Friday, December 15, 2006

The Extended Phenotype - Introductory Summary

-There is survival value in the "packaging of life into discrete units" called "vehicles" or organisms.

-We can speak of "adaptations as being 'for the benefit of' something, but that something is best not seen as the individual organism" but the "active, germ-line replicator" which are not selected directly, but by proxy.

-A behavior pattern "can be treated like an anatomical organ."

-A species or "group" is not the unit of selection, and gene selectionism is not genetic determinism.

Regarding the defining of what constitutes an adaptation, Dawkins first takes on the concept of extreme adapationism and identifies three proposed constrants on "perfection" (or optimal function) that he finds less persuasive:

-Neutral mutations, which are changes in polypeptide structure having no effect on enzymatic activity of the protein, and thus having no phenotypic effect at all.

(Biochemical controversy: Do all gene substitutions have phenotypic effects?)
(Adaptationist controversy: Is this phenothypic effect the result of natural selection?)
Though it is possible to a phenotypic effect to be selectively neutral, beware human subjectivity in these judgements. Genetic drift plus natural selection may result in more optimal function than just the effects of natural selection alone.

-Allometry, which is the disproportionate growth of a characteristic (such as a large head in small humans and in large ants).

-Pleiotropy, which is the possession by one gene of more than one phenotypic effect.

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