Daily Archives: May 4, 2009

Innovations Sans Designer-Mimic

The other night, I asked, “What dynamics determine whether natural selection behaves as a trash man or a blind watchmaker?”

Let’s again consult Koonin, as he summarizes Michael Lynch’s non-adaptationist population-genetic theory of evolution of genomic complexity:

As already alluded to in the preceding section, the central tenet of the theory is that genetic changes leading to an increaseof complexity, such as gene duplications or intron insertions are slightly deleterious, and therefore can be fixed at an appreciable rate only when purifying selection in a population is weak. Therefore, given that the strength of purifying selection is proportional to the effective population size, substantial increase in the genomic complexity is possible only during population bottlenecks. Under this concept, genomic complexity is not, originally, adaptive but is brought about by neutral evolutionary processes when purifying selection is ineffective. In other words, complexification begins as a ‘genomic syndrome’ although complex features (spandrels) subsequently are co-opted for various functions and become subject to selection. By contrast, in highly successful, large populations, like those of many prokaryotes, purifying selection is so intense that no increase in genomic complexity is feasible, and indeed, genome contraction is more likely.

It sounds to me like the designer-mimic (and the trash man) is absent during population bottlenecks. In fact, feast your eyes on this observation from Koonin (emphasis added):

On the whole, the theoretical and empirical studies on the evolution of genomic complexity suggest that there is no trend for complexification in the history of life and that, when complexity does substantially increase, this occurs not as an adaptation but as a consequence of weak purifying selection, in itself, paradoxical as this might sound, a telltale sign of evolutionary failure.

In other words, if evolution can maneuver into a landscape where the blind watchmaker is not present, or severely restricted, then we can get some truly significant evolutionary transitions. It’s as if the front-loaded state is being unleashed.