No, Humans Are Not Chimp-Pig Hybrids

Back in July of this year, Eugene McCarthy proposed that humans are the result of hybridization between chimps and pigs. This didn't get much attention at the time, but today's Daily Mail discussed it, so there might be an upswing of attention.



Who is the claimant
Eugene McCarthy acquired his BS (in Mathematics), MS (in Genetics) and PhD (in Genetics) at the University of Georgia; the last of these degrees he acquired in 2003. According to his Google+, he is a geneticist, evolutionary theorist, author, and web entrepreneur, and his employment for the last 5 years has been his website, macroevolution.net.

To quote from macroevolution.net:
During my years at the genetics department, I became increasingly dissatisfied with the standard explanation of evolution. The more I read about fossils, the more convinced I became that Darwin's account of the evolutionary process was fundamentally flawed. Moreover, in my study of hybrids I became aware that an alternative way of thinking about evolution, what I now call "stabilization theory," could do a better job of explaining the available data.

So in his own words, Dr. McCarthy thinks evolutionary science is wrong somehow but thinks he knows better. Dr. McCarthy does have a book about bird hybrids published by Oxford University Press, which appears to be his most recent published scientific work; his attempts to publish a similar book about mammals and about his new theory of animal origins have not worked out, possibly because of his claims...

What is the claim
Various apes have mated, produced viable offspring, and continued mating with various species of pigs, and this mating has produced some of the modern and extinct species of apes. In particular, humans are the result of mating between, to quote from the above-linked article from phys.org, "a male boar or pig (Sus scrofa) with a female chimp (Pan troglodytes)".

Why this claim is probably, almost definitely, wrong
PZ Myers at Pharyngula discussed some of the reasons why this hypothesis can not be true, but I will just place the most obvious ones here:

1) The only evidence that Dr. McCarthy offers in support of this claim are morphological and behavioural "similarities" between pigs and humans. Morphology is useful for determining evolutionary relationships, but it can be misleading if where that morphology came from (the ontogeny of the morphology; what did the anatomy look like in embryos/fetuses/neonates/juveniles) is not investigated. That kangaroos and humans both walk on their hindlimbs only is a meaningless observation unless there is evidence that we both acquired that trait in the same way.

2) Dr. McCarthy makes this extreme evolutionary hypothesis without discussing the genome very much, which is odd, for a geneticist. But he gives no genomic evidence, whatsoever, that human evolution had porcine input. In fact he states, on the linked page, that there is no reason to suppose that the genes derived from pigs in modern humans would be sequentially similar to those of pigs, because a given type of gene is very rarely present in only a single type of organism. While the second part of his sentence is true, there should be genetic similarities between pig and human genomes if any of the human genome is derived from pig. He offers no such evidence, possibly because every published genomic study of pigs, human, and non-human apes suggests that the former are only distantly related to the latter two.

3) Pigs and apes are both placental mammals, but not very related to one another. So their last common ancestor may have been sometime in the late Cretaceous, 70ish million years ago. The claim that the gametes of a pig and a chimp would be compatible in any sort of way requires evidence that other such large crosses are possible. Dr. McCarthy has no such evidence, although he thinks he does, which results in such bizarre claims as claiming that platypuses and echidnas (the most primitive living mammals) are the results of crosses between birds and mammals, which last shared a common ancestor at least 300 million years ago. Such an idea has been refuted for over a century.

Does this claim deserve attention?
This claim was first posted online in July and it didn't get much press because it's ridiculous. So I'm really confused as to why the Daily Mail is giving it any press now, almost five months after it was first thrown online. Well, I'm not totally confused, but I'll get back to that.

No, it doesn't deserve attention. The author is a modern day Charles Fort in the sense that he is really good at tracking down small pieces of data in order to support a seemingly nonsensical conclusion. But in the scientific world, hypotheses deserve to be tested.

Four years ago a paper was published in PNAS that hypothesized that some members of insects are the result of a hybridization event between adult insects and velvet worms which produced caterpillars which eventually mutated and became other forms of insect larvae. That such a paper was published in the fourth most powerful journal in life/earth sciences was very confusing. Even a subsequent commentary letter published in PNAS asked WTF the journal was thinking. To quote from that letter,

This paper has fallen through the cracks of the review process of one of the most prestigious scientific journals, and this has not passed unnoticed. Online debates have erupted between those appalled that such article has appeared in a scientific forum and those who feel that scientific debate requires that all ideas, no matter how ill- formed, be discussed. But we should ask whether an individual can propose any theory, no matter how unsupported that idea may be, and demand that others do the work to test it scientifically.

Dr. McCarthy's hypothesis demands that others do the work to test it scientifically, while ignoring multiple lines of scientific evidence that it is wrong, and even making false claims about the hybridization abilities of mammals to the extreme of claiming that mammals and birds used to (or still can?) be able to produce viable offspring.

Why did the Daily Mail publish this?
The Daily Mail is known for its less-than-stellar record in discussing scientific research. Even if no malice was meant, promoting this research as if it is something that an actual scientist thinks (note that the Daily Mail refers to Dr. McCarthy as a leading geneticist, even though some of his most recent genetics work was published in 2004) results in the public thinking ill of scientists. When the Daily Mail introduces Dr. McCarthy as "Eugene McCarthy, of the University of Georgia", (which is a false statement; Dr. McCarthy, as far as I can tell, is not employed by the University of Georgia, and hasn't been for several years), that allows the audience to think ill of the University of Georgia in particular but academia in general.

While I don't think that the author of the piece intended to make light of evolution, evolutionary theory, or scientists in general, I am well aware of the hostility that the Daily Mail has for "controversial" scientific subjects.

Publicizing ridiculous independent, unpublished scientific hypotheses at the same level as academically-scrutinized published scientific papers confuses the lay audience into thinking that all scientific research is similarly incompetent. In the Information Age, wherein everyone has the same ability to throw something online, not discriminating between "this is something some loonie put online" and "this is a well-researched study reviewed by independent authorities" leads to all kinds of pseudoscientific nonsense, some of which just plain kills people.