Neuroanthropology

For a greater understanding of the encultured brain and body…

Your Great x 2360 Grandpa was a Neanderthal!

Posted by Paul Mason on October 26, 2010

Is your Dad the descendent of a Neanderthal? Visit our PLoS website to find out more. 

Recent evidence has shown that a small percentage of human DNA is Neanderthal. This Neanderthal DNA entered the human gene pool between 80,000 and 50,000 years ago.

While human DNA may contain traces of Neanderthal ancestors, mitochondrial DNA from Neanderthals has not been found in humans. Mitochondrial DNA comes uniquely from your mother. Is it plausible that male Neanderthals were able to mate with female humans, but that the reciprocal cross was unable to occur?

Analyses of the Y chromosome suggest that we share a common male ancestor 59,000 years ago. Could this male ancestor have possibly been Neanderthal?

If our common male ancestor is neanderthal, and considering that the Y chromosome is transmitted uniquely through the paternal line, could it mean that men are more closely related to Neanderthals than women? Have men and women truly come from two different species?

Visit the full post on our PLoS website for the full explanation of this intriguing hypothesis.

8 Responses to “Your Great x 2360 Grandpa was a Neanderthal!”

  1. [...] You: Your Great x 2360 Grandpa was a Neanderthal! (neuroanthropology.net) [...]

  2. Mellie said

    This is daft. We don’t have a single ancestor, we are the product of generations of evolution and we are also the product of both sexes.

    “African Eve” is a stupid idea for the same reason.

  3. Paul Mason said

    Hi Mellie, It’s great to see people engaging with scientific data! This post is just to send our readers through to our PloS website with a whole bunch of thought-provoking questions. As you correctly suggest, the human lineage is not unilineal but somewhere our family trees cross over. It would be intriguing to think that they cross over at the offspring of a Neandertal. I’ve heard of a study that demonstrated that everyone in France is somehow related to Charlemagne, and other research showing that everyone in Europe has mtDNA related to Genghis Khan. Technically, there was a very slim chance that the Neandertal Y chromosome entered the human gene-pool, but the offspring of a Neandertal-Human cross may have has more success at passing on their genes.

  4. ohwilleke said

    Given that the one thing we know about Neanderthal autosomal DNA is that it is more common in ancesteral Eurasians than it is in Africans, presumably the Neanderthal Y-DNA would have to have been the basal individual in the Y-DNA haplogroup CF line (which is distinguished from the DE line by the YAP mutation). This would also mean that the phylogenetic roots of the Y-DNA tree, which includes “Y-DNA Adam” who is the most recent common ancestor of all modern humans, and Y-DNA haplogroups A and B (found mostly in Khoisan and Pygmy populations in Africa) would have to be ancesteral not just to Y-DNA CF and Y-DNA DE, as current phylogenies assume, but also to Neanderthals.

    Given that mutation rate estimates put the emergence of Y-DNA A, B, CF and DE haplotypes no later than ca. 70,000 to 100,000 years ago, that Y-DNA Adam dates back presumably to ca. 200,000 years ago or more in Africa, and that Neanderthals date back to ca. 300,000 to 500,000 years ago, even gross errors in calculating ages from the number of Y-DNA mutations (and most of the critics argue that the conventional dates are too old, not too young), the time lines just don’t match up. Even at a very, very slow Y-DNA mutation rate, you would expect far more mutations between Neanderthal Y-DNA and any modern human than exists to distinguish any two living modern humans today if admixture took place wihtin the last 100,000 years.

    One also would have to explain why some notable Neanderthal traits with adaptive advantage (e.g. like skin color) didn’t survive in the Neanderthal descendants and instead were developed via convergent evolution with different genetic sources.

    There are easier way to come up with a society with 1% to 4% Neanderthal DNA in Eurasians, yet no discernable Y-DNA or mtDNA lineages from Neanderthals. First, one infers that Neanderthal/human hybrids were children of infrequent and brief liasons (perhaps during periodic meet ups of human and Neanderthal tribes for trade, and at any rate for periods of less than nine months) or less romantically rapes, rather than sustained relationships, and that the children ended up in the mother’s tribe and not the father’s as a result. Children of Neanderthal mothers ended up in Neanderthal tribes and their descendants died out with the rest of the Neanderthals. Children of modern human mothers ended up in modern human tribes and their descendants survived to become about 2% of the future Eurasians (they were probably small in number but introduced when the founder population of Eurasians was quite small). Thus, no surviving Neanderthal descendants in modern human populations would be expected to have any Neanderthal mtDNA.

