The Quickening

Right around the holidays I always like to read a news story about science and evolution, because it tempers all the hooey about miracle virgin births and flying reindeer.

Anthropologist Henry Harpending and colleagues are inadvertently disproving the assertion of science fiction writers who've suggested a future Earth populated by a blend of all races into a common human form.

"Our species is not static," Harpending said, noting the reverse seems to be happening as people are evolving at a more rapid pace than even the distant past. Looking at the DNA of humans and of chimpanzees, researchers believe if evolution had been proceeding steadily at the current rate since humans and chimps separated 6 million years ago there should be 160 times more differences than the researchers found. The explanation? Human evolution had been slower in the past.

"Rapid population growth has been coupled with vast changes in cultures and ecology, creating new opportunities for adaptation," the study says. "The past 10,000 years have seen rapid skeletal and dental evolution in human populations, as well as the appearance of many new genetic responses to diet and disease."

Most anthropologists agree that humans first evolved in Africa and then spread to other areas, and the lighter skin color of Europeans and Asians is generally attributed to selection to allow more absorption of vitamin D in colder climate where there is less sun. As the human population increased from millions to billions in the last 10,000 years, the rate of evolution accelerated because due to new environments, and with a larger population, more mutations occurred.

In another example, the researchers noted that in China and most of Africa, few people can digest fresh milk into adulthood. Yet in Sweden and Denmark, the gene that makes the milk-digesting enzyme remains active, so almost everyone can drink fresh milk, explaining why dairy farming is more common in Europe than in the Mediterranean and Africa, Harpending says.

The archaeological record also shows that humans increasingly divided themselves into distinct cultures and migrating groups — factors that seem to play only a small role in their analysis. Dividing the human population into finer units and their movement into new regions — the Arctic, Oceania, tropical forests, just to name some — may have also forced quicker adaptive evolution in our species. Two years ago, Harpending and Gregory Cochran published a study arguing that above-average intelligence in Ashkenazi Jews — those of northern European heritage — resulted from natural selection in medieval Europe, where they were pressured into jobs as financiers, traders, managers and tax collectors. Those who were smarter succeeded, grew wealthy and had bigger families to pass on their genes, they suggested. That evolution also is linked to genetic diseases such as Tay-Sachs and Gaucher in Jews.

Me, smarter? Sure, I'll risk some Tay-Sachs just to prove a point.