Macroevolution

Macroevolution, or trans-specific evolution, refers to two different things in the literature on evolution. In discussions of phylogeny, it means phylogenetic branching pattern, or trends, seen at relatively high taxonomic levels (e.g., Stanley, 1979; Brooks and McLennan, 1991; Sober, 1993)—”any patterns that transcend species boundaries” (Lynch, 1991)—such as births and deaths of species and higher taxa and the shapes and diversity of radiations (Valentine, 1990). In discussions of evolutionary phenotypic transitions like those of part II, it means major phenotypic change (Lincoln et al., 1982). Rensch (1960) defined macroevolution as “evolution above the species level.” Microevolution, by contrast, is evolution below the species level, such as adaptive phenotypic and genetic change within populations, and geographic variation within a species. According to Simpson (1953a), the terms “macroevolution” and “microevolution” were invented by Goldschmidt (1940 [1982]), who also claimed that they involve different kinds of evolution. This problematic idea dates back to antiquity (see Rensch, 1960, for a concise review). The macroevolution problem, with emphasis on phylogenesis, was among other things (see Vuilleumier, 1984) behind the skepticism regarding Darwinism promoted by the enormously respected and influential French zoologist P.-P. Grassé. Grassé was convinced that the neo-Darwinian approach, with its emphasis on microevolution, cannot account for the primary features of evolution, namely, the large-scale diversification of life into major phylogenetic branches separated by unbridged gaps (e.g., see Grassé, 1973). This challenge echoes in the writings of many other critics of neo-Darwinism (e.g., Ho and Saunders, 1984; Gould and Eldredge, 1977; Gould, 1994; see also below), especially those who wish to contrast multilevel selection (including species selection) with microevolutionary theories (see Gould, 1999). The two macroevolution concepts, like the homology concepts discussed in chapter 25, are used interchangeably without sufficient attention to potential confusions. The result is needless controversy. The phylogenetic definition, for example, implies that macroevolution cannot, by definition, occur within species, for it refers exclusively to patterns above the species level. The phenotypic, major-change definition, on the other hand, can include processes within species.