why cor-
porations use them), but films are not really discrete types.
There is a continuum from comedy to drama (maybe mea-
sured by laughs and tears?), and it is not always clear to which
particular category a film belongs. However, this does not
vitiate the overall usefulness of the categories. The same ap-
plies to race. Variation is often clinal—although some popu-
lation variation is relatively discrete (Risch et al. 2002; Wade
2014). But this does not mean that the categories are useless.
Racial categories are fuzzy and there are often large penum-
bras between one category and another, but they allow re-
searchers to capture and analyze human population variation
(both phenotypically and genotypically) (Pickrell and
Pritchard 2012; Rosenberg et al. 2002).
Another argument forwarded against racial classifica-
tions is that they are arbitrary. Diamond, for example,
argued that “There are many different, equally valid pro-
cedures for defining races, and those different procedures
yield very different classifications”(Diamond 1994,p.
84). He concludes that society (including scientists)
should not codify human differences into arbitrary taxo-
nomic groups. Such an assertion is correct. Racial clas-
sifications are not determined by essences and, therefore,
can reflect the interests of the humans who are using
them (Kaplan and Winther 2013). Some classification
schemes might have three categories and some might
have 10 and some might have 30. Furthermore, the
purpose of the classificatory scheme might change the
classifications. As Diamond (1994) notes, if researchers
are concerned with antimalarial genes, they might devel-
op a different classification scheme than if they are in-
terested in skin pigmentation. However, although racial
categories do not pick out real world essences, they are
not as arbitrary as Diamond and others suggest.
Researchers do not concoct racial categories without
motivation just because, and neither do they do so for
purely political or social reasons. (Of course, social and
political forces may interact in complicated ways with
scientific narratives about reality, but that is a discussion
best left to philosophers and historians of science;
Roediger 2006). They are constrained by reality and by
the commonly accepted principles of scientific classifica-
tion, such as coherence and parsimony. Therefore, re-
searchers generally take into account (1) evolutionary his-
tory or shared ancestry, (2) genetic profiles, and (3) phe-
notypic profiles when creating a classification scheme.
Consider an example. One might suggest that
Scandinavians should be classified with Nilo-Saharan
speaking ethnic groups in East Africa because both have
the ability to digest lactose into adulthood (Check 2006).
But this classificatory scheme would quickly run afoul of
basic parsimony. First, these groups almost certainly di-
verged from each other before developing the ability to
digest lactose into adulthood; second, they did not evolve
on the same continent; third, they do not share other phe-
notypic traits (such as the texture of their hair, as well as
their skin pigmentation); and fourth, their ability to digest
lactose appears to be caused by different genetic mutations
(thus supporting the hypothesis that lactose tolerance is not
a shared derived trait in these populations; Tishkoff et al.
2007). So, although racial categories are pragmatic, they
are not arbitrary human inventions.
Evolutionary Psychological Science (2017) 3:159–180 167
A final argument often forwarded against the use of racial
classifications is that the genetic variation between human pop-
ulations is small and dwarfed by the genetic variation within
populations (Lewontin 1972;Templeton2013). Therefore, so
this argument goes, racial classifications contain almost no
meaningful biological information. There are two counterargu-
ments to this. First, if one focuses on the correlational structure
among multiple genetic loci instead of serially examining single
loci or averaging over multiple loci, then there are clear and
biologically informative differences among human populations
(Cochran and Harpending 2009; Edwards 2003; Tang et al.
2005). In other words, different human population groups are
recognizable by their genetic profiles but only if one examines a
pattern of genetic loci. Tang et al. (2005), for example, reported
evidence that self-reported ethnicity corresponded very closely
with genetic clusters derived from 326 microsatellite markers.
Other studies have found similar power to detect accurately
people’s ancestry (Guo et al. 2014; Moreno-Estrada et al.
2014). Of course, this would be impossible without sufficient
genetic information to distinguish among human populations.
And second, even if there were not yet clear genetic evidence
of differences among human population groups, there is clear
phenotypic evidence. Human populations differ from each other
in many ways, both culturally and biologically,as we documented
in the “Human Evolution”section. Small genetic differences can
lead to noticeable and important (from a scientific point of view)
phenotypic differences. Consider the Italian wall lizards from
above for an example. The Pod Mrčaru lizards had, in a mere 20
generations or so, developed a novel phenotypic trait, a cecal
valve, that distinguished them from their close relatives on Pod
Kopište. Genetic analyses showed that both lizards belong to the
same species and, in fact, are genetically indistinguishable using
mitochondrial DNA (Herrel et al. 2008). Of course, there quite
likely are genetic differences between the Pod Mrčaruand the Pod
Kopište lizards. The differences, however, are difficult to detect
and analyze. It would be silly to suggest that the lizards are not
different simply because researchers cannot, as of now, pinpoint
genetic differences between them. Of course, it is possible that
future research will determine that in fact the physiological chang-
es were not caused by genetic changes, and instead were a product
of developmental plasticity. But, as of now, it is a very plausible
hypothesis that they are the results of genetic changes.
