Evolved Brains in Evolved Bodies
Human populations differ in psychological as well as physical traits.
In his Pulitzer Prize-winning book Guns, Germs, and Steel, Jared Diamond seeks to explain the ultimate causes of modern societies’ clear disparities in wealth and power. “It is perfectly obvious to everyone,” Diamond points out, “that different peoples have fared differently in history.” But why? One popular explanation for “all those glaring, persistent differences in peoples’ status,” he suggests, “involves implicitly or explicitly assuming biological differences among peoples.” Yet such assumptions, he argues, are not merely wrong but racist.
Diamond accepts that for many people it could still “seem logical to suppose that history’s pattern reflects innate differences among the people themselves”:
We’re told that [inter-group inequality] is to be attributed not to any biological shortcomings but to social disadvantages and limited opportunities. Nevertheless, we have to wonder. … We’re assured that the seemingly transparent biological explanation for the world’s inequalities … is wrong, but we’re not told what the correct explanation is.
Unless there is “some convincing, detailed, agreed-upon explanation for the broad pattern of history,” Diamond suggests, “most people will continue to suspect the racist biological explanation is correct after all.” His guns, germs, and steel thesis is an attempt to provide just such a detailed and convincing counterargument to these widespread yet supposedly racist beliefs about the causes of present-day global disparities.
In the quarter century since Guns, Germs and Steel was published, Diamond’s deservedly lauded “science of human history” theories have become increasingly influential, inspiring anthropologist Joseph Henrich, author of The WEIRDest People in the World and public intellectual Yuval Noah Harari, among others. And while Diamond’s thesis has also received its share of criticism, one central tenet of the book—the dismissal of biological explanations of social inequalities as racist—has become more entrenched than ever.
Yet the past 25 years have also witnessed an explosion in our understanding of human genetics and genomics. Recent insights into our own species’ evolved biology fatally undermine this key aspect of Diamond’s argument: his rejection of the possibility of meaningful “biological differences among peoples.” Despite growing genetic evidence, however, the very idea of significant genetic variation between human populations is still routinely rejected. This attitude is, however, only likely to perpetuate the “glaring, persistent differences” that concerned Diamond and trouble so many other well-meaning egalitarians.
To grasp why, we can start by examining an unintended inconsistency in Diamond’s own reasoning.
“Why did wealth and power become distributed as they are now, rather than some other way?” Diamond asks in the introduction to Guns, Germs and Steel. “For instance, why weren’t Native Americans, Africans, and Aboriginal Australians the ones who decimated, subjugated, or exterminated Europeans and Asians?”
Diamond’s answer is that geographical and environmental factors—in particular, the global distribution of domesticable plant and animal species—played a pivotal role in shaping the development of human societies. These factors provided Eurasian populations with crucial advantages, enabling them to pioneer agriculture, support larger populations, develop immunity to diseases, and exchange ideas and innovations over vast geographical areas. One of Diamond’s key claims here is that technologies and knowledge—as well as diseases and resultant immunities—spread more easily across Eurasia’s climatically and environmentally similar east–west axes, whereas such diffusion was nearly impossible along the north–south axes of Africa and the Americas.
According to Diamond, these accidents of history and biogeography gave Eurasians—particularly Europeans—an overwhelming advantage in technology (“guns and steel”) and disease resistance (“germs”) over indigenous populations during the period of European global expansion from the late 15th century onwards. For instance, Diamond suggests that newly introduced Eurasian diseases such as smallpox wiped out over 90 percent of the indigenous populations of the Americas before European settlement proper had even begun, making later colonisation and conquest relatively easy.
Although there is an obvious biological aspect to Diamond’s argument—that Europeans’ immunity to the diseases that later devastated indigenous peoples evolved through natural selection—Diamond nevertheless insists that other aspects of human biology, and in particular the possibility of evolved psychological differences between racial groups, played no part in creating the obvious divide between the modern world’s haves and have nots.
