Saturday, 5 February 2011

Evolved genetic guesses

Once it is recognized that not all mutations are random mistakes, the way one sees the relationship between physiological and developmental adaptation and evolutionary adaptation begins to change. We are used to thinking of them as very different: physiological and developmental changes involve instruction - what happens in cell or organisms is controlled by internal or external regulatory signals; evolutionary changes involve selection - some heritable variants are preferred to others. In the jargon of philosophers of biology, the physiological and developmental processes that underlie a phenotype are "proximate causes", while evolutionary processes - natural selection and whatever else has constructed the phenotype during evolutionary history - are "ultimate causes".

Yet, if the generation of some heritable variation is under physiological or developmental control, how distinct are the two types of causes? Seeing evolution purely in terms of selection acting on randomly generated variation is wrong, because it involves instructive processes too. As we see it, the dichotomy between physiology/development and evolution, and between proximate and ultimate causes, it is not as absolute as we have been led to believe. They grade into one another. At one extreme there are purely selective processes, acting on chance variation, while at the other there are purely instructive processes,which are totally physiological or developmental and do not involve any selection. Between these extremes we find the majority of processes in the real world, which are to varying degrees both instructive and selective. Some developmental changes, such as those occurring during the development of the immune system, also involve selection, whereas some evolutionary changes, particularly in bacteria and plants, may have instructive components. In other words, Darwiniam evolution can include Lamarckian processes, because the heritable variation on which selection acts is not entirely blind to function; some of it is induced or "acquired" in response to the conditions of life.

From: Evolution in four dimensions by Eva jablonka and Marion J. Lamb

No comments: