Stephen Jay Gould

Stephen Jay Gould (1941–2002) was a paleontologist, evolutionary biologist, and essayist who did more than almost anyone in the twentieth century to clarify what evolution actually is—and what it is not. It is not a ladder, not a march of progress, not a predetermined ascent from primitive to advanced. It is a copiously branching bush, continually pruned by extinction, with no main trunk and no predetermined summit. The organisms that dominate today are not the best organisms; they are the organisms that happened to survive the specific contingent events—asteroid impacts, climate shifts, the accidental survival of one predator over another—that characterized their moment. Replay the tape of life, Gould argued, and you get a different world: humans would almost certainly not evolve, because the specific sequence of contingent events that produced us is unrepeatable. This thesis, which he spent his career elaborating against resistance from adaptationist colleagues who saw natural selection as an