That said, this is way, way too far fetched. Proposing that a primate and a primitive ungulate can produce an hybrid is already a big stretch, let alone producing a fertile one. Then, he supports his claim by refusing the genetics, and hand picks morphology aspects from the suinae that confirm his theory.
What did it for me was the "naked skin" evidence though. It's the human-selected, domestic pig that is hairless.
A primate/primitive ungulate don't need to produce a hybrid or fertile offspring since obviously aliens mixed chimpanzee and pig DNA to create us, a race of slaves to mine gold for them.
They also removed our ability to synthesize vitamin C in the process as a method of control.
Is there some evidence that the hairless trait was the result of human selection and no hairless varieties existed before human selection?
That is still a pretty weak argument considering from all suinae, the domestic pig is the only hairless, and for his hypothesis to work, hairlessness would have to be a dominant trait (otherwise, logic says we should be hairy like a chimp).
I'm no geneticist or anything like that, but there are some pretty (big) holes that he doesn't address and attributes to ignorance. You can't make an hypothesis plausible by claiming about what you do NOT known - you have to show positive correlation, not absence of negative correlation.
All useful hypothesis are, by definition, extra-ordinary.
Not in the sense of that applies to that saying. In this context "extraordinary claim" means "claim with a very low prior probability". The saying can be expressed more precisely as "in order to upgrade to the level of expectation a hypothesis with a very low prior probability, it is necessary to make an observation of very low probability generally, but high probability given that the hypothesis is true." In other words, it's essentially just Bayes' theorem.
And by no means are very-low-prior hypotheses inherently more useful. Certainly they have more impact than higher-prior hypotheses if they are validated, but in general, a very low prior means that a hypothesis is not worth wasting time considering.
In some cases, a hypothesis can be so extraordinary that it becomes practically impossible to verify by experiment. In this case, for example, the hypothesis is so unlikely that it is quite difficult to imagine an experiment (or set of experiments) whose outcome was so unlikely that it would actually make us expect that humans were descended from ape-pigs.
Reading a bit more, it seems like he's got expertise in a corner of science that could be relevant to what the article calls 'morphological change':
"As the increasing apparent, magnificant, speed with which morphological change can occur continues to present itself for us to comprehend, the standard theory of random mutation followed by slow environmental selection, seems to stall. In my own opinion, female choice ... , but other mechanisms of mutation ... , now need to be considered anew. The role of hybridization in driving morphological change, as McCarthy has observed time and time again, particularly in his studies of avian species ... , may be the most powerful mechanism of all."
Okay, so if the "speed of change" problem is a pretty wide-open question without a lot of firm answers, and if this guy has staked out a claim in the problem space ... my reaction is basically "good on ya'!"
Go play god with interspecies breeding and come back in 5 years with an update. :)
Minor nitpick, but while Sagan popularized the saying, it probably originates with Laplace's "The weight of evidence for an extraordinary claim must be proportioned to its strangeness" (which is itself a rephrasing).
This makes sense in historical context; the quote comes from 1814, two years after Laplace published the most well-known formulation of Bayes' theorem, which is exactly what the saying embodies.
1) A hybridization event indeed occurred in the relatively recent genetic history of homo sapiens (rather than the unusual anatomic features being produced some other way).
2) The hybridization was with a close relative of pigs (rather than another family that has some similar characteristics, or multiple hybridizations that together gave us the unusual characteristics).
3) The hybridization marks the point at which hominids split from the other primates (rather than occurring later in one branch of the hominid family tree).
4) That the genes introduced by hybridization gives hominids their unique characteristics (rather than being inconsequential).
In return, the theory presents evidence (anatomic oddities and low fertility) that I would characterize as "interesting" and perhaps "worthy of further study", but certainly not extraordinary. For this to be plausible, there needs to be a second avenue of evidence, one not based on anatomic similarities...
That second avenue could be genetic, but they specifically dismiss it, presupposing a mechanism, backcrossing, that leaves little genetic evidence that it occurred. Now, I'm no geneticist, but that sounds a bit fishy to me.