Natural Selection Cuts Broad Swath Through Fruit Fly Genome

This article from a year ago describes an experiment on fruit flies that supports the hypothesis that evolution and adaptation is driven by multiple gene changes. Scientists at the University of California, Irvine, bred fruit flies through 600 generations and chose the ones that hatched first to be the parents of the next generation; such selection led to a 20 percent decrease in the time needed for hatching. After studying the genomes of hundreds of these flies, they concluded that this evolutionary change was driven by a soft sweep (where the trait is affected by many genes) rather than a hard sweep (where a single mutation is spread through the population). Following this view, Jonathan Pritchard of the University of Chicago explained that in human evolution, there seems to be many more soft sweeps than hard sweeps in adapting to new environments. This fruit fly experiment shows that such a mechanism is indeed possible for driving evolution.