MANS PLACE IN HOMINOIDEA REVEALED BY MITOCHONDRIAL-DNA GENEALOGY

Molecular biology has resurrected C. Darwin and T. H. Huxley's question about the origin of humans, but the precise branching pattern and dating remain controversial. To settle this issue, a large amount of sequence information is required. We determined mitochondrial (mt) DNA sequences for five hominoids; pygmy and common chimpanzees, gorilla, orangutan, and siamang. The common region compared with the known human sequence is 4759 bp long, encompassing genes for 11 transfer RNAs and 6 proteins. Because of the high substitution rates in mammalian mtDNA and an unprecedentedly large region compared, the sequence differences clearly indicate that the closest relatives to human are chimpanzees rather than gorilla. For dating the divergences of human, chimpanzee, and gorilla, we used only unsaturated parts of sequence differences in which the mtDNA genealogy is not obscured by multiple substitutions. The result suggests that gorilla branched off 7.7 +/- 0. 7 million years (Myr) ago and human 4.7 +/- 0.5 Myr ago; the time difference between these divergences being as long as 3 Myr.