Although racial categories are scientifically defensible and
have been used productively (but also destructively), we pre-
fer to use the term human population. The argument above,
however, is germane whether researchers use the term race,
ethnic group, breeding group, or human population. Any of
these terms is a commitment to a nomenclature that accepts
the reality of human biological diversity and accepts that such
diversity can be classified for analytical purposes.
Evolutionary Differences Among Groups
Thus far, we have introduced what we called the SEPP, and
noted that we were going to recalibrate two of its basic pre-
mises. The first premise was gradualism, which contends that
evolution by natural selection is a very slow phenomenon and
that human populations have not had enough time to evolve
meaningful differences. We argued that this position requires
adjustment because (1) natural selection can differentially
sculpt traits quite rapidly, as documented by many researchers
(see “Background”section), and (2) there is copious evidence
that human populations differ from each other somewhat
physiologically and that natural selection continues to affect
human populations (Hawks et al. 2007;Zuk2013). Adjusting
gradualism in this manner requires that we reconsider the idea
of a panhuman nature. It would be remarkable, as we will
discuss below, if human populations were completely similar
psychologically despite having endured different selective re-
gimes in different environments.
In this section, we will forward one approach to human
diversity, contending that different human populations do in-
deed possess meaningfully different psychological profiles.
We focus on the SEPP, but most social science approaches
to human psychology accept previous conceptions of a pan-
human psychological nature, so this discussion should be rel-
evant to social scientists more broadly.
We will then forward two potential examples of human
psychological diversity. These examples will be speculative,
as we freely confess, because researchers have not focused on
biologically based psychological differences among human
populations. It is important to keep this in mind, because some
of our speculations may turn out false.
Adjustment to Standard Evolutionary Psychology
The SEPP is primarily a science of human universals. Early
proponents were interested in universal mental adaptations
that arose from complex organic substrates (Pinker 1997;
Tooby and Cosmides 1989). And, as noted, many of the early
SEPP researchers did not think there were interesting geneti-
cally based psychological differences among human popula-
tions (Cosmides et al. 2003). This approach to human nature
was and is undeniably powerful and productive. From one
level of analysis, the proposal of a panhuman nature is
accurate and fruitful. Humans share many traits and
tendencies that do not vary from population to population.
Brown (1991) and other anthropologists have documented
myriad human universals. Evolutionary psychologists have
also explicated the mental architecture behind numerous be-
haviors including mating preferences, kin recognition, and the
This is a slightly altered version of an argument that was made by the authors
earlier (Winegard et al. 2016).
168 Evolutionary Psychological Science (2017) 3:159–180
desire for status, to name a few (Buss 1989; Henrich and Gil-
White 2001; Lieberman et al. 2007).
However, as we have argued throughout this paper, there
are many biologically based differences among human popu-
lations. These differences are not the result of dramatic mor-
phological alterations. Humans on one remote island do not
have three arms or two heads. Rather, they are the result of
subtle, correlated changes in various organ structures.
Consider an analogy that might make this clear while simul-
taneously illuminating the explanatory importance of popula-
tion differences. Most cars are designed from the same basic
blueprint and consist of similar parts—an internal combustion
engine, a gas tank, a chassis, tires, bearings, spark plugs, et
cetera. Carsas distinct as a Honda Civic and a Subaru Outback
are built from the same basic blueprint and comprised of the
same parts; so, in this sense, there is a “universal car nature”
(Newton 1999). However, precise, correlated changes in these
parts can dramatically change the characteristics of a car.
Humans, like cars, are built from the same basic body plan.
They all have livers, lungs, kidneys, brains, arms, and legs.
And these structures are built from the same basic building
blocks, tissues, which are built of proteins, which are built of
amino acids, et cetera. However, small changes in the struc-
tures of these building blocks can lead to important and sci-
entifically meaningfuldifferences in function. For example, as
we noted in the “Introduction,”small changes in the tissue
distribution of the Inuit allow them to withstand the brutally
cold winters of the Arctic. It would literally be impossible to
answer fully the question of how the Inuit endure the Arctic or
how the Tibetans survive the plateaus without exploring these
differences—without, in other words, analyzing humans at a
The human brain is the same as the human body in this
regard and is not somehow immune tonatural selection. Or, as
Nicholas Wade (2014)succinctlynoted,“brain genes do not
lie in some special category exempt from natural selection.
They are as much under evolutionary pressure as any other
category of gene”(p. 106). It is almost certain that human
populations vary psychologically in interesting, important,
and scientifically meaningful ways because they were subject
to different selective regimes (Rushton 1985; Wade 2007). To
preview one example briefly, natural selection may have
slightly dialed up the general intelligence knob on
Ashkenazi Jews (i.e., an adjustment on an existing adapta-
tion), who score roughly 110 on standardized intelligence tests
(Cochran et al. 2006; Lynn 2011). Whether humans share a
universal psychological profile depends upon the question one
is trying to answer. If, for example, one wants to know how
humans learn to recognize siblings, the concept of a panhu-
man psychical nature is probably fruitful (Lieberman et al.
