Tuesday, March 17, 2009

Evolution and development compared

The fact of shared developmental processes is a profound indicator of the importance of general principles, or logic, in the construction of organisms. The life sciences were transformed by the exciting realization, due to Darwin and Wallace, that complex life has gotten here by way of historical processes, and the discovery of genomes as the storehouse of accumulating information that makes that possible. But too great a focus on the evolutionary time scale, and hence on changes in DNA sequence over long time periods, tends to pull attention away from the means by which genomes operate in the here and now. Developmental processes are somewhat different from the processes of evolution, though all are based on general principles of life, which we'll describe in a later post. This table is a way in which we think these two aspects of life might be compared.

Evolution is about change in genomes over many generations, while development is about differential use of genes in the same genome in a single lifetime. Evolutionary change is open-ended and unpredictable while development is so predictable that a trout never spawns a frog -- or even a salmon, although of course each new organism is unique. Both kinds of change are contingent on what's here now, but the constraints on development depend on environmental triggers and gene usage signaled by a single genome.

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