Study casts doubt on human-Neanderthal interbreeding theory

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When scientists discovered a few years ago that modern humans shared swaths of DNA with long-extinct Neanderthals, their best explanation was that at some point the two species must have interbred.


Now a study by scientists at the University of Cambridge has questioned this conclusion, hypothesising instead that the DNA overlap is a remnant of a common ancestor of both Neanderthals and modern humans.

When the genetic sequence of Homo neanderthalensis was published in 2010, one of the headline findings was that most people outside Africa could trace up to 4% of their DNA to Neanderthals. This was widely interpreted as an indication of interbreeding between Neanderthals and early Homo sapiens just as the latter were leaving Africa. The two species would have lived in the same regions around modern-day Europe, until Neanderthals died out about 30,000 years ago.

But Andrea Manica said the analysis had over-estimated the amount of shared DNA between Neanderthals and humans that could be explained by interbreeding. The analysis had not taken into account the genetic variation already present between different populations of the ancestors of modern humans in Africa.

“The idea is that our African ancestors would not have been a homogeneous, well-mixed population but made of several populations in Africa with some level of differentiation, in the way right now you can tell a northern and southern European from their looks. The mixing is not complete within continents.”

Taking these population differences, known as “substructuring”, into account for early humans living in Africa, Manica and his colleague Anders Eriksson worked out that modern humans and Neanderthals must have shared a common ancestor some 500,000 years ago and that the subsequent evolution of this species was enough to account for the DNA crossover.

Written By: Alok Jha
continue to source article at guardian.co.uk

19 COMMENTS

  1. Indeed you are. African humans (and now everyone according to this new study) contain 0% Neaderthal DNA, and it being primarily northern Europeans who had up to 4%. This study, as we just read claims those finding to be inaccurate, and no one has Neaderthal DNA, but in fact the origin is a common ancestor of both.

  2.  Well, he is and he isn’t. If the study is correct and the DNA in question is not Neanderthal but rather that of a common African ancestor, then that ancestral DNA should also be found amongst modern African populations. If it isn’t that would kinda blow the proposition out of the water.

  3. Well unless found to be faulty, it has already been ascertained previously that modern Africans do not possess this identifiable type of DNA whether the source is HSN or an ancestor of both HSN and HSS. I am not sure, but what it would technically mean if it is still considered true that if this DNA is not possessed by modern Africans, yet is a common ancestor of both… that would seem to imply that out-of-African humans are not HSS? Perhaps the reference to “sub-structuring” may indicate that in fact some, but not all, modern humans in the African region may contain this type of DNA.

  4. This would suggest that Southern populations diverged from a common ancestor with Neanderthals before Neanderthals and Northern Humans split.
    This would indicate that Neanderthals and Northern Humans continued to interbread to a point where they diverged sufficiently from the Southern Humans to develop the distinguishable DNA traits.

    It may be possible but seems unlikely.

  5. Here we go again Neutrinos travel faster than light. No they don’t. Astronomers find earth-like Gliese 581c exoplanet. No it’s not earthlike. Neanderthals interbred. No they didn’t. Coffee, chocolate, wine is bad, is good, is bad, is good, is bad, is good. Could be a Higgs boson. We’re not sure. Maybe. Possibility. Could be. Maybe not. 
    Is the pressure to publish so strong that speculative rather than more definite results have to fill up the news pages each day?
    “More research is needed”

  6.  “I am not sure, but what it would technically mean if it is still
    considered true that if this DNA is not possessed by modern Africans,
    yet is a common ancestor of both… that would seem to imply that
    out-of-African humans are not HSS?”

    Well exactly. And it would seem to me that such a proposition would be a lot harder to prove (not to mention the horrible racist can of worms it would open if modern Africans proved to be a different sub-species to everyone else) than the not unlikely possibility that European HSS interbred, from time to time, with HSN. Because if interbreeding did not happen, the question we ought to be asking is, “Why not?”

    If the DNA in question is indeed from a common ancestor, perhaps Homo Habilis or Homo Robustus, it should be found in all modern HSS, otherwise that ancestor would not be ‘common’ and modern humans would therefore not all be the same species. I am yet to hear anyone seriously suggest this possibility.

  7. Cook,

    Would you prefer that an interesting science story like this is kept in the dark unless some kind of official consensus is reached? I wouldn’t. I much rather hear about FTL neutrinos, even though such findings are often turned into silly headlines. The careful “more research is needed” disclaimer should be enough. Readers should realize that scientific research is a human effort with occasional errors and often awaiting further evidence. It is following the effort and missteps that bring science closer to the public, not memorizing dictated truths. Even if one isn’t a player himself, it’s like watching the game as opposed to hearing the end result a year later.

  8. Yeah, I know what you’re saying. Science a process, subject to falsification, with in built checks and balances, etc, etc. But on the other hand, I’d rather not waste 90% of my reading-time, reading tentative research that will be overturned in a year. Give me “Science Quarterly”, not ‘Science Monthly” or ‘Science Weekly” let alone “Science Daily”.

