Stephen Jay Gould was a prominent evolutionary biologist who argued against the prevailing view of gradualism in the 1970s and 80s. His arguments were based on empirical evidence and theoretical considerations and have had a significant impact on the field of evolutionary biology.
Gradualism is the view that evolution occurs through the gradual accumulation of small changes over long periods of time. This view was first articulated by Charles Darwin and has been the dominant view in evolutionary biology for more than a century. However, Gould argued that this view was based on a misinterpretation of the fossil record and ignored the importance of contingency and historical contingency in evolutionary change.
In his essay “Is a new and general theory of evolution emerging?” (1980), Gould argued that the fossil record showed a pattern of stasis punctuated by rapid bursts of evolutionary change. He suggested that species remain relatively stable over long periods of time, with occasional bursts of rapid speciation and extinction. He called this pattern “punctuated equilibrium” and argued that it was a better explanation of the fossil record than gradualism.
Gould’s arguments were based on the empirical evidence of the fossil record, which he claimed showed a pattern of long periods of stability interrupted by relatively short periods of rapid change. He also pointed out that this pattern was consistent with what we know about the processes of evolution, which are inherently contingent and unpredictable.
Gould argued that the traditional view of gradualism was based on a false dichotomy between stasis and change, and that the real picture was more complex. He suggested that evolutionary change was influenced by a variety of factors, including developmental constraints, historical contingency, and random events.
Gould’s arguments were controversial and have been the subject of much debate in the field of evolutionary biology. However, his ideas have had a significant impact on the way we think about evolution and the role of contingency in the history of life.
Here are some quotes from Gould’s works that summarize his arguments regarding gradualism:
“Gradualism is not a necessary conclusion of Darwinism, but a metaphysical stance that Darwin adopted to make his system more palatable to Victorian sensibilities. It is the modern synthesis, rather than Darwinism per se, that has wedded gradualism to the theory of natural selection.” (Gould, “Is a new and general theory of evolution emerging?” 1980)
“The history of life is not a tale of linear progress but a complex, multilinear and reticulate tree. The main lines of descent are interspersed by numerous side branches, and the order of arrangement is determined by the contingent events of extinction and speciation.” (Gould, “Wonderful Life: The Burgess Shale and the Nature of History,” 1989)
“Darwinism must be stretched and enriched, but not abandoned. The theory of evolution by natural selection is still the only one capable of explaining the complexity and diversity of life, and the best framework for future research.” (Gould, “The Structure of Evolutionary Theory,” 2002)
Gould, S. J. (1980). Is a new and general theory of evolution emerging? Paleobiology, 6(1), 119-130.
Gould, S. J. (1989). Wonderful life: The Burgess Shale and the nature of history. W. W. Norton & Company.
Gould, S. J. (2002). The structure of evolutionary theory. Harvard University Press.