We are still evolving

A recent paper shows how human evolution has accelerated

I decided to take a short break from my intended series of essays exploring new ideas because of a recent paper by Akbari and colleagues that was published in the journal Nature in April this year (https://doi.org/10.1038/s41586-026-10358-1). Contrary to wide-spread beliefs, Akbari and colleagues’ work shows that our species is still subject to evolution through natural selection. In fact, selection appears to have accelerated over the last 10,000 years. To explain why I thought that this work is worthwhile writing about, I need to go back to that year I spent at the institute I mentioned in my previous post, What is nature.

One of the many interesting initiatives at the institute at which I resided was the so-called Three Cultures Forum. The idea was to bring people together from three different disciplines to discuss a particular topic from their discipline-specific angle, the three cultures. For better or for worse I suggested human ancestry as a topic, exploring the extent to which we can find genetic differences among human populations. I suggested the topic because of a paper by Bergström and colleagues that had been published in the journal Science in 2020, the year I spent at the institute (10.1126/science.aay5012). In it the authors trawled through 929 human genomes collected as part of the Human Genome Project, representing people from across the globe, and discovered that modern humans do not comprise one interbreeding population. Instead, one can identify genetic differences that coincide with geographical differences. In other words, the indigenous people from Australia can, on average, be distinguished genetically from indigenous people from Africa. The differences are small because we all come from the same population that originated in Africa about 300,000 years ago. In evolutionary time, 300,000 years is nothing. But, I argued, the differences are real and explain why we can, in general, guess one’s ancestry.

To my surprise and dismay, the other scientist who participated in the discussion used the same data as I, from Bergström and colleagues’ paper, to conclude that there is nothing to see. While there may be incy wincy tiny differences, he claimed, these differences are of no significance. I strongly suspect that his conclusion had more to do with political sensitivity than with science, so defeating the whole purpose of the Three Cultures Forum.

With my experience with the Three Cultures Forum in mind, I read Akbari and colleagues’ work with interest. They used ancient DNA from 15,836 West Eurasians spanning 10,000 years and showed that hundreds of variants have undergone strong directional selection. ‘Variants’ in this study refers to specific DNA differences in particular positions in the genome. By analysing millions of such DNA differences across the 15,836 individuals sampled, they were able to determine if the frequency of each variant changed over time in a non-random, directional way. If a particular DNA change becomes more common across generations, then that is evidence for that variant to be under directional selection. And that indicates that the variant is selected for because it conveys an advantage to the individual that carries that particular DNA sequence.

The study found that many hundreds of variants have undergone directional selection during the Holocene, the epoch that started about 11,700 years ago. The Holocene marks the end of the last major ice age and the start of a warmer, stable interglacial climate. That warmer and stable climate allowed the development of agriculture. And, as the saying goes, nothing has ever been the same. Agriculture was arguably the most single transformative event in human history, triggering a domino effect that completely restructured human society. It is that domino effect that Akbari and colleagues revealed in our genomes.

Natural selection is an interplay between an individual’s genetic make-up and its environment. A variant that conveys a benefit when living at high altitudes, say, is of little use at sea level. (Fun fact: Tibetans carry several genetic variants that allows them to live at high altitudes and these genes most likely came from their ancestors interbreeding with Denisovans.) It is therefore no surprise, at least not to me, that the careful study by Akbari and colleagues finds that different human populations show differences in the variants that they carry. In other words, as in the study my colleague dismissed, different geographical populations of humans show differences in their genetic make-up, which, to some extent, is the result of natural selection fine-tuning genetic variants suitable to a particular environment.

Genetic differences among human populations does not imply that we can determine from an individual’s genome where they came from. The example I used in my Three Cultures Forum argument was that of height. My ancestry is the Netherlands, the land of giants. The height of an average Dutch female is 170 cm (5 feet and 7 inches). At 153 cm (5.02 feet and 0.24 inches) one would not pick me as being Dutch, based on my height. But that doesn’t alter the fact that as a group, Dutch women are very tall. Similarly, while we cannot look at my genome and determine that my ancestry lies in land won from the sea, looking at the genomes of all Dutch people will reveal particular genetic variants not found in Africa. Many Europeans carry bits of DNA inherited from our ancestors’ dalliances with Neanderthals which turned out to be very useful in dealing with cold. Those bits of DNA cannot be found in people whose ancestors never left Africa because they never encountered our cousins.

The other two disciplines participating in the Three Cultures Forum discussing human ancestry came from history and sociology. Both argued against there being differences among human populations. Their main argument was centred around atrocities inflicted on human populations often justified using malign, or at the very least misguided, ‘science’. Because of past crimes and evil policies centred around a construed idea of human differences, they argued, we have to steer away from anything that can divide us. It seems that my fellow scientist felt the same. But in doing so he did science a disservice. If our aim is to re-establish the general public’s trust in science, then we, scientists, need to be able to hold honest discussions about scientific findings and only discredit work based on scientific validity, not political sensitivity.