Monday, November 10, 2008

Facilitated Variation: How the genetic code hedges its bets on a variable environment

Haven't had the chance to look very closely at the details, but this paper looks very interesting. Evolution thrives on variation, and according to them, the genomes of organisms can accumulate a sort of stored memory of past adaptation to varying environments that as they say "makes it more likely that random genetic changes will result in organisms with novel shapes that can survive."

Facilitated Variation: How Evolution Learns from Past Environments To Generalize to New Environments
Merav Parter, Nadav Kashtan, Uri Alon
PLoS Comput Biol 4(11): e1000206.
Abstract: One of the striking features of evolution is the appearance of novel structures in organisms. Recently, Kirschner and Gerhart have integrated discoveries in evolution, genetics, and developmental biology to form a theory of facilitated variation (FV). The key observation is that organisms are designed such that random genetic changes are channeled in phenotypic directions that are potentially useful. An open question is how FV spontaneously emerges during evolution. Here, we address this by means of computer simulations of two well-studied model systems, logic circuits and RNA secondary structure. We find that evolution of FV is enhanced in environments that change from time to time in a systematic way: the varying environments are made of the same set of subgoals but in different combinations. We find that organisms that evolve under such varying goals not only remember their history but also generalize to future environments, exhibiting high adaptability to novel goals. Rapid adaptation is seen to goals composed of the same subgoals in novel combinations, and to goals where one of the subgoals was never seen in the history of the organism. The mechanisms for such enhanced generation of novelty (generalization) are analyzed, as is the way that organisms store information in their genomes about their past environments. Elements of facilitated variation theory, such as weak regulatory linkage, modularity, and reduced pleiotropy of mutations, evolve spontaneously under these conditions. Thus, environments that change in a systematic, modular fashion seem to promote facilitated variation and allow evolution to generalize to novel conditions.

1 comment:

Charles Kennett (industrial biologist) said...

I didn't read the article that you posted here, but I just got done reading Kirschner and Gehart's book the Plausibility of Life(2003?). Here they go into faciliated variation in detail. I think that each of their separate ideas have interesting points, but I'm still not sure how exactly that somatic physiological adaptations can affect germ-line cells and end up potential adaptations in progeny (although I am going to reread the results of experiments on Drosophila in which heat shock adaptations were passed down for allegedly 40 generations without heat shock). I'm an old suscriber to Darwin/Weismann/Mayr positions, and am skeptical of alleged post-Synthesis reorganizations of evolutionary theory, including Gould's Punctuated equillibrium and his belief in heirarchical selection. As a student you should read very carefully such claims, for the extraordinary ones require extraordinary evidence.

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