DNA/DNA HYBRIDIZATION STUDIES OF MUROID RODENTS: SYMMETRY AND RATES OF MOLECULAR EVOLUTION.

Abstract

Data from several sources suggest that molecular and organismal rates of evolution often differ (Sarich and Wilson, 1967a, 1967b; Wilson et al., 1974a, 1974b, 1977; Prager and Wilson, 1975; Bruce and Ayala, 1979; Ferris et al., 1981). Protein molecules, for example, are useful systematic tools because they seem to evolve in a stochastically regular manner (Fitch, 1976). In contrast, others note that rates of morphological evolution seldom exhibit such time-dependence (Eldredge and Gould, 1972). The source of comparative data thus influences perceptions of species relatedness, taxonomic status, and divergence time (c.f. Byrd, 1981). For example, on the basis of electrophoretic and immunological analyses, human and chimpanzee might be considered as sibling species that diverged 4-6 million years ago (MYA) (Sarich and Wilson, 1967a, 1967b; Wilson and Sarich, 1969; King and Wilson, 1975; Sarich and Cronin, 1976; Wilson et al., 1977). However, on the basis of morphological characters, human and chimpanzee are placed in different families (Hominidae and Pongidae), and their divergence from a common ancestor is placed earlier (Pilbeam, 1970; Simons, 1976; see also Bruce and Ayala, 1979). To reconcile the apparent disagreement between morphologicallyand biochemically-based primate classifications and divergence estimates, Uzzell and Pilbeam (1971) and Goodman et al. (1971) proposed that biochemical similarities might be a result of an evolutionary slowdown within the hominoid lineage. Sarich and Wilson (1973) evaluated this hypoth-