developmental system drift - senecio7の日記

True JR & Haag ES 2001 Developmental system drift and flexibility in evolutionary trajectories. Evol Dev 3:109-119.

"developmental system drift" (DSD)
the term "drift" is clearly distinct from genetic drift
nevertheless is appropriate because, as with genetic drift, chance and not selection determines the details of how developmental systems change under DSD

advocates of the Classical view, following T. H. Morgan, emphasized the relative paucity of morphological variation within species, and argued that genes in populations were largely invariable and that the fittest "wild type" alleles dominated
Balance advocates, on the other hand, led by S. Chetverikov, predicted a large amount of hidden variation in populations
the development of molecular population genetics, starting in the 1960s, revealed that natural populations abound with molecular genetic variation
largely proving that the intuitions of the Balance advocates were correct
this debate has been largely abandoned
its most glaring unsolved problem now haunts evolutionary developmental biologists (e.g., Stern 2000)
how much and what kinds of variability in developmental systems are meaningful and available for natural selection to act upon?

significant phenotypic effects have been routinely demonstrated for non-protein-coding molecular polymorphisms
by necessity, these studies rely on examining effects in isogenic backgrounds
in nature, it is probable that no two genetic backgrounds in which an allele occurs are identical
recent work in both developmental and quantitative genetics has found epistatic interactions among genes to be of paramount importance in determining phenotypes
in light of the importance of genetic context in which mutants arise, current views of the importance of molecular variation may need to be substantially revised

through fixation of many epistatic alleles and the constant shuffling of genetic backgrounds, initially identical developmental systems become species-specific Rube Goldberg contraptions of a sort, with each independent lineage developing a unique set of expedient measures to deal with current adaptational needs