Nature Steers a Predictable Course

Some evolutionary theorists have argued that drift, random gene changes that accumulate over time, underlies the evolution of new species. If so, evolution9s course would be unpredictable and unlikely to be repeated. But results reported in this issue show that it can be repeated in similar environments, findings indicating that natural selection is as important as Darwin had thought, often overriding the randomness of genetic drift. On page 308, researchers report that European fruit flies introduced in North America about 20 years ago have evolved larger wings over their south-to-north range, a change that parallels what happened to this species in Europe. And on page 306, another group reports that a stickleback fish living in three isolated lakes on British Columbia9s Pacific coast has formed the same two species in all three lakes.