Punctuated Equilibrium and Macroevolution

Abstract

Hardened Darwinism is the view that the history of life is explained by forces operating on populations of organisms, or perhaps, on their genes. Large scale events and processes are no more than an aggregation of the fate of individual organisms. This story has received some rough treatment in the literature lately, for hierarchical views of evolutionary theory are currently popular. Eldredge, Gould and Stanley¹, to name only three, are on the record in urging that there are robust macroevolutionary phenomena, phenomena not captured generation by generation change in gene frequency. Three large scale patterns are most on people’s minds. One is mass extinction. Mass extinctions, its been alleged, are regular and intense. Most importantly, surviving mass extinction is mostly chance; it is not determined by an organism’s suite of adaptations. If so, the shape of the tree of life is determined not by the relative fitness of its various twigs, but by their proximity to an extrinsic, perhaps even extraterrestrial, pruner. A second is Gould’s most recent preoccupation, the “cone of decreasing diversity”. The theme of his 1989 is his idea that life reached its maximal diversity at the Cambrian explosion; diversity has declined since. On Gould’s view, natural selection played no central role in either the establishment of that diversity or its decline².