Scientists have successfully documented a rare case of active adaptation in action.Snow voles, they say, are genetically decreasing body weight in response to selective pressure triggered by consecutive winters with early snowfall.

Researchers from the University of Zurich say the voles are in the process of adapting to early-snowfall winters with a genetic decrease in body weight because smaller voles are considered adult by the time weather extremes abate.

They deem this a genetic change spurred by natural selection.It is occurring, as any adaptive evolution would, to ensure the survival of the species' population.

Erik Postma led the research team at the university's department of evolutionary biology and environmental studies.The team studied snow vole populations at an altitude of about 6,500 feet in their natural, alpine habitat.

"Contrary to our expectations, they didn't get bigger," Postma said. "Instead, adaptive evolution pushed the voles to become smaller and lighter." They initially expected any adaptation to lean toward an increase in size based on the rationale that it would make them more capable of surviving and reproducing.

In lieu of this, though, "the voles whose genetic make-up led to a lower body weight were the fittest, especially in years when the first winter snow fell earlier than usual," Postma explained.

This marks a significant find in the field of biological evolution, exemplifying how natural selection effects change in savvier ways than researchers can predict in some cases.

Photo: Nick Moise/Flickr