The bizarre theory has been proposed by Eugene McCarthy, of the University of Georgia. In an article on his website macro-evolution.net, McCarthy wrote that humans are the result of multiple generations of back-crossing to the chimpanzee.
McCarthy said that in the case of chimp - pig hybridisation, the "direction of the cross" would likely have been a male boar or pig (Sus scrofa) with a female chimp (Pan troglodytes), and the offspring would have been nurtured by a chimp mother among chimpanzees, 'phys.org' reported.
One can suppose that humans are back-cross hybrids because humans are highly similar to chimpanzees at the genetic level, closer than they are to any other animal, McCarthy said.
He explained that if humans were descended without any back-crossing we would be about halfway, genetically speaking, between chimpanzees and whatever organism was the other parent. But we're not, he said.
Genetically, we're close to chimpanzees, and yet we have many physical traits that distinguish us from chimpanzees. This exactly fits the back-cross hypothesis, McCarthy claimed.
To support his theory, he points out that while humans have many features in common with chimps, we also have a large number of distinguishing characteristics not found in any other primates.
Features found in human beings, but not in other primates, cannot be accounted for by hybridisation of a primate with some other primate, he said.
If hybridisation is to explain such features, the cross will have to be between a chimpanzee and a non-primate - an unusual, distant cross to create an unusual creature.
The other parent in this hypothetical cross that produced the first human would be an intelligent animal with a protrusive, cartilaginous nose, a thick layer of subcutaneous fat, short digits, and a naked skin, he suggests.
Sus scrofa, the ordinary pig, possesses these traits, McCarthy said.
Another fact that supports the idea is the frequent use of pigs in the surgical treatment of human beings.
Pig heart valves are used to replace those of human coronary patients. Pig skin is used in the treatment of human burn victims, said McCarthy.
Serious efforts are now underway to transplant kidneys and other organs from pigs into human beings, he said.
"Why are pigs suited for such purposes? Why not goats, dogs, or bears ? Animals that, in terms of taxonomic classification, are no more distantly related to human beings than pigs?" He asked.