Ancient DNA reveals how often and when humans & neanderthals interbred

Modern humans evolved in Africa around 195,000 years ago, but soon spread across the world. However, we weren’t the first species of human to leave Africa and we encountered other members of the human family on the way (like the Neanderthals). How we interacted with these other hominins is a fascinating topic. Did we trade and learn from each other? Did we fight? And it turns out we interbred with them; but that just raises a whole host of new questions. When? Where? How often?

DNA was recently recovered from a 45,000 year old human femur in Siberia (making it one of the oldest sources of modern human DNA ever); which may shed light on some of these questions1. In particular, how frequently were humans and Neanderthals actually interbreeding? Previous studies had estimated that the Neanderthal DNA in our genome could be explained by only a few dozen interbreeding events2; but this is really only a minimum figure. There could’ve been a lot more; with all that extra Neanderthal DNA being lost/diluted in the intervening tens of thousands of years.

The super-informative femur.

The super-informative femur.

So how much interbreeding was actually going on? I shan’t keep you in suspense: the Siberian femur confirms that there wasn’t actually that much interbreeding, containing a similar amount of Neanderthal DNA as modern Europeans. It would seem humans and Neanderthals studied each others biology (if you catch my drift) only a handful of times1. Neanderthals were not peacefully amalgamated into Homo sapiens. They almost all died. Sad times.

Whilst that’s the headline discovery from this really old genome the revelations don’t end there. So hold on to your DNA for a whirlwind tour of the other interesting things this femur has revealed.

First fun finding is that the amount of Neanderthal DNA in the Siberian femur is very similar to that of modern non-Africans (around 2 – 4%). 45,000 years of mutations, reproduction and demographic shenanigans hasn’t really altered it1. This strongly implies that we may now be reliant upon some of that Neanderthal DNA to survive; so it can’t be tampered with. On the other hand, despite living much closer to the interbreeding event a lot of Neanderthal DNA has already been lost in the Siberian; suggesting much of it may have been downright harmful and so natural selection quickly eliminated it.

Speaking of living closer to the interbreeding event, here’s the second fun finding. Sexual reproduction muddles up your genes and as a result of this our Neanderthal DNA has been spread throughout our genome; whilst most of that DNA in the Siberian femur is still clumped together. The researchers were able to use these differences to estimate when the interbreeding even actually occurred. Apparently we got funky with the Neanderthals ~60,000 years ago1. This is particularly interesting given we may have already met Neanderthals by 80,000 years ago3. Clearly it took a long time for early humans to come up with a good enough chat-up line to interest the Neanderthals.

The genomes of several people laid out next to each other. Yellow bits represent Neanderthal DNA. The Siberian femur is the top one.

The genomes of several people laid out next to each other. Yellow bits represent Neanderthal DNA. The Siberian femur is the top one, with the others being more modern individuals.

Moving swiftly on, the third fun finding is that the Siberian is more closely related to modern non-Africans than modern Africans. This would imply that modern non-Africans are descended from any subsequent migrations out of Africa. Those early pioneers who spread out of Africa is the same group modern non-Africans are descended from1. This probably isn’t a hugely significant in terms of human evolution; but as one of those descendants I find it really cool knowing all that amazing cave art might be part of my direct heritage.

And the final fun fact: This very informative Siberian was male1.

In short, a group of humans left Africa. Out in the wide world they encountered the Neanderthals; and after a little while getting comfortable interbred with them on a few rare occasions. This gave them a lot of genes that may have been harmful, but some which may have helped them survive. And survive they did, lasting all the way to the present day.


  1. Qiaomei Fu et al. 2014. Genome sequence of a 45,000-year-old modern human from western Siberia. Nature.
  2. Neves, A. G., & Serva, M. (2012). Extremely rare interbreeding events can explain neanderthal dna in living humans. PloS one, 7(10), e47076.
  3. Stringer, C. B., Grün, R., Schwarcz, H. P., & Goldberg, P. (1989). ESR dates for the hominid burial site of Es Skhul in Israel. Nature, 338(6218), 756-758.