2007). If, however, one wants to know why the Ashkenazim
prosper in many societies, often despite virulent anti-
Semitism, then the concept of a universal psychical profile is
not only wrong, but it also positively prevents researchers
from accurately answering the question (because it leads to a
fruitless exploration for sociocultural causes which cannot be
the entire story).
Because the argument that human populations vary in
psychologically interesting ways is crucial for what fol-
lows, let us consider it more closely. We have noted that
evolution can work quite rapidly. Lizards placed on dif-
ferent islands, for example, can develop slightly different
responses to potential predators in only 30 or so genera-
tions (roughly 600 years for humans). We have also noted
that human populations have occupied different ecological
and climatic niches for many thousands of years. Last, we
have noted that human populations differ from each other
in many biologically interesting ways. If these three
points are correct—and almost nobody would dispute
them, then a nearly inescapable conclusion follows: hu-
man minds also vary among populations in interesting and
meaningful ways. Why? Because cognitive and affective
proclivities are every bit as crucial as anatomical and
physiological structures and processes for adaptively
responding to the world (including to other people). The
invention of agriculture and the rise of early civilizations,
for example, created selective regimes that shaped
existing cognitive traits, possibly including self-control
and general intelligence (Frost 2010;Frostand
An agricultural lifestyle might favor planning for the fu-
ture and inhibiting impulses more than a hunter-gatherer
lifestyle (not killing a cow today so that one can get
cheese, yogurt, milk, and more meat tomorrow; Cochran
and Harpending 2009). Of course, this line of speculation
might be incorrect. It may turn out that agricultural soci-
eties do not reward self-control in this way. But the hy-
pothesis is plausible, and the alternative hypothesis,
namely that agricultural and hunter-gatherer lifestyles cre-
ate quite similar selective regimes for cognitive and emo-
tional traits is less plausible.
Below, we forward a couple potential examples of biolog-
ically based human population differences in psychological
traits. As we warned before, these are not definitive examples.
They may turn out to be entirely sociocultural in origin.
However, it is plausible that they are at least partially geneti-
cally caused and, therefore, researchers should further explore
Self-construal Styles and Individualism/Collectivism
There are cultural/population differences in how people define
themselves and their relations with others, called self-
construal style (Markus and Kitayama 2010). For simplicity,
one can think of self-construal as a continuum, with indepen-
dent self-construal on one end and interdependent self-
Evolutionary Psychological Science (2017) 3:159–180 169
construal on the other. People who have an independent self-
construal tend to see themselves as autonomous, unique, and
separate from other individuals, whereas people who have an
interdependent self-construal style see themselves as inherent-
ly connected and enmeshed with others (Triandis 1995).
These self-construal styles are associated with different cul-
tures. Individualistic cultures are associated with independent
self-construal styles; collectivist cultures are associated with
interdependent self-construal styles.
Different regions and population groups tend to be
associated with different construal styles and cultures.
Northeast Asian cultures and peoples (China, South
Korea, Japan) tend to score high on collectivism and
interdependence, whereas Anglosphere cultures and peo-
ples (Australia, Canada, New Zealand, UK, USA) score
high on individualism (for some dissenting evidence and
discussion, however, see also Oyserman et al. 2002).
Many social scientists interpret the different construal
styles as entirely cultural in origin, and they interpret
the cultural differences as stemming from accidents of
history (i.e., Confucianism versus Enlightenment) or ge-
ography (Nisbett 2004;Triandis1993). In other words,
most researchers in the social sciences contend that dif-
ferences among human populations in construal styles
are entirely environmentally caused.
However, more recent research suggests that biologi-
cal differences among populations might contribute to
their different cultures and construal styles. For
example, Chiao and Blizinsky (2010) found a strong re-
lation between the prevalence of a serotonin transmitter
gene (SLC6A4) polymorphism and collectivism.
Specifically, they found that populations with more car-
riers of the short 5-HTTLPR polymorphism were more
collectivistic than populations with fewer carriers. The
short 5-HTTLPR polymorphism is associated with vari-
ous proclivities that, taken together, might be called
emotional sensitivity, including increased negative emo-
tion, harm avoidance, attentional biases to negative infor-
mation, sensitivity to cues of rejection, and augmented
risk for depression when exposed to environmental
stressors (Caspi et al. 2003; Chiao and Blizinsky 2010;
Karg et al. 2011; Way and Lieberman 2010;butsee,
Risch et al. 2009). Chiao and Blizinsky (2010)and
Way a n d L i e b erman (2010) argued that emotional sensi-
tivity might give rise to collectivistic cultures and inter-
dependent construal styles because collectivism creates
an emotional support system that buffers sensitive phe-
notypes from damaging emotional stress and loneliness.
