Abstract

The distribution of organisms in morphologic space is clumpy. Cats are like felids, dogs are like canids and snails are (mostly) like gastropods. But cats are not like dogs and snails are not like clams. This clumpy distribution of morphology has long posed one of the greatest challenges to evolutionary biologists. Does it represent the extinction and disappearance of a oncecontinuous distribution of morphologies, clades perched on the summits of persistent selective peaks ala Sewell Wright, or a primary signature of the evolutionary processes? And if the latter, what processes are responsible for generating it? Although often couched in discussions of the origin of higher taxa, such taxa are but proxies for this clumpy distribution, and ultimately the latter is the critical issue for macroevolution and for Stephen Jay Gould’s opus. Underneath all the controversies over whether species constitute individuals, whether speciation serves to divide intra-specific adaptation driven by natural selection from a set of inter- and supra-specific evolutionary processes, and over the impact of catastrophic mass extinctions on evolutionary trends, the fundamental issue is simply one of clumpiness (or, if you prefer, the inhomogeneous distribution of morphologies). Iurii Filipchenko, a Russian geneticist and the mentor of Theodosius Dobzhansky, introduced the term macroevolution in 1927 because he believed that the origin of the characters associated with higher taxa (those beyond the species level) required a different process of evolution. Filipchenko believed macroevolution was driven by cytoplasmic inheritance, but his general argument was consistent with other saltationists and macro-mutationists of the time, including the paleontologist Henry Fairfield Osborne and the geneticist Richard Goldschmidt. These evolutionary biologists shared the..