6 thoughts on “Ancient DNA reveals how often and when humans & neanderthals interbred

  1. Pingback: Human evolution weekly update: Old DNA, old art and sexy men | EvoAnth

  2. No comments this round ?
    That cannot be allowed. Boredom could just possibly lead to more mischief .
    Firstly, thank you for the “news briefs you have now started. Much appreciated. Reading material.
    This post is such an interesting aspect of prehistory/evolution. Must be some kind of serious
    religious holiday in the rest of the world, occupying everyone that there are no comments!
    More questions than suggestions this round.

    Who exactly were the peoples that migrated from Africa 100 to 200,000 years ago? The “humans”?
    As I understand it, they moved to Europe, back to Africa and again back to Europe?

    In a small coastal town in South Africa, called Mosselbay ( bay of mussels) an American archeologist is/
    was heading a dig. Read somewhere, sometime, that he reckoned that at one stage, if I recollect
    correctly, approximately a 150,000 years ago, most of the human types of hominins had
    withdrawn to this spot on the globe as a result of climate change. Here they lived primarily
    on sea foods and as a result their IQ’s improved. If I remember correctly, there are very early signs
    of fire being implemented at this sight or in its locality. Some 70,000 years ago. Remember something about him saying there were very few human like hominins on the globe then. The sea had contracted 150km inwards at that stage and the local bio conditions were not conducive to an abundance of wildlife.
    It is an area that today still has more plant diversity than apparently the whole rest of the world.
    When the Europeans first landed in Africa they found peoples termed as “Strandlopers” ( Beach walkers)
    ( not beach bums) and “Hottentotte” ( tall, yellowish San type people) living on this southern coast of Africa,
    Quite distinctly a different type of human to the Negroids on a visual level.

    A question that arises with this movement of “early humans” out of Africa, who apparently came back as
    well (?) but did not spread the Neanderthal DNA here is;- who were they ? This, as there could have
    been a numbers of subspecies of “Humans” in Africa approximately 200 to 300,000 years ago. We
    know about the San who, if I remember correctly, have a different scull construction to Europeans
    and other peoples,the “Stranslopers”, the “Hottentotte”, the Pigmy’s in mid Africa as well as a people
    with 2 toes on there feet, adjusted to climbing trees ( Waduma ?) and then the Negroids. If there were others, who were the ones who actually left Africa, there would have been evidence that we, today,
    would know about.

    Next question then obviously is why, if the early humans did migrate back to Africa and had interbred
    with the Neanderthal’s, did they not distribute their DNA here?

    Next question could possibly relate to the above but of course I am not sure. Generally, I think, it
    is understood that Homo Erectus petered out in Europe around 1,2 to 800,000 years ago. In a
    course by Prof John Hawks I think I understood ( I cannot find the info again) that they survived in Africa until approximately 500,000 years ago. If this is correct, one wonders how it relates to the different groups of humans that developed in Africa. Especially if the San actually has a different scull configuration.

    That’s about it. Just wondering.

  3. Adam (or anyone else here),

    Can you expand on this at all, numerically I mean? :

    “…interbred with them on a few rare occasions. ”

    My wild just-to-get-the-ball-rolling guess is 1000 couplings. What do you think? I’m basing that on guessed populations for each group in the tens of thousands, and say a hundred individuals from each group (i.e., 1%) being interested in that kind of kinky, and doing it ten times each, on average. And let’s say 1/10th of those couplings resulted in fertile offspring. So 100 hybrids were born and got into everybody’s DNA.

    • The minimum figure calculated by a study into the subject is one interbreeding event every 77 generations or so over a period of 130,000 years. Which works out to ~70 interbreeding events. A very small number really.

      Of course the actual figure is probably much higher than this minimum, given that many lineages would likely die off etc. But even then we probably aren’t looking at much

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