David Reich Nature Study Shows Recent Human Evolution

Human evolution, particularly of the brain, ended a long time ago—at least that is what many educated people, wary of claims about biological differences between human groups, prefer to believe. For much of the postwar era, it was widely assumed that natural selection had largely ceased to shape human populations and that any evolution during the past ten millennia was too slow or too slight to detect. That view was partly shaped by evidence and partly shaped by history. After World War II, the horrors of Nazi racial science made claims about human biological variation radioactive, and for good reason. But a justified rejection of racial typologies often hardened into a broader assumption: that natural selection had lost its grip on humans, and that differences between populations were mostly superficial.

A landmark study published in Nature in April has complicated that narrative. Drawing on ancient DNA from nearly 16,000 West Eurasians spanning 10,000 years, Harvard geneticist David Reich and colleagues found evidence that directional genetic selection is not only widespread but accelerating. Rather than stasis, evolution has continued to act on hundreds of genetic variants associated with traits ranging from disease risk and body composition to complex behavioural measures, including intelligence.

While the paper itself is technical and cautious, its implications are explosive. Importantly, the selection identified in the study occurred within populations inhabiting distinct ecological and cultural environments, suggesting that recent human evolution has been shaped by local selective pressures rather than a uniform global process. That, in turn, raises the possibility of ongoing regional divergence between different human groups. This has already dragged an older, more troubling word back into the discussion—“race”. This is not the sloppy popular notion based on skin colour or a rigid biological essence. Human genetics substantially overlaps among groups, rendering classical racial categories obsolete. But this provocative research does underscore that many human differences may not be simply skin deep.

For decades, the prevailing view held that while societies have transformed, the evolved architecture of our species has remained fixed since long before the first cities were built. The late palaeontologist Stephen Jay Gould put it like this in 2000: “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.” In this framework, any observed differences in group outcomes were presumed to be overwhelmingly environmental or sociological.

However, the Reich study suggests that the Holocene—our current geological epoch, which began approximately 11,700 years ago at the end of the last Ice Age—has not been a period of stasis at all. It has been a furnace of differentiation. Natural selection has been more pervasive, and more recent, than the Gouldian consensus allows. Psychological and cognitive traits long assumed to be universal can no longer, it seems, be cordoned off from the evolutionary processes that shaped skin colour, disease resistance, or lactose tolerance. These traits vary by population history. And while folk categories of race remain crude and biologically imprecise, the broader claim—that evolution somehow stopped at the neck—is becoming increasingly untenable.

Determining the strength of the evidence for recent selection on cognitive traits is ultimately a task for scientific inquiry. The more immediate issue is societal. Even raising the possibility of evolved cognitive differences provokes extraordinary resistance—and even outright moral panic—in ways unmatched in almost any other area of science. The notion that humans may vary biologically is so socially taboo that it can be difficult to even consider and examine the evidence. Researchers often operate under ideological and institutional constraints that extend well beyond purely empirical considerations. The result is a climate that narrows the boundaries of legitimate discussion, undermines trust in scientific institutions, and makes honest debate about human difference all but impossible.