It's quite telling that in this era of abundant genetic data, this guy bases all of his arguments on anatomical similarities and says nothing about genetics. It's all but impossible that a link like what he's suggesting would have been overlooked if pigs had made any significant contribution to the human genome. (Just for example, we've got all sorts of estimates of species divergence dates among primates based on genetic data that should have given nonsensical results if there had been massive influxes of pig DNA in the middle of that history.)

That being said, diluted gene contribution is not the same thing as no gene contribution. To even begin accepting such a theory I would require direct genetic evidence showing considerable horizontal gene transfer between porcine and hominid lines.

I'm not going to say that's impossible, but it sounds like one heck of a stretch. Even just sitting here thinking about it, most genetic inheritance happens one full chromosome at a time. We clearly don't have any full pig chromosomes, so to make this theory work you'd have to have a whole lot of lucky recombination events (chromosomal crossover, etc.) that preserved only the precise genes involved in all these "distinctive pig traits" and got rid of the rest. So what's the selective effect that selects extraordinarily strongly for this random selection of pig-like anatomical traits but against all of the other pig genes that would have usually been linked to them?

In short, this is a very extraordinary claim, and it requires equally extraordinary evidence, especially given how remarkably consistent the known genetic evidence has proven to be.

> most genetic inheritance happens one full chromosome at a time.

is actually not true. Sperm and eggs have only one copy of each chromosome instead of two like most cells in the body. However, that one chromosome is a pretty good mixture of the versions received from each parent due to recombination events that occur randomly during maturation of those cell types. Linkage between nearby genes does exist, but it's not nearly so strong as you seem to imply. Even in a single generation inheritance of two genes on either end of the same chromosome is nearly uncorrelated.

What he is suggesting is that a single hybrid made it's way back into the hominid population. It had children with other hominids, and those children would have had half as much pig DNA. They had children with even less, and so on. After awhile there would be almost nothing left of the pig ancestor. The only genes that would survive such dilution would be ones that were significantly selected for.

I understand the idea of dilution, I just don't understand why he thinks that so many random things would survive it to become defining features of the human species. Remember, he's not just saying that 2% of living humans carry Genghis Khan's Y-chromosome or have red hair or something, he's saying that all of these traits became completely universal.

I'm not certain how much mixing there was between the new and the old world. However it did happen a lot and it's likely a large number of people do have some new and old world ancestors.

1000 years ago, people in villages and towns were regularly marrying their (2,3,4) cousins and rarely marrying people from 'different lands'.

Another way to look at it: for 1 person to become the ancestor of just several thousand people takes 'a few generations'. Getting to whole populations takes lots of generations.

https://news.ycombinator.com/item?id=7539143

The author posted some replies, one of which points to this article:

http://phenomena.nationalgeographic.com/2013/05/07/charlemag...

That puts it at about 3400 years (the article gets the number from some paper on the topic).

Not exactly 1,000 years, but more like 120-135,000 years for the male line [1], and 200,000 years for the female line [2].

[1] "Sequencing Y Chromosomes Resolves Discrepancy in Time to Common Ancestor of Males Versus Females " dx.doi.org/10.1126/science.1237619

[2] https://www.princeton.edu/~achaney/tmve/wiki100k/docs/Mitoch...

http://gcbias.org/2013/11/11/how-does-your-number-of-genetic...

After ~15 generations your genealogical ancestors aren't all that likely to have contributed much to your DNA.

If a generation is about 30 years then you will have close to 33 ancestors lines in your family tree over those 1000 years. That makes 2^33 ancestors or 10 billion, that's impressive (well there is probably a large overlap)

http://en.wikipedia.org/wiki/Toba_catastrophe_theory

So, based on that, we're descended from fewer people in the past than most people realize. Another way to say it is that most of our ancestors were cousins.

http://phys.org/news/2013-07-human-hybrids-closer-theory-evi...

While goats and sheep diverged 8 million years ago, humans/chimps and pigs diverged 80 million years ago. The last time a proto-chimp got with a proto-pig, the T-Rex hadn't evolved yet. While goats and sheep have a difference of 6 chromosomes, chimps and pigs have a difference of 10. McCarthy, despite being a geneticist, makes his absurd claim without even discussing the genetic difficulties.

What little similarity there is between humans and pigs is simply a case of convergent evolution.

Another argument was that the morphological distance, or genetic differences besides chromosome number, are just too great. Most of us are familiar with the platypus. A paper published in Nature a few years ago demonstrated that the platypus genome contains both bird and mammal chromosomes, and therefore that the vastly different bird and mammal sex chromosome systems have been successfully bridged by this creature. This example is not offered as any kind of proof. But it does suggest that sometime, long ago, a cross occurred that would have been even more distant than that between a chimpanzee and a pig – one between a otter-like mammal and a duck-like bird. And if such was the case, the hybrids from the cross must have been able to produce offspring (otherwise they would have died out, and the platypus would not exist today).

http://phys.org/news/2013-07-human-hybrids-closer-theory-evi...

The platypus is not a bird/reptile hybrid. That is a wild misinterpretation of a genome study which happened a few years back.

http://scienceblogs.com/pharyngula/2008/05/10/the-platypus-g...

Most likely it's just someone stepping outside their wheelhouse. I mean, I trust PZ on biology, but I wouldn't incredulously accept legal advice from him. So, maybe reliable for physics/space, but unreliable for biology is my guess?

http://scienceblogs.com/pharyngula/2013/07/02/the-mfap-hypot...