  Two giants of evolutionary theory, Sewall Wright and R. A. Fisher, fought
bitterly for over thirty years. The Wright-Fisher controversy forms a
cornerstone of the history and philosophy of biology. I argue that the standard
interpretations of the Wright-Fisher controversy do not accurately represent
the ideas and arguments of these two key historical figures. The usual account
contrasts the major slogans attached to each name: Wright's adaptive landscape
and shifting balance theory of evolution versus Fisher's fundamental theorem of
natural selection. These alternative theories are in fact incommensurable.
Wright's theory is a detailed dynamical model of evolutionary change in actual
populations. Fisher's theory is an abstract invariance and conservation law
that, like all physical laws, captures essential features of a system but does
not account for all aspects of dynamics in real examples. This key contrast
between embodied theories of real cases and abstract laws is missing from prior
analyses of Wright versus Fisher. They never argued about this contrast.
Instead, the issue at stake in their arguments concerned the actual dynamics of
real populations. Both agreed that fluctuations of nonadditive (epistatic) gene
combinations play a central role in evolution. Wright emphasized stochastic
fluctuations of gene combinations in small, isolated populations. By contrast,
Fisher believed that fluctuating selection in large populations was the main
cause of fluctuation in nonadditive gene combinations. Close reading shows that
widely cited views attributed to Fisher mostly come from what Wright said about
Fisher, whereas Fisher's own writings clearly do not support such views.
