CHIMPANZEES should take their rightful place alongside humans within the genus Homo. The biologists behind the resurrection of this controversial idea, say that the latest advances in genetics reveal greater similarities than differences between chimps and people. If they get their way, the reclassification would inflame the moral and philosophical debate over the conservation of chimp populations decimated by the bush-meat trade and Ebola, as well as their use in animal experiments.
Traditionally, chimps have been classified with the other great apes, gorillas and orang-utans, in the family Pongidae, which is separate from the human family Hominidae. But recent genetic studies have shown that chimps are closer to humans than either are to gorillas, forcing an overhaul of that classification scheme. And now Morris Goodman of Wayne State University in Detroit and his colleagues have found that humans and chimps are genetically more similar than we thought. Both living chimp species, the chimpanzee (Pan troglodytes) and the bonobo or pygmy chimpanzee (Pan paniscus), share 99.4 per cent of certain functional DNA sequences with humans.
With that close a relationship, the two chimp species belong in Homo, Goodman says, along with humans and our hominid ancestors including Australopithecus and Ardipithecus.
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The idea is not new 鈥� twelve years ago physiologist and ecologist Jared Diamond dubbed humans 鈥渢he third chimpanzee鈥� (快猫短视频, 13 July 1991, p 41). But genetic comparisons between apes and humans have so far yielded varying results depending on how the genotypes are compared.
Goodman compared published sequences of 97 genes from six species, including humans, chimps, gorillas, orang-utans and Old World monkeys. His team examined non-synonymous DNA: over time natural selection changes the bases in such sequences, and the resulting amino acids they code for. They found that 99.4 per cent of these bases are identical within the same genes for humans and chimps. Less functional sequences, where bases can change without affecting amino acids, were 98.4 per cent similar (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1232172100).
These new figures are much higher than the 95 per cent reported last year by Roy Britten of the California Institute of Technology (快猫短视频, 28 September, p 20). But Goodman says most of the DNA sequences Britten studied do not code for proteins, and are therefore not important for genetic function.
The small difference between genotypes reflects the recent split between chimps and humans, says Goodman. His genetic data suggests that occurred 5 to 6 million years ago (see Diagram). Goodman says the time when two animals split apart should dictate whether they belong within the same genus. Species of kangaroo that are placed in the same genus split between 8 and 14 million years ago, he points out. But Sandy Harcourt, an anthropologist at the University of California at Davis, believes that chimps and humans actually split between 6 and 10 million years ago. That is 鈥渁n awful long time to be in the same genus鈥�, he says.
