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0 pointsgiardini11y ago0 comments

Humans and gorillas? What about our ancestors and those of pigs? I found this hypothesis fascinating:

"A chimp-pig hybrid origin for humans?"

http://phys.org/news/2013-07-chimp-pig-hybrid-humans.html

from the article:

" I asked McCarthy if he could give a date estimate for the hybridization event, he said that there are a couple broad possibilities: (1) It might be that hybridization between pigs and apes produced the earliest hominids millions of years ago and that subsequent mating within this hybrid swarm eventually led to the various hominid types and to modern humans; (2) separate crosses between pigs and apes could have produced separate hominids (and there's even a creepy possibility that hybridization might even still be occurring in regions where Sus and Pan still seem to come into contact, like Southern Sudan)."

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Steuard11y ago

That's one of the most ridiculous things I've ever read. We've done genetic studies on humans and apes, and we share some huge fraction of our genome with them (99%+, right?).

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.)

grey41311y ago

The champion of the theory attributes the lack of genomic similarity to repeated back-crossing to one of the parent populations. To put it in other words, the droplet of initial hybridization got diluted in the larger gene pool, but the novel genes (and thus traits) remained and underwent selection.

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.

Steuard11y ago

I saw that claim in the article, yes. I'll admit that I don't know enough about genetics to make strong claims here, but it doesn't sound remotely plausible to me. He wants to simultaneously claim that 1) hominids got so much porcine DNA that they have lots of substantial, recognizable anatomical features as a result, and 2) hominids have so little porcine DNA that it's all but invisible in our genetic code.

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.

2 more replies

marshray11y ago

Eventually though, sufficient data will fall from the collisions between example-fed discussion and informed search to deliver an elevated consensus. One particular approach recommended McCarthy is in silico chromosome painting of the human genome with random pig and chimp sequences in an effort to find hotspots of similarity to pig.

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

saalweachter11y ago

Basically, no.

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.

marshray11y ago

I think he's saying relatively modern chimps and pigs may have had a hybridization event.

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...

saalweachter11y ago

No.

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...

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tokenadult11y ago

That hypothesis is completely wrong:

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

Noishe11y ago

There isn't enough attention to this in my opinion. When you research it, everything lines up so nice.

j / k navigate · click thread line to collapse

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Steuard11y ago

That's one of the most ridiculous things I've ever read. We've done genetic studies on humans and apes, and we share some huge fraction of our genome with them (99%+, right?).

grey41311y ago

Steuard11y ago

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.

2 more replies

marshray11y ago

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

saalweachter11y ago

Basically, no.

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

marshray11y ago

I think he's saying relatively modern chimps and pigs may have had a hybridization event.

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

saalweachter11y ago

No.

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...

1 more reply

tokenadult11y ago

That hypothesis is completely wrong:

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

Noishe11y ago

There isn't enough attention to this in my opinion. When you research it, everything lines up so nice.

j / k navigate · click thread line to collapse