Anthropologist john hawks weblog uses a rather blunt stick to beat what’s at hints of the dominant but bogus “no-sex” class paradigm, and at worst plays to what could be called ancient racism. The issue? Genetic assays show that, thanks to interbreeding, modern humans have traces of Neanderthal genes… but no evidence of Neandertal genes in maternal mitochondrial DNA. If you want to skip ahead the last sentence reveals the problem.
I keep seeing people, who really ought to know better, saying that the new Neandertal genome results show that the gene flow must have been Neandertal men mating with modern human women, and not the other way around.
You see, they’re fixated on the idea that the mtDNA showed no signs that the Neandertal clade survived into the present-day population. That result really convinced some people that interbreeding was impossible. They’re flummoxed that some of the rest of the genome has significant signs of intermixture. It’s like their world is spinning out of control. I’m not naming any names, but if you’ve followed much of the press around the Neandertal genome, you’ve probably seen this suggestion.
I don’t know why it hasn’t occurred to them that the Neandertal mtDNA type was probably lost because of natural selection.
To avoid raising the awful specter of Darwin, they’ve been talking about weird mating restrictions. Well, I suppose that if you really have to find a way to get Neandertal nuclear genes into us, without bringing mtDNA along, a total lack of Neandertal women contributing genes is formally one way to get that.
I’d just like to see these people explain how exactly we managed not to get any Neandertal Y chromosomes, either.
If your biology’s a little shaky you just need to know the Y chromosome (which determines gender) is passed down only through male parents, mitochondria only by female parents. (X chromosomes are shared by both genders. They’re more easily mixed and so they’re not as helpful for determining geneology as mtDNA and Y chromosomes.)
Anyway, the point is that a) it’s really hard to explain how natural selection (itself a taboo topic) can winnow out genes and b) easy to play on stereotypes of prognathic cavemen dragging winsome and probably-unwilling modern-human women back to their caves and so given a choice? We’re going to get a lot more of the latter than the former.
So now we know why
Submitted by Nightfall (not verified) on Sat, 2010-05-15 18:26.So now we know why Neanderthals went extinct – inferior mitochondria!
Actually, I can think of another possibility. When closely related animal species hybridize, often you get rather different results based on which species is the mother and which is the father. (Witness tigons and ligers, or mules and hinnies.) Further, the offspring is usually sterile. Further note that human women have trouble giving birth in part due to their offspring’s large head size.
Assuming that they really are different species, but not quite different enough to be automatically infertile, it’s possible that a male human/female neanderthal hyrbid fetus ends up being oversized and usually fatal to the mother, and the neanderthal Y chromosome isn’t entirely compatible with the human X and results in either infertile offspring or a non-viable fetus which miscarries early in the process. So only the female offspring of a male Neanderthal and a female human is likely to survive and have children of their own.
Now granted, this is much less likely because it involves two sets of “ifs” instead of one, but it’s still theoretically possible.
I think Neanderthals had
Submitted by chingona (not verified) on Sat, 2010-05-15 22:43.I think Neanderthals had larger heads than humans. Don’t know about their pelvic openings. Ours is narrow (in a relative sense) because we walk upright. But so did Neanderthals.
Poorly worded, then. What I
Submitted by Nightfall (not verified) on Sun, 2010-05-16 03:39.Poorly worded, then. What I meant to imply is that possibly the entire fetus was too big, not just the head. (You ever seen a liger? Those things are huge, significantly bigger than either a lion or a tiger. Whereas the reverse mating, a tigon, is more normal-sized for a “big cat”. Having one particular sex-pair combination resulting in dwarfism or gigantism is not uncommon in animal hybridization.) Of course this is just idle speculation, there’s probably no way to know for sure.
Okay, but with humanoid
Submitted by chingona (not verified) on Sun, 2010-05-16 08:49.Okay, but with humanoid babies, it’s really the head that’s the thing. If you can birth the head, you can birth the baby. And the ligers may be huge, but there mothers manage to birth them, because they exist.
The issue of one combination possibly resulting in gigantism kind of misses the point of the post, though, which is that the absence of mitochondrial DNA is not really indicative of much, given that we also don’t have Y chromosomes.
nightfall, whats ur email
Submitted by Anonymous (not verified) on Fri, 2010-12-31 22:14.nightfall, whats ur email address? send an email to salemoregon4@gmail.com
salemoregon4, nope not an
Submitted by nightfall (not verified) on Fri, 2011-01-28 16:52.salemoregon4, nope not an expert on the specifics of cross mating of species, its just a guess from ligers and tigons as i stated and nothing more. try contacting a geneticist or biology professor
geneticist or biology
Submitted by whosnext (not verified) on Sun, 2011-02-06 21:20.geneticist or biology professor? did i miss something
There is one more
Submitted by fiveofnine (not verified) on Sun, 2010-05-16 05:09.There is one more possibility. These two species may not ever have come into contact much less mated. I don’t think anthropologist have ever found any fossils evidence of them existing in the same place at the same time. It is just conjecture.
My own conjecture. As xenophobic as humans are, I cant see them interacting with another species to produce enough relationships where their offspring’s DNA would even survive in the gene pool after many millennium.
On the other hand, people
Submitted by chingona (not verified) on Sun, 2010-05-16 08:50.On the other hand, people fuck dogs and sheep. Hard to think they would be above fucking a Neanderthal.
This is what I said; “ cant
Submitted by fiveofnine (not verified) on Sun, 2010-05-23 04:48.This is what I said; “ cant see them interacting with another species to produce enough relationships,” not that it couldn’t happen at all.
I might be wrong, but I don’t
Submitted by hmac (not verified) on Wed, 2010-05-19 21:51.I might be wrong, but I don’t think you have to invoke any selection on Neanderthal mitochondrial DNA to explain its absence in modern human populations. The presence of Neanderthal mitochondrial DNA would require an entirely female line of descendants from a Neanderthal mom – human dad pair. Insert even one intervening male generation in this tree, and the mitochondrial DNA is lost. The same thing is true for the Y chromosome, but for male descendants. I’m not sure about the statistics behind this, but it could be that, purely by chance, no direct female only line from a Neanderthal mom exists, and no direct male only line from a Neanderthal dad exists. Thus, only X chromosomes and autosomal chromosomes contain any evidence of our Neanderthal past. This is especially likely if the number of human-Neanderthal matings was very small. It is also possible that Neanderthal mitochondrial DNA exists in the human population, but no scientist has ever seen it, yet …
[Excellent point, hmac. The best analogy I’ve heard is that of cultures where last names are transmitted only through, say, the father’s side — every individual will obviously have a father (and half of his shared DNA) but a the name of a man who has only daughters will “go extinct” in just one generation without erasing anything else about him. If one of those daughters winds up in a society where names are all “inherited” from the mother… and then she has only sons, then her name “goes extinct” as well… all without changing the material fact that everything else about their ancestry is still as intact as if the offspring had been the “right” ones for passing on names. The selection part would still come into play with the rest of the shared DNA. —fl]