Everybody’s Doin’ It

There is a new article in Science about rishathra. It seems that Neanderthals mixed with anatomically modern humans three separate times, AMH mixed once with Neanderthals, Neanderthals with Denisovans, Denisovans with something very old and also with Melanesians.

There are some implications: since Melanesians have a subset of the Neanderthal alleles carried by other Eurasians (while the Chinese have a superset), the chance that the Melanesians are, at least in part, the product of a an earlier expansion is increased. As a friend said, the posterior is bigger. This friend is apparently a devotee of both Bayes and Sir Mix-a-Lot.

This brings up the perennial question: what was it like? We’ve all read the usual speculation about a human girl (anatomically modern in all the right places) who, while bathing, encounters a Neanderthal dude returning from a successful hunt, with the striated muscles of his bronzed torso exposed for anyone to see. Even if his verbal skills are limited (old version of Foxp2), maybe he’s a good dancer (Puttin’ on the Ritz). One thing leads to another, until at last his near-manhood can no longer be denied. Romantic, kinda.

But sister species can remain interfertile for a surprising long time, often for a couple of million years, sometimes longer. And some of our hominin cousins diverged very far in that time. For example, Homo naledi may not be all that old: we’re looking for a source of some very divergent DNA in Pygmies and Bushmen, and H. naledi is a possibility – but an embarrassing one. I mean, they had a brain the size of a grapefruit. Same with the Flores hobbits. We’re talking Stinking Lizaveta here.

Advertisements
This entry was posted in Uncategorized. Bookmark the permalink.

33 Responses to Everybody’s Doin’ It

  1. The posterior is larger…. rampant Bayesianism.

  2. Sandgroper says:

    For the Neanderthal interbreeding, I always imagined it would have to be a Neander male ambushing/overpowering an AMH female because (1) I couldn’t imagine an AMH male overpowering a Neander female, and (2) the child would need to grow up in an AMH group, otherwise it would die out with the other Neanderthals and leave no trace in the genomes of those of us who carry Neander ancestry.

    As for the other mixes, we have no idea what Denisovans looked like, and I just don’t want to think about H. naledi or floresiensis. I had a friend from the Dominican Republic who swore blind that some men there rape chickens ( which is always fatal for the chicken), but I don’t want to think about that either. Some permutation of H. erectus just seems more likely to me – subcranially, they weren’t that different.

    • AnonymousCoward says:

      5 years from now, when Naledi admixture in pygmies has been confirmed beyond doubt, Pak Protector Greg will have moved on to something even more horrific, like the retroviral origins of gender dysmorphia from prehistoric chickenrapists. Yet another round of denouncements for rustling jimmies will be directed at him, and ignored. A few years later, the chicken rapist will be filmed using time traveling cameras, and Greg will at that time be explaining his new hypothesis that we’re all descended from retard-baby-fish.

    • epoch2013 says:

      Also, there is no Neandertal mtDNA among us, nor Y-DNA. So the introgression may have been via AHM women whose male offspring was infertile.

      • Rick says:

        That makes the most sense. But the children surely weren’t infertile.

        I am gonna go far out here and suggest that the first hybrids were not so messed up. They were probably bigger and stronger than the other AMH. And not particularly dumb either.

        If this was super common, then we would see a much larger range of values, not 3 or 4, or even just 10 events. So if a 1 in 10,000 event left such a huge legacy of 3% of the genome (and 6-7% in some places), then there was clearly a huge selection for keeping around some of the new genes right from day one.

        These are huge selective sweeps, but it is too far back to tell what the selection was driven by.

        I have connected with maybe 100 4th cousins on 23and lme and FTDNA and Ancestry. Most of us share 0% IBD stretches.

        Most people inherit 0% from most of their 5th great grandparents.

        Either there was massive selection, or this was a meeting of two larger groups that totally fused. And then this happened again later.
        Several of the Neanderthal genomes had the AMH versions of FoxP2, so after the very first event, the language stuff probably became less of an issue.

      • rkr says:

        I’m not sure that there are absolutely no Neanderthal or Denisovan uniparental lineages out there. If there are, they would be in isolated locations or just scattered across large populations at a frequency which makes them effectively invisible.

        • Rick says:

          Well. There are already several million tests with zero positive results… I won’t hold my breath with modern samples.

          Maybe some ancient humans will have one.

    • j says:

      Chickens are “hot” (high temperature).

    • Paul Mendez says:

      Sex with donkeys is evidently considered an appropriate outlet for unmarried males in some parts of rural Columbia.

  3. MawBTS says:

    I once spent a long time trying to puzzle out the meaning of the cover to the The 10,000 Year Explosion.

    Were the yellow humanoids Denisovans? The blue ones AMH? Do the overlapping figures represent a mating event? Etc.

    Then you revealed that the cover means…absolutely nothing at all.

