11 - Patterns of variation and speciation in Quaternary rodents

Summary

The tenth-anniversary issue of Paleobiology (Vol. 11,1985) summarized much of what paleontology has contributed to evolutionary theory and also raised many provocative issues. Gould (1985), for example, proposed that manifestly different evolutionary processes operate at three temporal levels, which he called “tiers.” He defined these tiers as (1) events measured in ecological moments, (2) evolutionary trends over millions of years, and (3) periodic mass extinctions. The theory of punctuated equilibrium was also a dominant theme of Gould's paper, and it remains an important and influential model today, despite Levinton's (1988) articulate criticisms. According to Gould and other proponents of punctuated equilibrium (e.g., Stanley, 1975,1979,1985; Vrba, 1983), microevolution and macroevolution are not necessarily reflections of a single underlying process variously expressed as a function of temporal scale; rather, the two have fundamentally different causative agents. Natural selection, for example, may have a higher-order analogue at the species level (Stanley, 1975; Vrba, 1983). In contrast, Gingerich (1983, 1985) and Levinton (1988) generally support the position that natural selection among individuals and adaptation are the primary driving forces at all hierarchical and temporal levels – the standard Darwinian paradigm. If the process of punctuated equilibrium dominates in the history of life, and if most significant morphological change is concentrated during speciation events, then phyletic change should be, as Stanley (1979) suggests, only the fine-tuning of an organism to its environment.