A radical new idea on how humans may have come to exist has been proposed by an American geneticist; he believes that humans are hybrids of chimpanzees and pigs, and no, he isn’t joking.
The idea first hit the blogosphere in early July and has received a resurgence of Twitter attention in recent weeks. Dr Eugene McCarthy, formerly of the Genetics Department at the University of Georgia, published the hypothesis in a lengthy discourse on his website macroevolution.net. The story received further attention when the science news website phys.org published two articles in support of the idea.
Dr McCarthy holds a PhD in genetics and is an acknowledged expert on hybrids. His book Handbook of Avian Hybrids of the World was published by Oxford University Press in 2006 to favourable reviews. He has since been amassing evidence for an alternative theory of evolution on his website, centring on the idea that species do not undergo great changes but are instead stable from their ontogeny to their extinction. New species, he says, most likely arise as a result of hybridisation. This differs drastically from the conventional view that species change gradually over time in response to their environment: natural selection, as proposed by Charles Darwin.
Hybrids are well-documented in nature, and contrary to popular belief are not usually sterile; the mule is an unusual example. Many mammalian crosses produce fertile hybrids, such as the liger (lion-tiger hybrid) or the zedonk (zebra-donkey hybrid). These animals have both produced offspring when back-crossed with one of their parental species, such as a liger with a lion. A reduction in fertility is however a common feature of hybrids, which is what led Dr McCarthy to his unusual hypothesis.
Humans, he claims, are less fertile than other animals with males producing many abnormal sperm. Between this evidence and his belief that new species arise from hybridisation he set out to find our “parents”. The first seemed obvious: the chimpanzee is our closest living relative and we share 98% of the same DNA. He suggests that the hybrid offspring would have then lived among and repeatedly back-crossed with chimpanzees (is our ancestor Tarzan?), which is why we cannot deduce the second parent from DNA alone. He then turned to a method used by biologists when trying to identify an unknown hybrid: he compiled a list of anatomical and behavioural differences between humans and chimpanzees and tried to match these to another animal.
The list of characteristics is very long, but the main points include: hairless skin, protruding nose, omnivory, terrestrial lifestyle and features of the skeleton and internal organs. All of these traits, he claims, point to pigs. The only traits that didn’t fit this pattern were upright posture and large brain, but Dr McCarthy believes certain anatomical characteristics in chimpanzees and pigs would produce these traits when combined in a hybrid. He hypothesises the hybrid would have been born from the union of a male boar and a female chimpanzee. Relish that mental image for a moment.
There is some merit in the idea. Medical professionals already use porcine heart valves and skin tissue in transplants because of their compatibility with the human body, and many people have noted our similarities with pigs over the course of history (Animal Farm, anyone?)
There are a considerable number of counter-arguments. The major one brought up by critics, that of the drastically different chromosome numbers between the two species (pigs have 38 chromosomes whilst chimpanzees have 48) was answered by Dr McCarthy himself when he pointed out that the difference in chromosome numbers between zebras and donkeys is considerably higher. The greatest problem then is that whilst hybrids have been seen amongst different species of horse or big cat, and even it is thought among different human species (most people possess 2% Neanderthal DNA!) no hybrids from anywhere in nature have ever been found in such distantly related species, not even in plants which hybridise much more readily than animals. The fossil record also does not support this claim, but Dr McCarthy believes all fossil hominids may be a result of separate hybridisation events with pigs. This seems very unlikely.
As an aside, because I care about you as readers, porcine genitalia is remarkably bizarre and would have been quite traumatic if introduced into a primate system.
This hypothesis has received mixed reviews, with some people openly mocking the idea and others proclaiming themselves converts. Rather beautifully, it has united evolutionists and creationists in a mutual state of offence. It is an interesting idea that challenges conventional dogma and will certainly change a few opinions on bacon butties.
I myself am not convinced. We don’t fully understand everything that makes us human yet but research is progressing all the time and many questions are finding answers, none of which involve chimpanzees and pigs doing the prehistoric nasty.
Photo: Wikimedia Commons