For populations numbering in the thousands, he says, "there is an advantage to keeping distinct populations separate, because in mixing them you could lose some critical genetic diversity." However, "the opposite is true once you get below a threshold number and don't have a full representation of genetic types." Muir worries that maintaining captive Sumatrans and Borneans separately risks falling below that threshold.
Groves not only agrees that Borneans and Sumatrans are distinct subspecies and should not be interbred, he also says that "eventually, we'll be proposing that these [Bornean populations] be formally recognized as subspecies." The Bornean skull differences he has observed are not visible in living animals.
He also argues that zoos and other game managers should attempt to establish that Borneans paired for mating trace back to the same geographically distinct parent population.
"So our only options now are to just breed them as Borneans or to not breed any Borneans -- which would send the [captive] population into a crash from which it probably would not recover."
The American Association of Zoological Parks and Aquariums (AZA) adopted a policy 10 years ago to stop interbreeding Sumatran and Bornean orangutans -- and to prevent any of AZA's hybrid offspring (now numbering 51) from reproducing.
Seuanez of the Federal University of Rio de Janeiro and his coworkers published data demonstrating a clear difference between Sumatran and Bornean orangutans -- an inversion, or consistent rearrangement of genetic material, in a region of chromosome 2.
The festival is anchored on folk history, specifically the Barter of Panay which involves the story of 10 Bornean
datus who fled to and established a new home in Panay Island after fleeing a dictatorial regime in Borneo sometime in the 13th century.