Furthermore, emotional sensitivity and risk-aversion
might support collectivism because people with those
traits are less likely to challenge authority, assert creative
ideas, or demand independence from others. (Researchers
have found other polymorphisms that might explain
differences between Eastern and Western cultures, but
the 5-HTTLPR is a good example of this literature).
If the line of argumentation above is correct, cultural dif-
ferences between Northeast Asians and Western Europeans
are at least partially a result of biological differences. Of
course, this does not mean that culture is mechanistically de-
termined by biology, and neither does it mean that culture does
not influence cognition and behavior (Markus and Kitayama
2010). It simply means that some cultural differences among
human populations are caused by small biological/
psychological differences among those populations (Wade
2014). These cultural differences probably then reinforce the
small biological/psychological differences, creating larger dif-
ferences in cognitive processes (e.g., construal styles) and af-
fective propensities (see Fig. 1). Also, once a population cre-
ates a culture, that culture can become an evolutionary selec-
tive force (denoted by the dashed and bolded arrows flowing
in both directions), which augments population differences
(Richerson et al. 2010).
Ashkenazi Jewish Intelligence
Psychometricians have long documented differences among
populations on intelligence test scores (IQ) (Herrnstein and
Murray 1994;Jensen1998; Loehlin et al. 1975; Lynn 2015).
One of the most remarkable of these differences is that
Ashkenazi Jews (Jewish people from Northern and Eastern
Europe and their descendants) score roughly 7–15 points (al-
most a full standard deviation) higher than other Europeans
(Caucasians). In a review of Jewish intelligence and
achievement, Lynn (2011) put the average IQ of Ashkenazi
Jews at 110, which we will adopt for this article. Not only have
psychometricians noted high Jewish intelligence, but other
researchers have also recognized that Jewish people have ob-
tained exceptional socioeconomic status and achieved emi-
nence in many intellectual spheres, often despite facing cen-
turies of ubiquitous hostility and racism (Lynn 2011;Lynnand
Longley 2006; Murray 2003; Wade 2014). For just a few
examples, Jews are disproportionately represented among
chess grandmasters, Nobel Prize winners, Pulitzer Prize win-
ners, and Fields Medals winners (Lynn 2011). Most social
scientists have attempted to explain Jewish achievement using
exclusively sociocultural (e.g., an emphasis on intellectual
success and discipline) causal variables (Johnson 1988).
Although this genetic research is suggestive, caution is necessary given
recent evidence about the effects of single polymorphisms on complex quan-
titative traits. As Chabris et al. (2015) made clear when they introduced the
“fourth law of behavior genetics,”single alleles are likely to exert only minor
effects on complex polygenic traits. The reality of the small effect of single
alleles is reflected in the poor replication record of candidate gene studies, and
the tendency for false positives to emerge repeatedly in research testing the
effect of one gene on one behavior (Chabris et al. 2015). In thefuture, in might
prove more fruitful to examine the distributions and frequencies of numerous
trait relevant genes, not simply a handful of them.
170 Evolutionary Psychological Science (2017) 3:159–180
Recently, however, several researchers have argued that
Ashkenazi Jewish intelligence is not entirely socioculturally
caused, but rather is the result of unique selection pressures
faced by the ancestors of modern Ashkenazi Jews (Cochran
et al. 2006;Glad2011; Lynn and Kanazawa 2008).
Cochran et al. (2006), for example, contended that because
Ashkenazi Jewish people between 800 and 1700 were largely
endogamous and were forced into a few, cognitively challeng-
ing occupations (e.g., accounting, money lending, and man-
agement), there were strong selective pressures on Ashkenazi
Jewish intelligence. That is, because Ashkenazi Jews who
were highly intelligent flourished in their limited occupational
niche, they reproduced more prolifically than less intelligent
Ashkenazi Jews, which ultimately led to a population level
increase in intelligence. Lynn (2011) and Glad (2011)have
also forwarded evolutionary accounts of Ashkenazi Jewish
intelligence. Lynn’s discussion is probably the most ecumen-
ical, accepting multiple causal pathways to high Ashkenazi
intelligence, including eugenic practices, occupational niche
selection, and persistent persecution. Whatever the ultimate
causal story, the evidence does suggest that Ashkenazi intelli-
gence is at least partially genetically caused.
Intelligence is a highly heritable trait (a statistic that reflects
genetically underpinned trait variation, and which is not to be
confused with “inherited.”See Sesardic (2005) for more de-
tail). Most studies find that between 50 and 80% of within-
population differences in intelligence is caused by differences
in genes (Bouchard 2013; Jensen 1998; Plomin and Deary
2015). Although heritability measures cannot be uncritically
applied to group differences (Block 1995), the high heritabil-
ity of intelligence suggests that large group differences might
be at least partially genetically caused (Sesardic 2005). Lynn
(2011) notes that Ashkenazi Jewish intelligence scores are
relatively similar wherever they are measured. Furthermore,
Ashkenazi Jewish people tend to have high levels of achieve-
ment in every country they inhabit, often despite facing fierce
anti-Semitism. Cochran et al. (2006) also noted that
Ashkenazi Jewish people are vulnerable to a number of dis-
eases and genetic disorders that are related to the growth of
axons and dendrites and potentially to higher intelligence
(Charrow 2004;Hartgeetal.1999). Many of these diseases
are deleterious, so there seems to be a tradeoff between the
potential for high intelligence and the risk of debilitating ill-
ness or even pre-reproductive mortality.
