Punctuated equilibria in the 1970s: Stephen Jay Gould between biological improvement and irreducible hierarchy

In The Structure of Evolutionary Theory , Stephen Jay Gould observed that the theory of punctuated equilibria formed “the coordinating centerpiece” of his work in evolutionary biology. It occupied this position because it bridged several themes in Gould’s thought, including the necessity of understanding evolution in a hierarchical context and a critique of the adaptationist program in evolutionary biology. Yet this assessment concealed a historical puzzle. The puzzle arose from the fact that the Gould of “Eldredge and Gould (1972)” held several commitments that the older Gould did not. These included a preference for adaptationist explanations and, perhaps more surprising, a commitment to the central importance of “biological improvement” in the history of life. So, how did punctuated equilibria come to play a coordinating role within a view of evolution that differed starkly from the one Gould held in 1972? And why did it only begin to play this role after 1977? This article answers these questions, focusing on the aims of Gould’s early research program and its transformation in response to external stimuli. In so doing, it illuminates an important and frequently misunderstood episode in the history of paleobiology.