Does Gene Expression Evolve?
“Mutation is the ultimate source of biological diversity because it generates the variation that fuels evolution,” wrote four scientists in Nature November 10.1 Conventionally, theorists have focused on gene mutations for that fuel; what about mutations to gene expression? That’s what they set out to discover.
One would think that positive natural selection would drive gene expression. If nothing else, neutral mutations would be expected to accumulate over time. Looking at fruit flies and worms, however, they found less than anticipated. This was a surprise to them, “suggesting that stabilizing selection has a larger role than drift in shaping the evolution of gene expression.” Stabilizing selection is a conservative effect. A perturbation in one part of the gene expression network might be counterbalanced by another, such that the overall developmental pattern is unchanged. This leads to phenotypic stability called canalization. Though their title and conclusion hyped plasticity, they discovered stability:
In summary, D. melanogaster has a broad mutational capacity for changes in gene expression, in both magnitude and genomic extent, that could potentially provide ample raw material for evolutionary diversification. However, although they vary among closely related species, gene expression patterns are relatively stable. In Caenorhabditis elegans, genetic variances of gene expression are likewise much less than the neutral expectation. The convergence of this observation in two groups of organisms that diverged in the Precambrian and have different reproductive and life-history strategies indicates that stabilizing selection and structural processes, including canalization, physical and developmental constraints, and correlated responses, govern gene expression evolution. (Emphasis added in all quotes.)
1Scott A. Rifkin, David Houle, Junhyong Kim and Kevin P. White, “A mutation accumulation assay reveals a broad capacity for rapid evolution of gene expression,” Nature 438, 220-223 (10 November 2005) | doi:10.1038/nature04114
Anyone see evolution here? Stabilizing selection is not the kind Darwin wanted. It’s like those displays in appliance stores where a beach ball is suspended above a blower. The ball spins and gyrates, but the higher pressure around the flowing air holds the ball in place. The evidence suggests that organisms are robust against perturbations in gene expression. Two similar species of fruitflies and worms maintained very stable patterns of gene expression despite these evolutionists’ claim the creatures diverged in the Precambrian. That’s a lot of un-evolution for 200 million years. The rest of the bluff about “mutational capacity” providing “raw material” for evolution was just verbal turbulence flowing past a Darwinian beach ball suspended in mid-air.