Yet here Diamond’s argument becomes inconsistent. While on the one hand denying evolved population divergence in cognitive characteristics, on the other he argues that indigenous peoples—such as native New Guineans—might actually be more intelligent than modern Europeans. In Eurasia, he suggests, the primary selection pressure since the advent of agriculture has been disease resistance in ever-denser populations. The more sedentary lifestyles and greater political centralisation of Eurasian societies, by mitigating natural environmental hazards, would also have reduced selection for intelligence. By contrast, over the same time period in smaller traditional societies like those of Papua New Guinea, selective pressure on intelligence would have remained constant in the face of persistent environmental challenges, such as chronic tribal warfare, resource procurement problems, natural disasters, and the like. The likely result? Dumber, more docile Europeans and smarter Indigenes. Regardless of the validity of these conclusions, Diamond unintentionally demonstrates that natural selection for intelligence between racial groups is plausible.
Diamond’s inconsistency here reflects a broader internal contradiction in the thought of many liberals and progressives: that while natural selection may have shaped human biology and psychology over the long stretch of evolutionary time, it hasn’t much affected our psychological traits—at least not since our species began expanding out of Africa around 50,000 years ago. Thus while left-leaning thinkers would perhaps accept that superficial physical differences between racial groups emerged as a result of humanity’s global dispersal, they often argue that our psychology has nonetheless remained largely unchanged. Palaeontologist Stephen Jay Gould epitomises this belief: “There’s been no biological change in humans in 40,000 or 50,000 years. Everything we call culture and civilisation we’ve built with the same body and brain.” Even many evolutionary psychologists support this idea of what Gould calls the “psychic unity of humanity.” While environmental challenges may have varied widely between dispersed human groups, they suggest, the social and cognitive challenges that individual humans faced—such as mate selection, alliance formation, and child-rearing—stayed much the same, making significant cognitive and psychological divergence between populations unlikely.
Such beliefs about the cognitive similarity of all human groups are understandable given the long and troubling history of racist claims about the intellectual superiority of some races over others. Moreover, referencing human biology in discussions of inter-group inequality seems to blame the victims of both past conquest and colonisation and of present-day prejudice and marginalisation. Again, this attitude is fully understandable. Ill-considered theorising about evolved cognitive differences between racial populations could cause real social harm, especially if it leads people to conclude that nothing can be done to address the “glaring and persistent” status inequalities between different groups. In the minds of many “left-leaning social scientists,” therefore, as Kathryn Paige Harden has noted, “behavior-genetics research, no matter how well intentioned, [is] likely to lead us down the garden path to eugenics.”
Yet some divergent evolution of both body and brain between long-separated human populations seems to follow directly from Darwin’s concept of “descent with modification.” Indeed, for sociobiologist E.O. Wilson, this is an inevitability: “Given that humankind is a biological species, it should come as no shock to find that populations are to some extent genetically diverse in the physical and mental properties underlying social behavior.” Today’s genetic and genomic advances have confirmed the accuracy of Wilson’s statement. Our growing understanding of human evolution indicates that the progressive position on psychological equivalence is becoming increasingly untenable. It is time to accept that differences in psychological traits probably exist between both individual humans and between human populations. Recognising this could enable us to do more good for marginalised people and populations than censure and denial have achieved. By embracing genetic insights we could also better address the inequalities that Diamond describes but does not fully explain.
Jerry Barnett
Before explaining why, let’s begin with some of the recent evidence that our minds, as well as our bodies, have changed since humans began to disperse across the planet.
Evidence of divergent physical and cognitive evolution across human populations continues to grow. The following studies provide just a few examples of the evidence of this.
Earlier this year, research revealed that genes inherited from Denisovans—an extinct sister species to Neanderthals, inhabiting eastern Eurasia—have been crucial for the later adaptation and survival of two distinct human populations in Papua New Guinea. According to the study, lowland New Guineans’ Denisovan genes enhance their immunity to infections, while highlanders benefit from different Denisovan genes that help them cope with altitude in the mountainous interior of the island. These findings build upon earlier groundbreaking research that first linked Denisovan genes to the ability of modern populations living on the Tibetan plateau to thrive at extreme altitudes. As the BBC reported at the time, this was “clear and direct” evidence of humans “adapting to new environments through genes acquired via interbreeding with other human species.” The relevant point here, however, is that this is also clear and direct evidence of divergent evolution in distinct human populations.
The BBC report on the original Denisovan research also suggested that interbreeding with other ancient humans—such as with the Denisovans’ sister species in western Eurasia, the Neanderthals—may have “introduced genes that may help [modern humans] cope with viruses outside Africa.” This has been further supported by more recent findings linking certain Neanderthal genes to increased severity of COVID-19. Importantly, these inherited genetic differences vary between populations. Modern South Asians, especially Bangladeshis, are more likely to carry the specific Neanderthal genes linked to COVID-19 than other groups. These genes may have offered immunity benefits in the past but now exacerbate the effects of COVID-19. Similarly, the apparently higher susceptibility to HIV/AIDS among African populations may result from genes that once provided resistance to historical diseases. Once again, this supports the reality of divergent evolution among human populations.
