LONDON: Humans are actually hybrids, who emerged as an offspring of a male pig and a female chimpanzee, according to one of the world's leading geneticist.Turning the theory of human ancestry on its head, Dr Eugene McCarthy — one of the world's leading authorities on hybridization in animals from the University of Georgia has suggested that humans didn't evolve from just apes but was a backcross hybrid of a chimpanzee and pigs.His hypothesis is based on the fact that though humans have many features in common with chimps, there are a lot more that don't correspond to any other primates. He then suggests that there is only one animal in the animal kingdom that has all of the traits which distinguish humans from our primate cousins."What is this other animal that has all these traits? The answer is Sus scrofa - the ordinary pig" he says.He explains: "Genetically, we're close to chimpanzees, and yet we have many physical traits that distinguish us from chimpanzees. One fact, however, suggests the need for an open mind: as it turns out, many features that distinguish humans from chimpanzees also distinguish them from all other primates. Features found in human beings, but not in other primates, cannot be accounted for by hybridization of a primate with some other primate. If hybridization 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."Dr McCarthy suggests that Charles Darwin told only half the story of human evolution "We believe that humans are related to chimpanzees because humans share so many traits with chimpanzees. Is it not rational then also, if pigs have all the traits that distinguish humans from other primates, to suppose that humans are also related to pigs? Let us take it as our hypothesis, then, that humans are the product of ancient hybridization between pig and chimpanzee," he said.According to Dr McCarthy, if we compare humans with non-mammals or invertebrates like the crocodile, bullfrog, octopus, dragonfly and starfish, pigs and chimpanzees suddenly seem quite similar to humans.Pigs and chimpanzees differ in chromosome counts. The opinion is often expressed that when two animals differ in this way, they cannot produce fertile hybrids. This rule is, however, only a generalization. While such differences do tend to have an adverse effect on the fertility of hybrid offspring, it is also true that many different types of crosses in which the parents differ in chromosome counts produce hybrids that capable themselves of producing offspring.There is substantial evidence supporting the idea that very distantly related mammals can mate and produce a hybrid.Another suggestive fact, Dr McCarthy says 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. "Serious efforts are now underway to transplant kidneys and other organs from pigs into human beings. 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 said."It might seem unlikely that a pig and a chimpanzee would choose to mate, but their behaviour patterns and reproductive anatomy does, in fact, make them compatible. It is, of course, a well-established fact that animals sometimes attempt to mate with individuals that are unlike themselves, even in a natural setting, and that many of these crosses successfully produce hybrid offspring," he adds. Dr Eugene McCarthy says that the fact that even modern-day humans are relatively infertile may be significant in this connection."If a hybrid population does not die out altogether, it will tend to improve in fertility with each passing generation under the pressure of natural selection. Fossils indicate that we have had at least 200,000 years to recover our fertility since the time that the first modern humans (Homo sapiens) appeared. The earliest creatures generally recognized as human ancestors (Ardipithecus, Orrorin) date to about six million years ago. So our fertility has had a very long time to improve. If we have been recovering for thousands of generations and still show obvious symptoms of sterility, then our earliest human ancestors, if they were hybrids, must have suffered from an infertility that was quite severe. This line of reasoning, too, suggests that the chimpanzee might have produced Homo sapiens by crossing with a genetically incompatible mate, possibly even one outside the primate order," he said.