Evolving a new function via gene duplication and divergence

Bjørn Østman at Pleiotropy describes new research in Science that shows how duplicated genes can evolve to perform new functions. It presents

… a new model/mechanism by which duplicated genes can retain the selection pressure to not succumb to deleterious mutations. They call it the innovation-amplification-divergene model (IAD).

Basically,

IAD works like this: A gene initially has one function only (A). Then some genetic changes makes it also have a new function, b, which at first is not of too great importance. Then some environmental change favors the gene variants with the minor b-function (the innovation stage). This is then followed by duplication of the gene, such that there are now more than one copy that carries out A and b (the amplification stage). At this stage there is selection for more b, and at some point genetic changes in one of the copies results in a gene that is better at the new function, B. At this point, selection for the genes that do both A and b is relaxed, because the new gene (blue) carries out the new function. The original gene then loses the b function, and we are left with two distinct genes.

Michael Behe, of course, scoffs. Because the researchers did some manipulations that created conditions favorable to the evolution of the new function, Behe claims that

Needless to say, this ain’t how unaided nature works – unless nature is guiding events toward a goal.

Shucks. I guess every experimental manipulation ever performed has been an invalid method of studying some process. But as a PT crew member pointed out on the back channel, “this kind of shit happens all the time in nature.” See, for example, Gene duplication and the adaptive evolution of a classic genetic switch or Escape from adaptive conflict after duplication in an anthocyanin pathway gene.