Closer to man than ape
ˇ DNA study supports call to reclassify chimpanzeesˇ 'Historic differences' may not be so great, tests find
Ian Sample, science correspondentTuesday January 24, 2006The Guardian
They already use basic tools, have rudimentary language and star in TV commercials, but now scientists have proof that chimpanzees are more closely related to humans than other great apes.
Genetic tests comparing DNA from humans, chimps, gorillas and orang-utans reveal striking similarities in the way chimps and humans evolve that set them apart from the others.
The finding adds weight to a controversial proposal to scrap the long-used chimp genus "Pan" and reclassify the animals as members of the human family. The move would give chimps a new place in creation's pecking order alongside humans, the only survivor of the genus Homo.
The biologist Soojin Yi's team at Georgia Institute of Technology in Atlanta compared 63m base pairs of DNA from different species, where each base is a letter in the animal's genetic code. They then analysed the DNA to look at what evolutionary biologists call the molecular clock, the rate at which an animal's genetic code evolves. The speed of the clock shows how the span of a generation has changed over the millennia.
The tests showed that even though humans and chimps split from a common ancestor between 5m and 7m years ago, the rate at which their genetic codes were evolving was extremely similar, differing by only 3%, and much slower than gorillas and orang-utans.
A slow molecular clock suggests that the time between generations is long, something that has historically set humans apart from the great apes. Team member Navin Elango said: "We found that the chimpanzee's generation time is a lot closer to that of humans than it is to other apes."
According to the scientists, whose study appears today in the US journal Proceedings of the National Academy of Sciences, the finding suggests some human traits only emerged 1m years ago, a fleeting moment on evolutionary scales.
"This study provides further support for the hypothesis that humans and chimpanzees should be in one genus, rather than in two different genuses, because we not only share extremely similar genomes, we share similar generation time," said Dr Yi.
Doubts over the chimp's position in the evolutionary tree have been around from the start. In 1775, when scientists first got around to naming the chimpanzee, they noted the similarity with people and placed them next to humans under the genus Homo. But by 1816 chimps had been pushed out into their own genus, Pan, which has survived to this day.
In 1991, the Pulitzer prize-winning ecologist Jared Diamond called humans "the third chimpanzee", setting us alongside the common chimp (Pan troglodytes) and its less aggressive but astoundingly promiscuous cousin, the bonobo (Pan paniscus). By 1999 confusion over the biological status of chimpanzees prompted scientists in New Zealand to join forces with lawyers to petition the country's government to pass a bill conferring "rights" on chimpanzees and other primates. The move drew derision. Roger Scruton, the moral philosopher, asked: "Do we really think that the jails of New Zealand should henceforth be filled with malicious chimpanzees? If not, by what right are they to be exempted from punishment?" New Zealand granted great apes legal protection from animal experimentation. British Home Office guidelines also forbid experiments on chimps, gorillas and orang-utans.
In 2003, researchers at Wayne State University in Detroit again ignited the debate when they found that 99.4% of the most critical DNA sites are identical in human and chimp genes, prompting the lead researcher, Morris Goodman, to declare that chimps and humans should be brought together under the same umbrella genus, Homo.
"There have been discussions about whether chimpanzees should be afforded more protection and this might make things a bit clearer in peoples' minds about whether they should have rights of some kind. In terms of life on Earth, chimps and humans are really not that different to each other," said Andrew Rambaut, an evolutionary biologist at Oxford University. Practically, he adds, reclassification could raise the chimp's profile and potentially improve their conservation.
"It seems a bit human-centric to want to put chimps into the 'Homo' genus and not reclassify humans as 'Pan'. But these things are arbitrary, once you've divided it into species. It would become a more political decision than anything else," he said.