Macroevolution, pattern and process

In this text, the author addresses, from a palaeobiologist's perspective, the question of whether punctuated equilibria - the view, popularized by Stephen Jay Gould among others, that species remain evolutionarily static for long periods of time, with substantial genetic changes and the development of new adaptive strategies occurring only during speciation, or gradualism - the view that large-scale changes result from continual and successive small-scale changes, offers the best account of the history of life. Coming down on the side of those who favour the model of punctuated equilibria, Stanley argues that only quantum speciation (rapid and radically divergent), can explain the story of life revealed in the fossil record; macroevolution, he contends, cannot be attributed to microevolutionary forces such as mutation, genetic drift and natural selection. Instead, he posits a series of processes, including species selection, phyletic drift and directed speciation, to accounnt for large-scale patterns.