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Chimps May Belong in Human Genus

June 10 2003

A new analysis of functionally important genetic differences suggests that chimpanzees and humans diverged from a common ancestor to a similar extent and that both species should be grouped in the genus Homo. Chimpanzees, gorillas, and other apes have traditionally been separated from humans in taxonomic schemes, with humans considered the only living members of the family Hominidae and the genus Homo. In “Implications of natural selection in shaping 99.4% nonsynonymous DNA identity between humans and chimpanzees: Enlarging genus Homo,” Morris Goodman and colleagues tested the validity of these taxonomies by comparing 97 genes from six different species: humans, chimpanzees, gorillas, orangutans, Old World monkeys, and mice. Based on genetic mutations that affect protein production and are thus functionally important, the scientists constructed an evolutionary tree that measured the degree of relatedness among the six species. According to this analysis, chimpanzees and humans occupy sister branches on a family tree, with 99.4% genetic similarity. Next on the tree are gorillas, then orangutans, followed by Old World monkeys. None of the primates were closely related to mice, which were used as a control. By tracking the mutation rates in each species, the researchers estimate that humans and chimpanzees diverged from a common ancestor roughly 5 to 6 million years ago. This common ancestor, in turn, diverged from gorillas about 6 to 7 million years ago. These results support two previously offered taxonomic proposals: that all extant apes should occupy the family Hominidae, and that both humans and chimpanzees should occupy the genus Homo.

“Implications of natural selection in shaping 99.4% nonsynonymous DNA identity between humans and chimpanzees: Enlarging genus Homo” by Derek E. Wildman, Monica Uddin, Guozhen Liu, Lawrence I. Grossman, and Morris Goodman, PNAS 2003 100: 7181-7188; published online before print as 10.1073/pnas.1232172100

Abstract © 2003 PNAS

Derek E. Wildman, Center for Molecular Medicine & Genetics, Wayne St. University School of Medicine