  9. I assume the original H.Sapien stock in Africa 200,000 years ago shared ~4% DNA with Neanderthals (from the common ancestor 500,000(?) years ago). About 60,000 years ago there was a migration out of Africa, and those H.Sapiens retained most of the shared Neanderthal genes, but the population who remained in Africa lost them (through evolution).  I can only assume drastic changes in African conditions resulted in ancient human genes being totally expunged in the African population, while those genes were still as good in the rest of the world as they were in Africa up to that time.

    I await the African fossils from 60,000, 50,000, 40,000, 30,000, 20,000,10,000 years ago showing the decline of Neanderthal DNA with baited breath.

  10. ” It may be possible but seems unlikely.”

    Not possible unless almost everything we think we know about Neanderthals is wrong.  Current thinking is that Neanderthals developed in Europe, descended from probably Habilis who left Africa long, perhaps hundreds of thousands of years, before evolution of Sapiens. Neanderthals and Northern Sapiens never split, they were never the same, they just happen to share an ancestral ‘grandparent.’

  11. I was wondering, since I don’t go to such nutty places, does the Creationist musuem in Kentucky, not only display dinosaurs with humans, but Neaderthals displayed as well — or, do they simply deny the past existence of Neanderthals period?  Oh, the world of nutty people with their own realities that do not match the fossil record.

  12. I think you have some wrong info here.

    Homo habilis was around about 2 mya and there is no evidence to suggest they are the direct ancestor of Neanderthals. Genetic
    evidence suggests the last common ancestor between HSS and HSN was around 500 kya which would suggest Homo heidelbergensis or Homo antecessor. There is a
    suggestion that HSS and HSN may have interbred as recently as 40-50 kya. The
    article suggests that there was no interbreeding but modern humans in north
    Africa share distinct DNA markers with Neanderthals. this would imply that
    there is a more recent divergence than between south African modern humans.

    Like I say, it seems unlikely. The most parsimonious explanation is that HSS and
    HSN exchanged genetic information relatively recently.

    It will be interesting to see the actual publication and see the upcoming paper by Svante Pääbo who adresses this suggestion.

  13. “Here we go again Neutrinos travel faster than light. No they don’t. Astronomers find earth-like Gliese 581c exoplanet. No it’s not earthlike. Neanderthals interbred. No they didn’t. Coffee, chocolate, wine is bad, is good, is bad, is good, is bad, is good. Could be a Higgs boson. We’re not sure. Maybe. Possibility. Could be. Maybe not. Is the pressure to publish so strong that speculative rather than more definite results have to fill up the news pages each day?”

    But science is all about the process of establishing what is true and what isn’t. I can’t think of anything better than seeing that process in action. It is precisely what shows people that science is ultimately all about evidence.

  14.  Ok, forget Habilis, should have checked that one. But the chronology you suggest agrees with what I’ve heard before, and with what I said. You say:
    “this would imply that there is a more recent divergence than between south African modern humans.”
    Would that then not also imply that either;
    a) Modern humans are not all one species. or,
    b) HSS evolved seperately in more than one place and at more than one time (a theory which did the rounds a few years ago, but which I understood had been pretty much dismissed by everyone in the field).
    “Like I say, it seems unlikely.”
    Agreed.
    “The most parsimonious explanation is that HSS and
    HSN exchanged genetic information relatively recently.”
    Which would also explain why, every time the temperature gets into the 20s,  sweat pours directly into my eyes from my inconveniently prominent brow ridges.

  15. Yeah points a) and b)
    are exactly what the article seems to suggest and as I say it seems very
    unlikely that this is true.

    The theory in point b
    you mention is called the multiregional hypothesis and accommodates the idea of
    gene flow and hybridisation but does suggest that there are regional traits
    that evolved due to periods of separation and adaptation to local environments.
    The opposing theory is known as the out of Africa theory and suggests that gene
    flow and hybridisation did not occur and that each “species” were the
    result of separate radiations out of Africa that replace existing inhabitants,
    it would fit more with the information in the article but not the research that
    suggests DNA similarities between northern HSS and HSN.

    It seems that a blending
    of these theories is something that must be looked at now. I admit it has been
    a while since I looked at the most recent research on this so not sure on the
    current status of this.

  16. I put some links on human lineage indicating time lines, on this earlier discussion:

    There was a similar article from the BBC, http://www.bbc.co.uk/news/scie… – based on an original article in Nature -  http://www.nature.com/nature/j

    The BBC version includes an interesting proposed Human lineage chart
    illustrating the relationships between the various Homo species.

    There are some alternative earlier lineage ideas presented in the National Geographic – http://ngm.nationalgeographic…. – also discussing A sediba.

  17. It is my understanding that this paper is merely a computer model of what COULD have happened to explain the DNA differences.  It does not, on its own, debunk the Neanderthal admixture hypothesis, whose evidence is stronger than this attempt at rebuttal.

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