6 ms·

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

by Steuard 13y 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.)

grey413 13y 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.
- Steuard 13y 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.
  - ghkbrew 13y ago
    In general I agree with you, it's an extraordinary claim with less than extraordinary proof to put it mildy. However I thought I'd make one small correction on your genetics. > 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.
    - Steuard 13y ago
      Thanks! I didn't realize that recombination was so frequent. I'm glad to have a better sense of that now.
  - Houshalter 13y ago
    I don't see why it's that implausible. You are descended from almost every single human being alive 1,000 years ago. Can you find any significant amount of DNA contributed from only a single one of your ancestors? 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.
    - grey413 13y ago
      Evolutionary geneticists don't trace individual lineages that far out, nor would they need to. The hypothesis under question is that the porcine/proto-hominind cross provided a variety of important, wide-acting traits that all humans share. That means that every human has them, and that every chimpanzee doesn't have them. That would show up in a comparative genomic assay.
    - 13y ago
marshray 13y 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-evidence.html http://phys.org/news/2013-07-human-hybrids-closer-theory-evi...

by Steuard 13y ago

grey413 13y 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.

Steuard 13y 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.
- ghkbrew 13y ago
  In general I agree with you, it's an extraordinary claim with less than extraordinary proof to put it mildy. However I thought I'd make one small correction on your genetics. > 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.
  - Steuard 13y ago
    Thanks! I didn't realize that recombination was so frequent. I'm glad to have a better sense of that now.
- Houshalter 13y ago
  I don't see why it's that implausible. You are descended from almost every single human being alive 1,000 years ago. Can you find any significant amount of DNA contributed from only a single one of your ancestors? 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.
  - grey413 13y ago
    Evolutionary geneticists don't trace individual lineages that far out, nor would they need to. The hypothesis under question is that the porcine/proto-hominind cross provided a variety of important, wide-acting traits that all humans share. That means that every human has them, and that every chimpanzee doesn't have them. That would show up in a comparative genomic assay.
  - 13y ago

marshray 13y 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-evidence.html http://phys.org/news/2013-07-human-hybrids-closer-theory-evi...