But chimpanzees are an endangered species. They are costly to raise, and they grow slowly to adulthood. Chimpanzees may also harbor unknown viruses that do them no harm but that might cause devastating diseases in humans diseases that might be transmitted to other people. For example, researchers have strong evidence that HIV crossed into humans from chimps during the first half of this century. Most xenotransplantation researchers agree that chimpanzees are not suitable organ donors.
Researchers also agree that other higher nonhuman primates such as baboons are out, too.
Although organs from these animals are less likely than those of more distant species to set off hyperacute rejection, they, too, harbor microorganisms that might leap to humans easily and with dangerous consequences. And like chimpanzees, baboons are costly to raise and, in some cases, suffer from population decline. Strange as it may sound, the animal that is emerging as the most likely source of transplantable organs is the pig. Pigs organs are the right size. The animals are highly domesticated, they have large litters, and they grow quickly to maturity.