  4. AppSocRes says:

    This may be a very stupid question but please bear with my ignorance: Is there any good reason why different environments affecting the different human populations we are talking about couldn’t have resulted in such strong selection against or favoring different Neanderthal DNA fragments that the observed differences are actually not due to interactions with Neanderthals at different times but to one interaction with selection ultimately resulting in three very different patterns of Neanderthal DNA in populations that have undergone thousands of years of differential evolutionary pressures?

    • Dale says:

      My understanding is that a solid majority of the single-nucleotide changes that are fixed are neutral, they don’t affect the protein sequence. So if you watch those, they tell ancestry, not selection history.

    • gcochran9 says:

      Most things are neutral – selection doesn’t much change the overall ancestry fraction one way or the other.

  5. epoch2013 says:

    @gcochran9

    You mentioned before you estimated AMH-Neandertal hybrid infertility would be small because the split was rather recent. However, I keep reading the Sima de los Huesos genomes push that split back. Do you think that increases the possibility of (partial) male hybrid infertility?

  6. Rick says:

    “H. naledi is a possibility – but an embarrassing one. I mean, they had a brain the size of a grapefruit. Same with the Flores hobbits.”

    How can you conclude that brain size is directly related to intelligence?

    People with achondroplasia have much smaller brains than a normal sized person, yet they have an average IQ of 96. (See Jyoti Amge as an example. She is only 2 feet tall and I have definitely seen grapefruit larger than her head).

    Neanderthals had larger brains, but you assume they were less intelligent.

    Not that this has much to do with makin’ babies… Intelligence seems to slow that process down.

    • gcochran9 says:

      People with achondroplasia have larger-than-average brains. Obviously big heads. But also problems with compression of the spinal cord and brain stem, etc.

      I think that brain size is directly related to intelligence because it is. Although size isn’t the only factor.

      • Rick says:

        So we agree, size is clearly not the only factor. Not is intelligence when it comes to long term selection, unless you follow a single gene path. Any Homo erectus could have been just as smart as modern humans with just 3-5% gene introgression. The reason for the modern ratios are probably because of drift in the other genes. AMH had a larger population size.

  7. Dale says:

    Is there any known history of the chromosome rearrangements in the history of Homo? My understanding is that fertility reductions are more a matter of chromosome rearrangements than the accumulation of different genes.

  8. Ursiform says:

    “The fact that she is a woman is half the battle.”

  9. IC says:

    Biology might be random drift of every thing (genes, migration, mating, selection).

    When the drift fits, it stays. If not, gone.

    • IC says:

      Certainly behavior drift.

      • IC says:

        Like genetic mutational drift, behavior drifts are mostly harmful like those patients with psychosis. Delusion, paranoid, grandiose, major depression, ect are all pretty harmful and cause less fit behaviors which are limited by natural selection.

        However, moderate grandiose delusion can produce unwavering confidence in some people, which might be very fit in some political environment. Certainly too much of it will end up in psychiatric wards.

        Physical hurts cause pain and suffering feeling in most people. Drift in this can have delusional happiness in physical hurt (algolagnia). Such unfit delusional feeling is unfit and can cause someone’s life. But when it happens at right spot (genital region), it encourages reproductive behavior, more descendants and is very fit. Thus a delusional feeling (pleasure from rubbing mucosa) become fixed as sexual pleasure and normal in descendants. Origin of sexual pleasure.

        Certainly all these drifts have genetic basis. Process is random. Result is not. Only fit one stays.

  10. TWS says:

    Yikes! Reading the wiki article on Homo naledi makes me wonder why it’s even in the homo genus at all. They were certainly primitive little buggers with bodies not really adapted yet for full upright walking and fingers still curved for climbing. I wonder if the population in the cave aren’t some kind of hybrid?

    What other candidates are proposed for the Pygmy archaic mixture? What percentage Archaic are Pygmies?

  11. Sid says:

    Is there any evidence that AMH mated with homo erecti in Asia? Maybe the Denisovans killed off most of the the latter.

  12. That could explain some interesting data. Razib Khan conjectured that admixture could be a part of why their divergence estimates are so far back http://www.unz.com/gnxp/the-blood-of-the-first-men-runs-thin-in-our-kind/

    Moreover, Lynn has measured the pygmy IQ at 53 and estimated the San IQ at 54. Even if these numbers were off by an entire standard deviation, they would still be pretty striking. I expect, as you seem to, that admixture likely has something to do with that.

    In any case these data hammer the point through my skull that introgression is probably the primary means by which new genes are added to hominin populations, and has been for a long time.

  13. RJW says:

    Any word on Henry?

  14. SamGamgee says:

    You have such a distinctive pedagogical style. Kind of like the Discovery channel meets Adult Swim.

  15. Harold says:

    The “Puttin’ on the Ritz” link needs fixed.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s