This chapter contains sections titled: The Domains of Microevolution and Macroevolution Changing Meanings of Macroevolution An Expanding Hierarchy of Selection Origins of Novelty Mass Extinctions Is Evolution Uniformitarian? Conclusions Postscript: Counterpoint References.

Have the large-scale evolutionary patterns illustrated by the fossil record been driven by fluctuations in environmental opportunity, by biotic factors, or by changes in the types of phenotypic variants available for evolutionary change? Since the Modern Synthesis most evolutionary biologists have maintained that microevolutionary processes carrying on over sufficient time will generate macroevolutionary patterns, with no need for other pattern-generating mechanisms such as punctuated equilibrium or species selection. This view was challenged by paleontologists in the 1970s with proposals that the (...) differential sorting and selection of species and clades, and the effects of biotic crises such as mass extinctions, were important extensions to traditional evolutionary theory. More recently those interested in macroevolution have debated the relative importance of abiotic and biotic factors in driving macroevolutionary patterns and have introduced comparative phylogenetic methods to analyze the rates of change in taxonomic diversity. Applying Peter Godfrey-Smith’s distinction between distributional explanations and explanations focusing on the origin of variation, most macroevolutionary studies have provided distributional explanations of macroevolutionary patterns. Comparative studies of developmental evolution, however, have implicated the origin of variants as a driving macroevolution force. In particular, the repatterning of gene regulatory networks provides new insights into the origins of developmental novelties. This raises the question of whether macroevolution has been pulled by the generation of environmental opportunity, or pushed by the introduction of new morphologies. The contrast between distributional and origination scenarios has implications for understanding evolutionary novelty and innovation and how macroevolutionary process may have evolved over time. (shrink)

Eric Davidson had a deep and abiding interest in the role developmental mechanisms played in generating evolutionary patterns documented in deep time, from the origin of the euechinoids to the processes responsible for the morphological architectures of major animal clades. Although not an evolutionary biologist, Davidson’s interests long preceded the current excitement over comparative evolutionary developmental biology. Here I discuss three aspects at the intersection between his research and evolutionary patterns in deep time: First, understanding the mechanisms of body plan (...) formation, particularly those associated with the early diversification of major metazoan clades. Second, a critique of early claims about ancestral metazoans based on the discoveries of highly conserved genes across bilaterian animals. Third, Davidson’s own involvement in paleontology through a collaborative study of the fossil embryos from the Ediacaran Doushantuo Formation in south China. (shrink)

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.. (shrink)