Day: December 18, 2008

Occasionally I’ll read articles in newspapers or magazines speculating that humans are no longer subject to natural selection and just have to shake my head. Fortunately, Scientific American has a nice overview of the current state of thinking about human evolution that dispels that “we’re no longer evolving nonsense.” In fact, it appears to be just the opposite,

But DNA techniques, which probe genomes both present and past, have unleashed a revolution in studying evolution; they tell a different story. Not only has Homo sapiens been doing some major genetic reshuffling since our species formed, but the rate of human evolution may, if anything, have increased. In common with other organisms, we underwent the most dramatic changes to our body shape when our species first appeared, but we continue to show genetically induced changes to our physiology and perhaps to our behavior as well. Until fairly recently in our history, human races in various parts of the world were becoming more rather than less distinct. Even today the conditions of modern life could be driving changes to genes for certain behavioral traits.

. . .

But that turns out not to be the case. In a study published a year ago Henry C. Harpending of the University of Utah, John Hawks of the University of Wisconsin–Madison and their colleagues analyzed data from the international haplotype map of the human genome [see “Traces of a Distant Past,” by Gary Stix; Scientific American, July 2008]. They focused on genetic markers in 270 people from four groups: Han Chinese, Japanese, Yoruba and northern Europeans. They found that at least 7 percent of human genes underwent evolution as recently as 5,000 years ago. Much of the change involved adaptations to particular environments, both natural and human-shaped. For example, few people in China and Africa can digest fresh milk into adulthood, whereas almost everyone in Sweden and Denmark can. This ability presumably arose as an adaptation to dairy farming.

Another study by Pardis C. Sabeti of Harvard University and her colleagues used huge data sets of genetic variation to look for signs of natural selection across the human genome. More than 300 regions on the genome showed evidence of recent changes that improved people’s chance of surviving and reproducing. Examples included resistance to one of Africa’s great scourges, the virus causing Lassa fever; partial resistance to other diseases, such as malaria, among some African populations; changes in skin pigmentation and development of hair follicles among Asians; and the evolution of lighter skin and blue eyes in northern Europe.

Harpending and Hawks’s team estimated that over the past 10,000 years humans have evolved as much as 100 times faster than at any other time since the split of the earliest hominid from the ancestors of modern chimpanzees. The team attributed the quickening pace to the variety of environments humans moved into and the changes in living conditions brought about by agriculture and cities. It was not farming per se or the changes in the landscape that conversion of wild habitat to tamed fields brought about but the often lethal combination of poor sanitation, novel diet and emerging diseases (from other humans as well as domesticated animals). Although some researchers have expressed reservations about these estimates, the basic point seems clear: humans are first-class evolvers.

The article goes on to provide a simple gloss over different possibilities for human evolution including extinction, stasis, and even self-directed evolution (transhumanism FTW).

It seems odd to see stasis as an option. In the short term, certainly we can arrange things so humanity remains relatively as it is now if we really wanted too, but only if we maintain the same environment and clearly that is simply not an option. Human culture changes the environment which then fuels further changes in human culture. There’s very little about the last 50,000 years of humanity’s existence which could in any way, shape or form be described as static.

Running in place is simply not an option for homo sapiens.