A mutation accumulation assay reveals a broad capacity for rapid evolution of gene expression

An experiment in twelve different strains of Drosophila suggests that naturally occurring mutations generate a large amount of gene expression variation at a surprisingly rapid rate. After only 200 generations of allowing natural mutations (with weak or no ill effects) to accumulate, gene expression evolution was detected in 40% of all genes. That variation has the potential to fuel evolution, yet comparison of the observed evolutionary rates with differences between species suggests that natural variation is constrained by physical, developmental, or some other factors.