GOULD’S ODDESSY: FORM FOLLOWS FUNCTION, OR FORMER FUNCTION, AND ALL SPECIES ARE EQUAL (ESPECIALLY BACTERIA), BUT HISTORY IS TRUMPS

Early in his career, Stephen Jay Gould sought to quantify the forms of fossil shells and bones, to better understand their functions. Since form and function necessarily change with increasing size, this led him naturally to allometry, and hence to a major reassessment of the role of heterochrony in evolution. These studies led him to explore "laws of form" from a biomechanical point of view, focusing on the adaptive significance of changes in the shapes of snail and scallop shells, and of pelycosaur bones. He became fascinated, for a while, with the formal constraints of geometry so well articulated by D’Arcy Thompson. However, he came to mistrust aspects of these ideas in which he saw elements of vitalism and formalistic determinism.

Meanwhile, well-schooled in the precepts of allopatric speciation and Simpson’s Tempo and Mode, Niles Eldredge and Gould developed and energetically promoted the concept of ‘punctuated equilibrium.’ This led Gould to focus on the evolutionary mechanisms that gave rise to the actual history of life on Earth. Ultimately, species selection became the second of three tiers in Gould’s conceptual hierarchy of levels at which selection and sorting generate the large-scale patterns of evolution.

In Gould’s last, comprehensive account of his expansion of Darwinian evolutionary theory, constraints of form and function are not neglected, but they consistently play second fiddle to historical contingency. As causal factors, function determines what may be adaptive in the right circumstances, and constructional constraint prescribes what the organism can or cannot grow, as products of its development. These factors determine what can evolve and they explain why convergence is ubiquitous, but they cannot fully explain the "lovely puzzles" posed by the evolution of "actual organisms in real places." Gould preferred contingency to any sort of more general determinism, on ideological grounds. His evolutionary theory does not require that the effects of natural selection, speciation, or extinction must be unbiased in their directions. But, Gould’s humanity – his commitment to free will – did require this. It gave rise to a highly personal evolutionary synthesis that seeks primarily to explain those individual and collective properties of living organisms which record their historical origins.