Of course, this evidence is not dispositive. But it is strongly
suggestive. And if true, it means that at least part of the IQ gap
between Ashkenazi Jews and other populations is genetic in
origin. It is important to note that this does not mean that all of
the gap can be explained by genetics. Nor does it mean that
there are not sociocultural causes of Jewish intelligence and
achievement (e.g., motivation for achievement; see Lynn
2011). It simply means that some of the intelligence differ-
ences among Ashkenazi Jews and other human populations
are genetically caused as a result of natural and sexual
These two examples suggest that culture is, to some degree,
an extension of the human phenotypes that comprise it
(Laland 2004). Small differences in biological predispositions
may lead to cultural differences among human populations. Of
course, this does not mean that all cultural differences are
caused by subtle genetic differences. But some might be (for
additionalinsight regarding a connected research question, see
also Evans et al. 2005,aswellasMekel-Bobrovetal.2005).
A full integration of human biological diversity into the evolu-
tionary social sciences will give rise to a reimagined Darwinian
paradigm of research (Winegard and Winegard 2014). This cer-
tainly does not mean that the standard evolutionary psycholog-
ical paradigm is otiose or needs to be completely overturned. It
is not and does not. But some of its basic assumptions will have
to be revised. Here, we will lay out six basic principles of this
new Darwinian paradigm (see also, Boyd and Richerson 1985;
Cochran and Harpending 2009; Laland et al. 2010; Lynn 2006;
1. Variation is the grist for the mill of natural selection and is
ubiquitous within and among human populations.
Fig. 1 Diagram of how human populations can diverge in evolutionary
history. A human population first splits into two groups in different
environments with different ecological and climatological forces. This
creates different selective pressures on the populations (which can
eventually shape their genomes, altering allele frequencies across
groups). The different environments can also lead to different cultural
systems, which also create different selective pressures
Evolutionary Psychological Science (2017) 3:159–180 171
2. Evolution by natural selection has not stopped acting on
human traits and has significantly shaped at least some
human traits in the past 50,000 years.
3. Current hunter-gatherer groups might be slightly different
from other modern human populations because of culture
and evolution by natural selection acting to influence the
relative presence, or absence, of trait-relevant alleles in
those groups. Therefore, using extant hunter-gatherers as
a template for a panhuman nature is problematic.
4. It is probably more accurate to say that, while much of human
nature is universal, there may have been selective tuning on
various aspects of human nature as our species left Africa and
settled various regions of the planet (Frost 2011).
5. The human brain is subject to selective forces in the same
way that other organ systems are. Natural selection does
not discriminate between genes for the body and genes for
the brain (Wade 2014).
6. The concept of a Pleistocene-based environment of evo-
lutionary adaptedness (EEA) is likely unhelpful (Zuk
2013). Individual traits should be explored phylogeneti-
cally and historically. Some human traits were sculpted in
the Pleistocene (or before) and have remained substantial-
ly unaltered; some, however, have been further shaped in
the past 10,000 years, and some probably quite recently
(Clark 2007). It remains imperative to describe what se-
lection pressures might havebeen actively shaping human
nature moving forward from the Pleistocene epoch, and
how those ecological pressures might have differed for
different human populations.
These principles lead to a number of consequences, some of
which are obvious, and some of which are subtler, that are
relevant to many disciplines including anthropology, criminolo-
gy, economics, history, psychology, and sociology. Below, we
consider a few of the most important consequences and describe
what this Darwinian research program might look like.
Hunter-Gatherers and Human Nature
Although most researchers warn that hunter-gatherer peoples
should not be treated as preserved relics of a human nature
unsullied by the influences of civilization, in practice, some
prior scholarship treats them exactly that way (Geher 2013;
Zuk 2013). And it is very seductive to think of hunter-
gatherers as more representative of human nature than people
living in industrialized societies as is illustrated by the remark-
able number of popular articles and books that use hunter-
gatherer behavior as a guide to the essence of human nature
(see, e.g., Connor 2013;DeVany2010; Diamond 2013).
From the perspective of a Darwinian paradigm based on the
principles listed above, this is misguided because humans who
evolved in civilizations may be slightly different, psychological-
ly, from humans who did not (Cochran and Harpending 2009).
