Agency and Adaptation

In the history of the sciences, in history tout court, few books have dropped with greater thunder or left a greater wake than Charles Darwin’s On the Origin of Species. Although that famous book did not pluck the notion of evolutionary change ex nihilo, nor was  Darwin’s contribution as singular as streamlined narratives tend to present it, its publication was, nevertheless, a watershed moment. The pages of Origin helped to fuel a cultural and intellectual firestorm, one which has been burning ever since. Nor are the latter-day blazes of controversy restricted only to the dim quarters of American creationism or other social and intellectual fringes.

From fierce debates about the heritability and variability of human intelligence and questions about the ethical meaning of conditions such as Down syndrome to our present-day squabbles over the relationship between personal identity and physiological reality, the central issue remains what it ever was: the question of our existence as fundamentally embodied, biological creatures. Though Darwin wrote of The Descent of Man, we are by now perhaps more inclined to think of his Ascent. The conceit, unspoken but implicit, is that the evolutionary process is one from which we have now emerged. It may have produced our ancestors, but upon having produced them, it let go, leaving them to chart their futures entirely through cultural development and human innovation—processes of the mind, not the brute body. It is a flattering fable, but a fable all the same.

That we humans should be adept at modifying our environment is neither a new nor controversial notion, even if the full scope of our impact reaching back into far antiquity was not always truly grasped. The converse notion, however—that our environments should have modified, should continue to modify, us—is far less often discussed. To study selection, adaptation, and evolutionary change in other species is one thing; observing it in our own is rather different. It makes the gap between man and beast feel troublingly slight; it is a reminder that, for all that our minds may apprehend the deeper recesses of the cosmos, our bodies are very much animal. 

Genomic research into the basic biological nature of humans has been ongoing for some decades. The greatest milestone to date—one of the greatest in all the sciences—was the Human Genome Project, which, from its launch in 1990 to its culmination in 2003, successfully mapped the entire set of human DNA. With respect to the investigation of ongoing evolution, however, great difficulties have persisted until much more recently.

Detecting signs of evolutionary selection in human populations has historically proved difficult. Even in more recent decades, with our rapidly expanding body of genetic data, the nature of directional selection renders it difficult to identify. Perhaps the single biggest issue is the polygenic nature of many traits—that is to say, numerous key traits determining both appearance and lifestyle are determined by the contributions of multiple independent genes across many locations in the genome, rather than single, easily identifiable genes. This, in turn, means that meaningful changes of form and fitness may often be caused by a multitude of minor shifts across many locations, none of which are individually striking, and the totality of which can be exceedingly difficult to distinguish from the background “noise” of ordinary genetic drift across generations. 

However, work has been done in this area. Some traits are genetically simpler and, thus, easier to measure than others, and methods for studying polygenic complexes are advancing. A major study published in March 2026 is the largest and most thoroughgoing investigation of directional selection across human history to date. Looking at a dataset of over 15,000 West Eurasian people from whom DNA data could be extracted, and spanning a period of some 18,000 years, the study applied a novel methodology which has provided a hitherto-unmatched insight into the recent evolutionary history of our species (at least in one part of the world).

The study finds ample evidence of evolutionary selection across West Eurasian populations, often (though not always) in ways seemingly comporting with prior suspicions. Thus, we see a decline in darker skin tones and corresponding selection for those alleles associated with fairer skin, increasing selection for alleles correlated with higher intelligence, and for reduced body fat and waist circumference. All these changes may in fact be adaptive responses to the same lifestyle shift amongst ancient West Eurasians, from an existence of hunting and gathering towards one marked by sedentism and agriculture: as people settled, the lightening of their skin may have compensated for increasingly Vitamin D–poor diets, whilst greater intelligence would intuitively be favoured in complexifying societies. Even the aforementioned physiological changes may have been responses to the change from a hunting lifestyle: for decades, the thrifty gene hypothesis has been employed to explain many genetic propensities towards obesity, diabetes, and other metabolic issues as carry-overs from past adaptations that were useful in the long eras of the distant past when nutrition  was not so easy to come by nor so reliable in coming.