for National Geographic News
The authors base their conclusion on a close physical resemblance between orangutans and humans, which they say has been overshadowed by genetic evidence linking us to chimps.
What's more, the study authors argue, the genetic evidence itself is flawed. (Get a genetics overview.)
John Grehan, of the Buffalo Museum of Science in New York State, and Jeffrey Schwartz, of the University of Pittsburgh in Pennsylvania, say that the DNA evidence cited by many scientists only looks at a small percentage of the human and chimp genomes.
What's more, the genetic similarities likely include many ancient DNA traits that are shared across a much broader group of animals.
By contrast, humans share at least 28 unique physical characteristics with orangutans but only 2 with chimps and 7 with gorillas, the authors say.
The finding, which has the potential to spark a radical rethink of human origins, is being met with caution.
"There are many paleontologists and molecular biologists who are heaping scorn on this paper," noted Peter Andrews of the Natural History Museum in London.
Even though he still backs the human-chimp relationship, Andrews had recommended that the study be published, and it now appears in the June issue of the Journal of Biogeography.
"It is controversial," he said, "but I think it is a subject that needed to be aired."
With the sequencing of the chimpanzee genome in 2005, scientists found direct proof that humans and chimps are 96 percent the same genetically.
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