    Then, you would have to suppose that men who were half-Neanderthal or one-quarter Neanderthal suffered significant selective disadvantages that were not suffered by women who were half-Neanderthal or one-quarter Neanderthal. Maybe their deficiencies in tool making and hunting style and hunting team work made them poor prospects as husbands, relative to modern humans, for example, or perhaps they lacked the social skills needed to win a modern human mate. But, perhaps hybrid Neanderthal women were considered acceptable as brides and members of the tribe more readily, because expectations of female early modern humans were more attainable for Neanderthal hybrid women. Also, if the Eurasian founding group into which Neanderthal autosomal DNA gets injected is small enough (e.g. 500 women of child bearing age, a total population of about 2,000 people at the time of Neanderthal contact), one can imagine simply random chance coming into play. Maybe there were only five admixture events between Neanderthal men and modern human women and those events produced a disproportionate number of girls, simply as a matter of random chance, leaving only one or two half-Neanderthal men, and those men happened to have no male descendants who lived to reproduce at some point in the first one or two or three generations for reasons that had nothing at all to do with selective advantage. This isn’t the most probably outcome, but if the numbers are small enough, it isn’t vanishingly improbable and it would fit the facts. Sometime improbable things happen. And, selective advantages of full blooded modern human men v. hybrid modern human men in modern human commmunities could tip the odds of random chance a little even if they were strongly selective enough to make the outcome a foregone conclusion. Indeed, evolution itself depends upon improbable things happening every once and a while.

  5. Paul Mason said

    Ohwilleke, thank you for your thoughtful reply and great ideas. I am encouraged by the excitement that our post has received. I hope that our readers take the time to think about the various scenarios you propose.

    Our post over at PLoS Blogs is more comprehensive and explains the biology behind interspecific hybridity and Haldane’s Law in mammals. The post here on our old website is really just to lead people over to the new site at PLoS Blogs.

    Although it is exciting to suppose that our common grandfather was the offspring of a Neanderthal-human cross, I agree with you that it is highly unlikely. The most enticing piece of data that we raise in our PLoS Blog post is that there is a substantial amount of nuclear DNA from Neanderthals in the human gene pool (the equivalent contribution of one great-great-great Neanderthal grandparent to any one human), but there is an absence of any mitochondrial DNA from Neanderthals. These observations can be explained by mechanisms of interspeficic fertility. I am currently working on this hypothesis with Professor Roger Short — a specialist in reproductive biology. If there were no biological mechanisms that could explain the phenomena we observe, we would be in a difficult place because we know so little about Neanderthal and human social behaviour of that period, and we have to be careful about the assumptions we make.

    The biology behind interbreeding is fairly solid and the presence of Neanderthal nuclear DNA in the absence of mtDNA is a convincing artefact in humans that can be direclty related to known mechanisms of reproductive biology. For example, recent studies show that girls are more likely to survive a stressful pregnancy. Neanderthal births were not easy. Furthermore, if girls were more likely to survive a pregnancy then we would expect more girls than boys in the hybrid population. A lack of Neanderthal mtDNA in the hybrid population leads to the conclusion that the mother was a human, not a Neanderthal.

    Do you work in this area? You make some very insightful comments. I particularly liked the suggestion that “Children of Neanderthal mothers ended up in Neanderthal tribes and their descendants died out with the rest of the Neanderthals.” These ideas are exciting to think about but we have to be careful about making assumptions about Neanderthal social and cultural behaviour, or even the human socio-cultural behaviour of the time. But if we indulge in our imagination, we could also suppose that if a female Neanderthal was impregnated by a male human, then she may have been forcefully exiled from her group. Could a lone female Neanderthal be accepted by a human group or would she have been shunned? Alternatively, were female Neanderthal and male human liaisons simply uncommon because the robust female Neanderthal successfully resisted the advances of the gracile male human?

    Another fascinating hypothesis you propose is that “men who were half-Neanderthal or one-quarter Neanderthal suffered significant selective disadvantages that were not suffered by women who were half-Neanderthal or one-quarter Neanderthal.” I don’t know why we would “have to suppose” this scenario, and there are probably arguments for the alternative hypothesis. Perhaps we could draw up a post with a list of scenarios…

  6. Puneet said

    I’m not up with the biology of the situation, but the analysis is cool!

  7. ohwilleke said

    “Do you work in this area?”

    No. I’m a Denver lawyer.

  8. [...] More reading: SvD , Wired Science, Was your grandpa a Neandethal? [...]

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