Heterochrony in Evolution
In Utopia the creation of traits in response to changing environmental conditions could occur ex nihilo,with no restrictions based on what had occurred in the past. There would be no discernible patterns in the appearance of new characters. But life is not like that. The paleontological and neontological records teem with evolutionary patterns, many repeated in disparate groups. Biological evolution is strongly constrained by what structures exist at each step of the evolutionary journey. Rather than new structures being created from scratch by genetic mutations, evolution involves “tinkering” with preexisting parts (Jacob, 1977). Furthermore, this tinkering needs to be carried out while the “machine is running” (Frazzetta, 1975), for the organism must remain viable even while these changes are occurring. Consequently, structural changes need to be made as rapidly as possible and to as few working components as possible. When complete, the organism must work as a fully functioning, integrated unit.
KeywordsFossil Record Environmental Gradient Predation Pressure Adaptive Threshold Juvenile Phase
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