Neanderthals: Intimate Strangers

For my new “Matter” column in the New York Times, I look at the latest advance in our understanding of Neanderthal DNA. Neanderthals and humans interbred about 40,000 years ago, and their DNA is still in human genomes today. Scientists are mapping those Neanderthal genes we carry, and figuring out which ones have benefited us and which have made us sick.

One thing I didn’t have room to discuss is a question that I keep asking and to which scientists always respond with intriguingly noncommittal answers: Are Neanderthals members of our own species? Are they Homo sapiens? Are they a subspecies–Homo sapiens neanderthalensis? Or are they a separate species–Homo neanderthalensis?

For much of the 1900s, many scientists saw Neanderthals as the ancestors of living Europeans. But then in the late 1900s, some researchers argued that living humans descended from a small group of Africans that expanded out to the rest of the world. The discovery of Neanderthal DNA has wonderfully muddled that dichotomy. Humans and Neanderthals, the DNA suggests, share a common ancestor that lived 600,000 years ago. After hundreds of thousands of years, they came into contact and interbred. The fact that we carry some Neanderthal DNA shows that their hybrid offspring could have children of their own. One could argue that this ability to breed means that we belong to the same species. Perhaps we’re just subspecies that came to look different because we adapted to different conditions–Africa versus Eurasia.

But the latest evidence adds a new twist. Many genes from Neanderthals appear to have reduced the number of offspring that hybrids could have. That would explain why big segments of the human genome are free of Neanderthal DNA.

Why these genes were harmful isn’t yet clear, but the clues are fascinating. Take FOXP2, a gene involved in language in humans. Neanderthals have FOXP2 as well, but natural selection appears to have eradicated their version from the human gene pool. Did humans with the FOXP2 have trouble speaking? There are other clues that Neanderthal genes created infertile male hybrids. These effects didn’t have to be catastrophic to lead to the disappearance of Neanderthal genes. They might have just eroded away over many generations.

There are no known reproductive barriers between any living humans, no matter how distantly related they are to each other. These barriers are crucial to the origin of new species (although they can still allow some populations to interbreed even after millions of years). So perhaps we can say that Neanderthal, while not a separate species, were well on their way to separating.

15 thoughts on “Neanderthals: Intimate Strangers

  1. Don’t expect this “science” to sneak its way into the classrooms here in the South. Our Lord and Savior made it very clear there is no way we evolved from these savages. Tennessee has passed the Monkey Law legislation which ensures teachers can challenge these so-called scientists and their twisted research funded by the liberals in Washington. Read about how we’re keep Christ in the Classroom at

  2. I did not know about the evidence that there were possible genetic ‘islands’ of reduced fitness in human-neanderthal hybrids. It seems preliminary, but right now your last sentence seems to be be where things should stand right now. So I would agree that we and neanderthals represent different subspecies of H. sapiens.

  3. You’re right, Brandt, we didn’t. We share a common ancestor with them and later, some populations of anatomically modern H. sapiens interbred with some populations of H. neanderthalensis and…

    What am I doing? You don’t CARE. It does bug me, though, is that you’re calling them “savages,” which is just…that says so much more about you than the Neanderthals.

  4. You fail to mention that Neanderthal DNA has conferred advantages to modern humans typically pertaining to skin and hair:

    Neanderthal Influence on Skin, Hair, Common Diseases

    Despite their different approaches, both teams converged on similar results. They both found that genes involved in making keratin—the protein found in our skin, hair, and nails—are especially rich in Neanderthal DNA.

    For example, the Neanderthal version of the skin gene POU2F3 is found in around 66 percent of East Asians, while the Neanderthal version of BNC2, which affects skin color, among other traits, is found in 70 percent of Europeans.

  5. I suspect Mr. Hardin may well be being facetious.
    Although I find it amusing that Tennessee seems to be in a rowboat desperately rowing against the tsunami of knowledge coming from the vast ocean that is science.
    Pray as much as they wish, deny as much as they want, clutch their crosses and close their eyes to the truth and facts for as long as they desire, they will be crushed by it in the end.

  6. I am a southerner (by birth), Christian (by choice), and a scientist (by profession). As a teacher in Alabama (physics, Auburn University), I have been fighting the likes of Mr. Hardin for half a century. My prayer remains, “from such as he, dear Lord, deliver us!”

  7. Don’t worry, Mr. Hardin. When all the jobs leave your states for China, India, northern US states, and other such places with work forces competent in basic scientific concepts, our tax dollars will still support your welfare checks.

  8. I think the first comment was intended as sarcasm. At least I’m hoping so. Wow…but maybe it’s not? Now that would be worthy of anthropological research.

  9. The Amphiox comment is not sarcasm. Without science understanding, the only jobs left will be for hewers of wood and drawers of water.

  10. If two populations of extand mammals or birds interbred, but gene flow is seriously reduced due either to post-zygotic (e.g. hybrid quasi-sterility in the heterogametic sex, male for mammals and female for birds) or prezygotic (e.g. a strong (statistical) preference for partners of the same population) they will usually be considered as different species. In the sapiens X neandertal case, you should certainly add a cultural barrier, and the hybrids were certainly rare and probably socially more or less ostracized (the situation described in the fictional “Earth’s children” by J.M.Auel seems quite realistic from this point of view). That didn’t prevent introgression of “good” or neutral neandertal genes into sapiens populations – and even, by genetic drift, of some “not so good” ones. But, except for some “politically correct” reasons, I do not see why they should not be considered as different species, as we do with gulls or carrion and hooded crows for example. It’s gene introgression, not a general melting.

  11. I have a simple question – unequivocally, how many chromosome pairs did Neanderthals have. Humans obviously have 23, but I wonder whether Neanderthals had 24 (like gorillas, chimps and orangs) or 23 like us. Any answers to this?

    1. @mark jacobs
      Denisovan had 23 pairs according to Meyer et. all (Science 338, 222-226). As Denisovans are closer to Neanderthals than to modern humans, it is logical to postulate than Neanderthals had 23 chromosome pairs too. The fusion giving our chromosome 2 is probably very old.

  12. Your Neanderthal picture looks remarkably like Martin Amis. He was a close friend of Christopher Hitchens of course. Neanderthal/Homo Saps romance – the ultimate Romeo and Juliet tragedy?

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