Has human evolution slowed down – or even stopped – its evolution with the advent of civilization and medicine? A genetic study of unprecedented scale, recently published in the journal Nature and relayed by Live Science, unravels this preconceived idea. By analyzing the DNA of 16,000 individuals, ancient and modern, researchers have discovered that we are always changing.
The observation is clear. Natural selection has acted on nearly 500 genetic variants over the last ten millennia in Western Eurasia. This is not a simple statistical drift, but a real and targeted adaptation. For Ali Akbari, researcher at Harvard University and first author of the study, the explanation is simple: “Human evolution has not slowed down; we just lacked the signals to see it.” Thanks to new statistical tools, scientists can now detect tiny but consistent changes where we once saw only genetic noise.
One of the most visible aspects of this evolution concerns our physical appearance. The study reveals that natural selection favored genes linked to light skin, an adaptation well known to optimize vitamin D production in less sunny latitudes. More surprisingly, the frequency of genes responsible for red hair has skyrocketed. If scientists are still struggling to explain the direct evolutionary advantage that redheads would have, they suggest that this trait could be linked to other, more crucial adaptations that would have traveled with it in our genetic code.
The evolution would also tend towards less baldness. Natural selection seems to have favored men who kept their hair longer. The study also affirms that we have evolved to better resist historical scourges such as leprosy or HIV, while reducing our vulnerability to certain inflammatory diseases such as rheumatoid arthritis.
Our genome is a veritable history book of past epidemics. Researchers noticed that certain vulnerability genes, such as those linked to tuberculosis, increased in frequency before suddenly dropping around 3,500 years ago. Same scenario for multiple sclerosis, the susceptibility of which increased before falling again two millennia ago. This genetic roller coaster proves that our body adapts in real time to the new pathogens it encounters.
The real superpower: adaptation
What makes this study fascinating is that it shows to what extent humans are plastic creatures, capable of adapting to their environment. We don’t just endure it, we biologically adjust to it at a speed that we had not suspected. “What is likely to differ across regions is not whether selection has occurred or not, but how local environments and cultural changes have shaped it”underlines Ali Akbari. Clearly, our food, our climate and our urban lifestyles are the new engines of our DNA.
Scientists do not intend to stop there. After Eurasia, they are now turning their attention to East Asia and other continents. Initial results suggest that similar patterns of rapid selection exist around the world. This global quest will help understand how each population developed its own biological “shields” in the face of the challenges of its unique history.
Far from being the finished outcome of a long process, humans are a link in a chain that continues to be forged. Each generation carries with it small corrections, subtle adjustments that allow us to survive in a world that is changing more and more quickly.
Our descendants will surely carry within them the genetic traces of our current way of life. Whether it is our resistance to new diseases or our adaptation to modern diets or pollution, the adventure of human evolution is still being written today.
