That’s one idea put forward by Eugene M. McCarthy, a self-professed expert on hybridization who has a PhD in genetics from the University of Georgia. To summarize, he has written a lengthy stream of blog posts arguing that our species is the product of hybridization between a pig and a chimp (or perhaps a bonobo).

First things first: this idea is as fringe as it gets and not accepted by the overwhelming majority of geneticists, paleoanthropologists, and so on. As Carl Sagan said, extraordinary claims require extraordinary evidence, and this argument lacks the scientific rigor and genetic proof needed to take it seriously. 

It’s so outlandish that you might suspect it’s a deliberate bombshell – satire in disguise or a clever critique. That said, McCarthy insists his hypothesis is not a hoax, a parody, or an act of grade-A trolling.

Explaining his hypothesis in a nutshell, McCarthy writes on his website MacroEvolution: “I suggest that the facts we have from observation better fit the supposition that a chimpanzee- or bonobo-like animal anciently crossed with a pig to produce an offspring that then mated back (‘backcrossed’) to a chimpanzee (than the supposition that our lineage has gradually diverged from the apes).”

To set the stage for his proposal, McCarthy attempts to address some misunderstandings about hybrids. Firstly, it isn’t true that all hybrids are sterile or unable to produce fertile offspring. Secondly, the natural world is full of examples of hybridization, which is widely recognized as a potent force in the evolution of different, new species.

Humans, at surface level, might look a bit like elongated chimps that have lost most of their body hair and gained some pig-like flab. Apparently, the flesh of humans is said to taste a lot like pork too, but let’s not get into that right now…

McCarthy runs through several features that make Homo sapiens stand apart from their great ape cousins, but are present in pigs, such as cartilaginous noses, thick eyelashes, multi-pyramidal kidneys, “naked” skin, vocal cord structure, circular folds in the small intestine, the absence of a penis bone (baculum), and more. 

So, what about the genetics? The crossover with chimpanzees and bonobos is very clear; Homo sapiens share close to 99 percent of their genome with these non-human primates. With pigs, the link is less clear, although McCarthy claims that “it can be very difficult to identify later-generation backcross hybrids derived from several repeated generations of backcrossing.” In other words, he argues that evidence of inter-species breeding can be lost when looking at genetic sequencing data from countless generations ago.

Many, many scientists have bitten back against the pig-chimp hybrid hypothesis, drenching it in scorn and relentless skepticism.

In a (since deleted) blog post, palaeontologist Donald Prothero wrote: “Anyone trained in genetics or evolution will immediately do a double-take reading this, because it [is] so far off the edge of crazy that it cries out to be examined further. So you click on the link, and what do you find? Is there a ton of genetic data, peer-reviewed and published in a respectable journal, that would allow us to take the claim seriously? No, not even close.”

“He’s just another crackpot trying to do his own version of evolution without [the] benefit of learning from the rest of science, or listening to more rational scientists (who should have trained him better years ago),” Prothero adds.

McCarthy has, in turn, written rebuttals to Prothero and his other critics. However, his bold hypothesis remains untested and unsubstantiated by hard data. While the pig-chimp hybrid idea makes for an entertaining thought experiment, it stands on shaky scientific ground and, as Prothero put it, remains firmly in the realm of “hogwash”.