Equally unnecessary is the promotion of the concept of a
mismatch between modern societies and “stone age”brains
(Diamond 2013; Tooby and Cosmides 2005;Zuk2013). The
idea is that human brains evolved many, many thousands of
years ago, but that human civilization is only roughly 4000 years
old; therefore, human brains are not “designed”to deal with
many of the challenges of modern civilization. Of course, the
concept of mismatch is not entirely wrong. It does take time for
the brain to evolve, even if the time is shorter than many re-
searchers have presumed. So, modern food systems (fast food,
processed food, readily available food) probably present unique
challenges to humans who spent most of their evolutionary
history in environments where calorie-rich food was reasonably
difficult to obtain (Birch 1999). However, research has argued
that some human populations were significantly shaped by civ-
ilization (which is most certainly true to some extent), becoming
more peaceful and perhaps even more “capitalistic”during the
process (Clark 2007; Frost and Harpending 2015;Wade2014).
In other words, some traits in some human populations are
reasonably well attuned to many of the features of market-
Consequences of Ignoring Population Differences
Most social scientists steadfastly ignore human biological di-
versity (Boutwell et al. 2015), but if the six principles we listed
are correct, this is a mistake that might impair the ability of
social scientists to promote productive research programs.
Consider a couple of examples.
In a meta-analysis of racial and ethnic differences in self-
esteem, Twenge and Crocker (2002) found a pattern of self-
esteem differences (Blacks scored higher than Whites after the
1980s and Asians scored lower than both), but ruled out, a
priori, the possibility that such differences were related to
biology because, according to them, “racial and ethnic cate-
gorizations are socially constructed”and are not based on
“shared biological characteristics”(p. 371). This means that
an entirely legitimate and plausible hypothesis about the eti-
ology of self-esteem differences was ignored, leaving only
social or cultural hypotheses. It is, of course, possible that
the differences are entirely environmental in origin, but it is
not certain, and ruling legitimate hypotheses out a priori on
flimsy arguments (see “Race and Human Populations”sec-
tion) about the nonreality of human biological diversity po-
tentially prevents researchers from fully understanding the
causes of differences in self-esteem.
In a paper on racial and ethnic differences in violent crime
rates, Sampson et al. (2005) asserted that biological differ-
ences among human populations do not hold “distinct scien-
tific credibility as causes of violence,”and proceeded to adju-
dicate between three environment-only hypotheses about the
causes of disparities in violence (p. 224). So, again, these
researchers ruled out a priori a perfectly legitimate and
172 Evolutionary Psychological Science (2017) 3:159–180
plausible hypothesis and proceeded to approach the data with
a self-imposed theoretical limitation. Of course, it could turn
out that the etiology of the disparities in crime rates is entirely
environmental. But it is not really scientific to address the
problem without carefully considering all potential causes
How the Research Program Would Work
A paradigm that accepted the reality of human biological di-
versity would not a priori dismiss hypotheses about biological
causes for population differences; however, it would also not
assume that all population differences are biologically caused.
Population differences are, of course, caused by myriad vari-
ables and many population differences are the result of an
interaction of biological, environmental, and cultural factors.
Some differences, however, might be entirely cultural in ori-
gin (differences in the side of the road people drive on, or in
food utensils, probably fall in this category); other differences
might be almost entirely biological in origin (differences in
hair texture, skin color, lactose tolerance, probably fall in this
category). Because the variables that cause human population
differences are often tightly intertwined and almost impossible
to extricate from each other, research on the causes of group
differences will be arduous, tentative, and slow. A careful
description of the methodological principles of this kind of a
Darwinian research program would require the length of a
book, but we can highlight several of the most important.
1. The first way to approach biological variation is to look
for differences among human populations. Many re-
searchers already do this, but they almost invariably ig-
nore the possibility that such differences are at least par-
tially biological in origin (see Sampson et al. 2005;
Twenge and Crocker 2002 for two prominent examples).
To assess better human population variation, it is neces-
sary that social scientists broaden their samples to include
individuals from many societies and cultures and continue
the practice of collecting data on race and ethnicity (Chiao
et al. 2013; Henrich et al. 2010;Jensen2012).
2. After researchers find examples of population differences,
they should approach causal analyses neutrally. That is,
researchers should not assume that population differences
are sociocultural in origin; they should, instead, adopt a
Bayesian approach, assuming, at a minimum equal prior
probabilities for biological and sociocultural causal vari-
ables (Rowe and Rodgers 2005) and updating their beliefs
on the basis of theoretical and empirical evidence. As we
noted above, Twenge and Crocker (2002) should not have
assumed that only sociocultural explanations of self-
esteem differences are possible. Biological causes are pos-
sible as well, and there is no a priori reason to favor either
set of explanatory variables.
3. To continue the exploration of population differences, re-
searchers should consider a broad range of data and theory
to estimate the plausibility of biological causal variables.
Are there other biological differences among the popula-
tions in question? Is the trait highly heritable? Does it
cohere with a pattern of differences among the groups?
