An evolutionary biologist at the University of Rochester has put forth a new theory on the genetic foundations of adaptation, the process whereby a species responds to a changing environment. H. Allen Orr suggests that, faced with environmental change, organisms can evolve through a mix of many minute genetic tweaks, a lesser number of moderate changes, and a few major mutations. The new idea runs counter to standard theory on evolutionary genetics, which holds that only the tiniest of genetic changes contribute to adaptation. The work is published in the August issue of Evolution, due out this month.
Orr's is the first new theory on the genetic architecture of adaptation since biologist R.A. Fisher's 1930 assertion that adaptation is solely the result of minor changes in genes -- a view that's come under fire over the last 15 years. Orr's new work is the most thorough attention given to the genetic basis of adaptation in decades, says Nick Barton, a noted evolutionary biologist at the University of Edinburgh in Scotland.
"Allen Orr gives an admirably thorough treatment, which is much more sophisticated than Fisher's brief argument," Barton says. "Overall, I think that Orr's paper will stimulate a good deal of theoretical and empirical work on what is a key question in evolution: what kind of genetic changes contribute to adaptation."
Adaptation, which can take thousands of years to complete, takes forms ranging from the subtle to the mammoth. An example of the process is a species of fruit fly transported to an isolated island in the Indian Ocean hundreds of thousands of years ago. Over the millennia, the tiny fly's isolation from other populations permitted so much genetic divergence -- enough even that the island species now subsists on a fruit that's toxic to all other species -- that it's now considered a distinct species, incapable of breeding with its ancient brethren.