Scientists have two ways to approach the question of current evolution, said Yale biologist Stephen Stearns. One is to compare DNA among lots of people.
DNA can show "signatures" of recent evolution, because at first, new advantageous mutations take big chunks of other DNA with them as they pass from parents to children. Over time, those chunks of DNA break apart and the advantageous genes can pass through generations less encumbered. The size of that genetic entourage works as a kind of molecular clock - the bigger it is, the more recently a new mutation appeared.
Comparing DNA samples from diverse ethnic groups has shown that new genetic mutations spreading in the last few thousand years are changing the way some people digest food, grow hair, store fat, and fight disease.
But these studies examine only a long time frame - evolution over the last few thousand years.
Another way to detect current evolution is to examine inheritance patterns of specific traits, a technique that's being used to study evolution over the last 150 years. That's when modern medicine and global travel became widespread, and, some say, drastically altered the course of human evolution. Some scientists have even argued that these factors are halting evolution's course for our species.
One such study, led by Case Western Reserve University anthropologist Cynthia Beall, showed that mountain dwellers in Tibet are being selected for better tolerance to their thin-air environment.
She found some Tibetans had much greater oxygen-carrying capacity in their blood than others. This trait ran in some families, she said, in a way that suggested it was tied to a genetic variant.