Consider the self-esteem example again. First, there are
many biological differences among Blacks, Whites, and
Asians (Molnar 2006;Rushton1995; Sarich and Miele
2005). Second, self-esteem is at least moderately heritable
(Jonassaint 2010; Neiss et al. 2006). And third, the differ-
ences in self-esteem, Blacks highest, Asians lowest, and
Whites in the middle, do appear to cohere with a suite of
hypothesized and known differences among the groups
(Rushton 1995; Meisenberg and Woodley 2013;Minkov
and Bond 2015; Templer 2008). Therefore, it may be
reasonable to hypothesize that at least some of the differ-
ences in self-esteem among Blacks, Whites, and Asians
are biologically caused (see also Boutwell et al. 2015 for
an example related to antisocial behavior). Of course, this
hypothesis might be disconfirmed by later exploration
and analysis, but it is plausible and productive.
4. Researchers should test the posited biological cause in
more depth. One should not assume, as we mentioned
earlier, that differences emerging between human groups
are necessarily sculpted by natural selection. Indeed, it
will be difficult in many cases to confidently assert that
differences are the product of directional selection and not
some alternative force (e.g., genetic drift, developmental
plasticity, etc.). It may also be reasonable to assume that a
guiding “null hypothesis”in the absence of strong evi-
dence (gathered from research techniques) should be that
something other than natural selection—culture, develop-
mental plasticity, etc.—is the ultimate cause of group
Experiments on biological differences are difficult to
conduct and are not often feasible. Yet, it is often possible
to examine relevant adoption studies, cross-cultural stud-
ies, and possibly even genetic (i.e., identification of al-
leles or haplotypes) studies (genome-wide data becomes
increasingly available for various population groups). The
first two forms of studies might indicate that the putative
biological variable is actually sociocultural, thus provid-
ing reasonably stringent tests of the biological hypothesis.
For example, if Asians raised in homes with White par-
ents displayed self-esteem levels equal to the White pop-
ulation mean, then the biological hypothesis, though not
completely falsified, would lose plausibility. Or, if Asians
who grew up in the USA had self-esteem levels similar to
the White mean, the biological hypothesis would again
lose plausibility. Genetic studies are sparse because it is
difficult to isolate alleles that are correlated with
Evolutionary Psychological Science (2017) 3:159–180 173
psychological traits and many such studies fail to replicate
(Bosker et al. 2011; Chanock et al. 2007; Duncan and
Keller 2011). But, as genetics research matures, it will
provide valuable evidence for (or against) biological
For now, the most likely scenario is one in which the priors
about causal variables gradually shift as evidence is examined
and collected, but a great deal of uncertainty will remain be-
cause the evidence is not as strong as researchers would like
(see Fig. 2).
One might wonder why researchers should embrace such a
Darwinian paradigm given that it is unlikely to recompense
them with certain knowledge about the etiology of various
population differences. The answer is simple: because it will
provide a fruitful research program that will shape future re-
search and theorizing in productive ways. So, although the
causal variables responsible for specific population differ-
ences may remain unknown for the foreseeable future, an
honest examination of potential biological causes will spur
new research and new theorizing that will produce new data.
Of course, many traits are relatively the same across human
populations and many of the cognitive and emotional systems
researchers care about can be approached from the universalist
perspective of the SEPP. Our argument is not that the SEPP is
entirely wrongheaded, but just that it is unfruitful when ap-
plied to certain questions and should, therefore, be revised.
Before concluding, we want to address the ethical concerns
that have been raised about candidly studying and discussing
human biological diversity. Probably, no other area of research
in the social sciences has caused more fractiousness than the
study of human population differences, especially the study of
differences in intelligence (Hunt and Carlson 2007). Some
researchers have even contended that the study of population
differences is so divisive and so dangerous that scientists of
good conscience should avoid it altogether (Hunt 1998;Rose
2009). Although we disagree with this advice, which we think
betrays the spirit of free scientific inquiry, we do understand
the concerns that arise when scientists study and candidly
discuss human population differences (Ceci and Williams
2009;Gottfredson2007). Those concerns can be addressed
without stifling scientific progress or slandering researchers
who decide that the study of human biological diversity is
inherently interesting and worth pursuing.
Contrary to the bold claims of some scientific absolutists
(see, e.g., Gottfredson 2007;Kanazawa2008), science is not
an autonomous domain of intellectual activity (Connor 2005;
Lewontin 1991). Science is a human social practice and is part
of a larger social system. Scientific theories and knowledge
have social consequences. Knowledge of the nature of sub-
atomic particles, for example, released the devastating energy
of the atomic nucleus and allowed the invention of nuclear
weapons, which have threatened planetary destruction for
more than 50 years. Clearly, this knowledge had dramatic
ramifications and the researchers who were involved in the
development of nuclear weapons carefully and cautiously
reflected upon its potential consequences (Rhodes 2012).
Similar concerns may apply to the study of population differ-
ences. If, for example, the dissemination of information about
population differences would increase the chances of the en-
actment of intolerant social policies, researchers should be
cautious about studying those differences and promulgating
the results to the public.
