“Punctuated equilibrium,” Lin said, “is a theory proposed in 1972 by Niles Eldredge and Stephen Jay Gould. Before that time, evolutionary biologists had debated how new species developed. Most thought it happened gradually over time—what we call phyletic gradual evolution. But the fossil record doesn’t support that. It shows that when a species emerges, it is generally stable, with little genetic change, for long stretches of time. When evolution does occur, it happens rapidly—new species branch off in a relatively short period of time. On a geological scale, anyway.”
