The Scientist has published a current essay I wrote about the evidence for recent and ongoing natural selection in humans: “Humans Never Stopped Evolving”.
Natural selection is tricky to catch in action. As Darwin put it, “A grain in the balance will determine which individual shall live and which shall die.” The grain in the balance—the slightly increased chance that organisms carrying one gene variant will fail in the struggle for existence—is the cost of selection. It is almost invisible, only becoming statistically evident when viewed across thousands of individuals, who may display only subtle differences in the affected character.
In the human population, the toll of natural selection is hidden within millions of deaths and births around the world every year. Everyone dies, many tragically young. And while obvious patterns sometimes emerge from early deaths—certain diseases, traffic accidents, drug overdoses—these are often challenging to connect to the action of genes. Likewise, only by comparing the genes of parents with those of childless people, and the genes of large families with those of small families, can we begin to understand how natural selection is acting on births.
I present a few of the classic examples, including lactase persistence and the Duffy blood group. Then I turn to consider the evidence of selection on continuous traits, much of which has just been emerging during the past couple of years. This is an exciting area right now, and there is much more to say about it.
I also struck a deal to make this article available via a Creative Commons license, and I will be reposting it after a couple of weeks.