Estimation of branching dates among primates by molecular clocks of nuclear DNA which slowed down in Hominoidea

Estimated divergence dates from DNA sequence data suggest that human separated from the African apes about 4 ∼ 7 My ago.

Abstract

As there is evidence that the nucleotide substitution rate of globin gene region in nuclear DNA has decreased in Hominoidea compared to Cercopithecoidea, we have developed a statistical method for estimating divergence dates from DNA sequence data taking into account of the possible variation of the rate among lineages, and applied it to the data of ψη-globin gene and of intergenic spacer between ψη and δ-globin genes from primates. The ψη-globin gene data suggest a further decrease of the rate in the human line relative to the great ape lines, while the intergenic spacer data suggests the opposite tendency, although weakly. The molecular clock with variable rate was calibrated by setting the data of divergence between platyrrhines and catarrhines at 30 My ago based on a recent revision of the date of the earliest platyrrhine Branisella (MacFadden et al., 1985). The ψη clock gave dates of 21·54 ± 1·90, 12·34 ± 1·76, 6·75 ± 1·13, and 6·54 ± 1·12 My ago (where the number after ± is the standard error) for the separation of rhesus monkey, orang-utan, gorilla and chimpanzee, respectively from the line leading to human. The intergenic spacer clock gave dates of 21·08 ± 1·89, 11·16 ± 1·89, 4·73 ± 1·19, and 4·38 ± 1·26 My ago (±: S.E.) for the separation of rhesus monkey, orang-utan, chimpanzee, and gorilla from human. These estimates suggest that human separated from the African apes about 4 ∼ 7 My ago.