I am acquainted with Steve Jones, professor of zoology at University College, London. He’s a lovely science writer and has talked a lot of sense. But I have never understood why he is so implacably opposed to the idea that Homo sapiens continues to evolve. He sees that there is very little genetic variation across modern human groups – far less than other primate species – and assumes there is therefore little for evolution to bite on. Yet there are 7 billion genomes out there, pole to pole, at the moment, and that number continues to grow. And there are huge differentials in the efficacy of modern medicine, quality of environment, life expectancy, differential reproductive success, exposure to toxins and pathogens, all resulting in differences in frequency of gene variants in human populations. And indeed, the explosion of human culture exerts its own selection pressures. I much prefer the approach of John Hawks, professor of anthropology at the University of Wisconsin-Madison, who believes humans never stopped evolving and has just written this essay in The Scientist, laying out his stall for the view that humans continue to evolve.

Hawks cites work we all know about from Steve Stearns and his colleagues on the Framingham study, and recent work by Jonathan Beauchamp, at Harvard, who compared known gene variants with lifetime reproductive success in a large number of people enrolled in the Health and Retirement Study. He then brings in the evolution of Duffy blood types, glucose-6-phosphate dehydrogenase, and lactase persistence; skin colour and height. At the end of his essay, in a section titled “Evolving Into The Future” Hawks makes his counter to those geneticists (like Jones) who believe that human evolution has ground to a halt over the last 100,000 years or so: “If there is one common theme in all this recent selection, it is that much of the human diversity we see around us today arose very recently. More than 90 percent of the heritage of every living human comes from sub-Saharan Africa sometime around 100,000 years ago. Fifteen years ago, many geneticists saw this recent common ancestry as evidence that human evolution had mostly drawn to a close. After diverging from our common chimpanzee and bonobo ancestors some 7 million years ago, hominins underwent massive changes in body size, diet, behavior, and brain size. Huge evolutionary innovations marked the beginning of upright walking, tool use, culture, and language. And those changes all happened before 100,000 years ago.

With such a dramatic picture from the fossil record, it is understandable that many scientists assumed that the final phases of human prehistory were fairly boring, at least from the Darwinian point of view. Across most of the genome, humans everywhere in the world are very similar to one another, much more so than to chimpanzees or most other kinds of primates. Modern humans vary profoundly in cultures and languages, but those differences are mostly learned, not coded in our genes.

Nevertheless, humans across the globe have been living under very different selective pressures since our sub-Saharan roots. And, in fact, the cultural differences that have emerged appear to have accelerated some kinds of evolutionary changes. The domestication of animals led to the invention of dairying, for example, a new dietary niche in which lactase persistence provided a huge advantage. Clearing tropical lands for planting domesticated crops and keeping water in pots changed human ecology in more-disturbing ways, making new habitats for mosquito species that afflict human populations with yellow fever and malaria and spurring protective changes in red blood cell morphology. Moving into new ecosystems also demanded new adaptations from the growing human population, from lighter pigmentation at high latitudes to maintain vitamin D production to improved oxygen metabolism in peoples living at high altitude.

Natural selection is fickle. Behavior that ensured survival in our ancestors’ environment may not be as advantageous under modern conditions. New evidence of how the human genome has changed over the last several thousand years points to a series of massive critical evolutionary changes, setting some aspects of our biology clearly apart from that of our forebears. And we are no doubt continuing to evolve today.”