The Northwestern researchers compared mitochondrial DNA—a kind of DNA inherited only from the mother—and found that the kouprey's genetic makeup is so similar to that of the banteng that the most probable conclusion is that the kouprey is not a natural species at all.
Instead it is likely a feral form of a domestic animal, the scientists say, probably a hybrid of the mainland banteng and the zebu, strains of both of which are common among domestic oxen in Southeast Asia.
"We do know the mitochondrial DNA for the kouprey," Galbreath said. "If the kouprey was a domestic hybrid, our notion was to see if Cambodian banteng were similar to kouprey. And sure enough, as predicted, they were.
"[We] made a genetic prediction that most people wouldn't have believed correct, but we found that it was correct," he added.
The authors note that Cambodian farmers in the recent past reportedly used a kind of semi-feral ox to work in rice fields. This animal, the authors suggest, may have been the kouprey—living wild but still partially dependent on human contact.
"Considerable Debate"
The conclusion made by Galbreath and his colleagues is controversial, and some experts regard it as premature.
"There are several other scenarios that would explain their finding equally well," said Hans Lestra, associate professor of genetics at Utrecht University in the Netherlands.
"If the kouprey is of mixed-species origin, hybridization with domestic zebus is just one of the possibilities. Maybe, maybe not."
Lestra also argues that the team's study—which appears in the Journal of Zoology—doesn't live up to its title: "Genetically Solving a Zoological Mystery."
"No genetic mystery has been solved," Lestra said. "For this, additional research would be required, such as a comparison of paternally transmitted Y-chromosomal sequences of kouprey with those of banteng and zebu. However, Galbreath [and team] never analyzed any kouprey samples."
"By 'solving the mystery,' we mean making a step toward that," Galbreath responded.
"We're not claiming that an absolute conclusion can be come to at this point, but the most probable explanation is that this is an escaped domestic species."
Alexandre Hassanin of France's National Museum of Natural History says that the case remains unsettled.
In a paper still under review, he writes that "we need to … analyze banteng from Laos, Myanmar, Thailand, and Vietnam to give a definitive conclusion on the taxonomic status of banteng and kouprey."
Galbreath agrees that more data is needed.
"This is going to set off a considerable amount of debate," he said, "and that's part of our purpose. This is certainly going to stimulate people to obtain other kinds of genetic information from other wild cattle, particularly banteng."
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