There are, indeed, some potentially negative consequences
of promulgating information about human population differ-
ences. However, these risks are outweighed by the potential
costs of not studying and speaking responsibly about popula-
tion differences. Some population differences are relatively
conspicuous (skin color) and some are easily deducible (dif-
ferences in intelligence, whatever the cause), which can lead
to uninformed and often hateful theories as well as irrespon-
sible and insensitive writings (see, e.g., Kersey 2012; Taylor
2011). If researchers do not responsibly study and discuss
population differences, then they leave an abyss that is likely
to be filled by the most extreme and hateful writings on pop-
ulation differences. So, although it is understandable to have
concerns about the dangers of speaking and writing frankly
about potential population differences, it is also important to
understandthe likely dangers of not doing so. It is not possible
to hide the reality of human variation from the world, not
possible to propagate a noble lie about human equality, and
the attempt to do so leaves a vacancy for extremists to fill.
Furthermore, studying and discussing human population
variation can be beneficial because it increases our knowledge
about the human species, about the causes of social outcomes,
Fig. 2 Steps for studying human biological diversity. See text for more
details about each step
174 Evolutionary Psychological Science (2017) 3:159–180
Tishkoff and Kidd 2004). It may be unpleasant to our moral
sensibilities to discover that some human population groups
have higher susceptibilities to certain diseases or to social
problems in modern societies, but we cannot correct these
and other problems if we do not know their etiologies.
Suppose, for example, that Blacks in the USA and the UK
are more likely to suffer from hypertension than Whites
(Carson et al. 2011; Lane and Lip 2001). The only way we
can address that problem is by sedulously studying the causes
of the differences in hypertension. It might turn out that the
causes are entirely environmental. But it might also turn out
that Blacks have genetic profiles that make them more suscep-
tible to hypertension than Whites. Denying the reality of this
biological difference would then be positively pernicious,
delaying important interventions that could ameliorate the
problem. The same holds for population disparities in crime
rates (Beaver et al. 2013; Jones-Webb and Wall 2008;Rushton
and Templer 2009). If researchers do not carefully study the
etiology of these population disparities, then they cannot fully
address or propose solutions to the problem. It may be
comforting to ignore such issues, but it is not beneficial to
the populations involved.
If researchers responsibly educate the public about hu-
man population variation and philosophers and ethicists
and politicians discuss it within a broader narrative of
tolerance, the study of human population differences
can not only be fruitful but also uplifting (Crow 2002).
Variation is the rule in nature. No two leaves are the
same. No two humans are the same. And no two human
populations are the same. Instead of lamenting this, we
should celebrate it just as we celebrate the rest of the
vast and diverse biological world. Humans are not an
exception to, but a part of, that almost endlessly varie-
gated tapestry (Wilson 2010).
To conclude, we believe that:
1. It does not promote the interests of society or of science to
deny that human populations vary in biologically mean-
ingful ways simply because it makes some people uncom-
fortable or anxious.
2. If some scholars deny the reality of human population
variation and slander those who wish to study and discuss
it openly, then extremists are likely to monopolize the
3. There is no reason why those who promote cultural diver-
sity and tolerance cannot simultaneously embrace the re-
ality of biological diversity.
4. Both culture-only hypotheses and genetic-based hypothe-
ses can be dangerous when misappropriated by politi-
cians and social theorists (Pinker 2003).Researchers
should be cautious about forwarding any hypotheses that
have potential social ramifications and should be temper-
ate in rhetoric and humble in practice.
In this article, we have argued that social scientists should
integrate human biological diversity into their research pro-
grams. Specifically, we focused on the SEPP because it is
probably the most successful social science paradigm to date.
We contended that the SEPP is flawed because it has not fully
assimilated the reality of biological diversity into its general
framework (Cochran and Harpending 2009;Zuk2013). It is
important to note that some prominent researchers have
attempted to do just this (e.g., Gottfredson 2002;Hart2007;
Herrnstein and Murray 1994; Lynn 2015;Meisenberg2012).
Rushton (1995), for example, forwarded an expansive account
of population differences based on life-history theory.
However, he was viciously attacked by many scholars (e.g.,
Barash 1995), and his work was quickly marginalized.
Comparable fates befell other researchers who made similar
suggestions. Some of these researchers, including Rushton,
were probably less conciliatory than they could have been,
but they nevertheless deserve recognition for important con-
tributions to the endeavor to understand humans, and they
certainly did not deserve the obloquy they received
We are not naive about the obstacles a Darwinian approach
to human biological diversity faces. We hope only to start a
candid discussion and to forward some suggestions about how
to proceed with this paradigm. Doubtless, some will continue
to resist the notion that human populations differ in biologi-
cally meaningful ways. But it seems clear to us that biological
diversity is the rule across the vast tapestry of life. It is true
among plants, among animals, among humans, and among
human populations. Instead of nervously ignoring it, we
should actively celebrate it.
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