Of course, these examples of population differences in disease resistance align with Jared Diamond’s Guns, Germs, and Steel thesis—that evolved disease resistance shaped the fortunes of different peoples—and do not necessarily imply behavioural or cognitive differences. However, other emerging genetic evidence suggests that such cognitive divergence may also have occurred.
One recent study concludes that behavioural differences in people’s body clocks may originate in Neanderthal genes. According to the research, some modern human populations may have inherited these psychological dispositions, in part, from Neanderthals who, unlike early Homo sapiens, evolved at higher latitudes with more seasonal daylight change: “And that genetic legacy may still influence variation in the human body clock and chronotype—whether you’re a night owl or a morning lark—today.” Other recent research indicates “that specific Neanderthal genetic variants can influence autism susceptibility, suggesting a link between our ancient relatives and modern neurodevelopmental conditions.”
But it’s not just interbreeding with other closely related species that provides evidence of divergent cognitive and behavioural evolution. Tracing the genetic history of diseases in the more recent past has long been important for understanding and mitigating modern ailments. This established line of inquiry is now also shedding light on the origin of cognitive disorders. For example, recent studies exploring how “historical migration [is] linked genetically to predisposition to various contemporary illnesses” highlight the possible causes of psychological differences between separate European populations: “neolithic farmer lineage, more prominent in southern Europe” may be connected “to a greater disposition to anxiety, guilty feelings and irritability.” Related research reaches similar conclusions about the origins of certain cognitive traits, including mood disorders, in specific populations. Some geneticists are hoping to extend these lines of inquiry in future “to reveal more about the genetic markers of autism, ADHD, schizophrenia, bipolar disorder, and depression.”
The accumulating evidence of evolved differences in cognitive and behavioural traits should not come as a shock. Nor need it be as politically fraught as many progressives believe. Elsewhere, in a Quillette article co-authored with Jon Entine, I argue that reluctance to accept racial differences in susceptibility to disease is inflicting harm on marginalised communities. Much the same can be said of resistance to the idea of psychological and cognitive differences. As Marie Curie put it: “Nothing in life is to be feared, it is only to be understood. Now is the time to understand more, so that we may fear less.” If we are serious about addressing inequalities, we first need to understand their causes: historical, social, cultural, and genetic.
Jon Entine
This diversity is, of course, also seen between individuals. As social and environmental conditions become more equal, the differences in outcomes that are due to individual genetic differences will increase. Take schooling as an example. In socially unequal societies, where fewer people have the opportunity to go to school, genetic differences don’t explain much about differences in people’s educational attainment. Yet in more equal societies, such as those of the liberal West, where education is compulsory and the school environment is more similar for everyone, genetic differences can explain more about why attainment varies between individual students. As Kirsty Wilding, Megan Wright, and Sophie von Stumm argue in this meta-analysis of genetics and education: “The realization that eradicating environmental inequality will produce greater genetic inequality reads somewhat uncomfortable, yet it is true.” In other words, if we fail to take genetic propensities into account while striving to achieve equality of opportunity then we may merely exacerbate inequalities of outcome. Wilding et al conclude “that up to 25% of differences in school grades between individuals can be attributed to genetic differences.”
What, then, should or can be done to compensate for genetic disadvantage? When it comes to education, one obvious option is to change the “one size fits all” approach and instead tailor schooling to individuals’ cognitive abilities. At present, our mass education system primarily rewards those who can cope with its constraints, not just because they possess “smarts,” but because they are able to sit still and diligently jump through the hoops of homework, tests, and exams. In effect, the current Western education system favours those with the genetic propensity to succeed in that system and fails those who don’t.
Educational attainment—diplomas and certificates—correlates with later “real-life success,” including greater employment prospects, higher income, better health, and even happiness. From a conservative perspective, the current education system works: by allowing equality of opportunity, it winnows out those best suited for success in modern technological societies. However, by dismissing biological and genetic factors entirely, we risk missing important insights that could help address and mitigate social disparities.
