Repression and loss of gene expression outpaces activation and gain in recently duplicated fly genes.

Evolutionists widely acknowledge that regulatory genetic changes are of paramount importance for morphological and genomic evolution. Nevertheless, mechanistic complexity and a paucity of data from nonmodel organisms have prevented testing and quantifying universal hypotheses about the macroevolution of gene regulatory mechanisms. Here, we use a phylogenetic approach to provide a quantitative demonstration of a previously hypothesized trend, whereby the evolutionary rate of repression or loss of gene expression regions is significantly higher than the rate of activation or gain. Such a trend is expected based on case studies in regulatory evolution and under models of molecular evolution where duplicated genes lose duplicated expression patterns in a complementary fashion. The trend is important because repression of gene expression is a hypothesized mechanism for the origin of evolutionarily novel morphologies through specialization.