Neandertal population structure

By Razib Khan | February 26, 2012 6:04 pm

There’s a new paper out, Partial genetic turnover in neandertals: continuity in the east and population replacement in the west. The primary results are above. Basically, using 13 mtDNA samples the authors conclude that it looks as if there was a founder effect for Neanderthals in Western Europe ~50 K years ago, generating a very homogenized genetic background for this particular population before the arrival of modern humans. Perhaps it’s just me, but press releases with headlines such as “European Neanderthals Were On the Verge of Extinction Even Before the Arrival of Modern Humans” strike me as hyperbolic. I’m also confused by quotes like the one below:

“The fact that Neanderthals in Europe were nearly extinct, but then recovered, and that all this took place long before they came into contact with modern humans came as a complete surprise to us. This indicates that the Neanderthals may have been more sensitive to the dramatic climate changes that took place in the last Ice Age than was previously thought”, says Love Dalén, associate professor at the Swedish Museum of Natural History in Stockholm.

There are several points that come to mind, from the specific to the general. First, from what I gather Neandertals were actually less expansive in pushing the northern limits of the hominin range than the modern humans who succeeded them. From this many suppose that despite the biological cold-adapted nature of the Neandertal physique they lacked the cultural plasticity to push the range envelope (e.g., modern humans pushed into Siberia, allowing them to traverse Beringia). One might infer from this that Neandertals were more, not less, sensitive to climate changes than later human populations. Second, there is the fact that as the northern hominin lineage one would expect that Neandertals would be subject to more population size variations than their cousins to the south during the Pleistocene due to cyclical climate change. This is not just an issue just for Neandertals, but for slow breeding or moving organisms generally. The modern human bottleneck is in some ways more surprising, because modern humans derive from a warmer climate. Finally, there is the “big picture” issue that though we throw these northern adapted hominins into the pot as “Neandertals,” one shouldn’t be surprised if they exhibit structure and variation. Non-African humans have diversified over less than 100,000 years, at a minimum the lineages which we label Neandertals were resident from Western Europe to Central Asia for ~200,000 years. Wouldn’t one expect a lot of natural history over this time?

Presumably the authors focused on mtDNA because this is copious relative to autosomal DNA, making ancient DNA extraction easier. I’m a bit curious how it aligns with the inference from the Denisovan paper that Vindija and Mezmaiskaya Neandertals both went through a population bottleneck using autosomal markers. The dates from the paper’s supplements are not clear to me, though it seems possible that they may have sampled individuals where the Vindija population may have been post-resettlement. At some point presumably we may be able to get a better sense of the source population of the Neandertal admixture into our own genomes if the genomic history of this population is well characterized.

CATEGORIZED UNDER: Human Evolution, Paleontology
MORE ABOUT: Neanderthals
  • Onur

    None of the dates of the bottlenecked Western European Neanderthal specimens are prior to the modern human migration to Western Europe. The date of the Neanderthal bottleneck in Western Europe (<50,000 years before present) clearly coincides with the date of the appearance of modern humans in Western Europe (again <50,000 years before present) . It seems modern humans pushed Neanderthals to certain corners of Western Europe when they colonized Western Europe and this triggered a population bottleneck in Western European Neanderthals. Because that it would take longer for modern humans to colonize Eastern Europe with its harsh climate, Eastern European Neanderthals would preserve their earlier genetic structure longer.

  • http://forwhattheywereweare.blogspot.com/ Maju

    Nice map, it helps a lot to see the big picture.

    The only thing that this says is that the late West Neanderthals of Feldhofer, Vindija and El Sidrón were, matrilineally, descendants from a single population, which was distinct from their geographic predecessors of Valdegoba and Scladina but closely related to the “old school” Neanderthals from Italy. It can therefore be imagined that West and Central Europe were re-colonized from Italy (or maybe the nearby West Balcans).

    Instead Caucasian and Altaian Neanderthals retained their distinct lineages. We lack info from the late Southern Iberian Neandetrhals, which I would imagine more archaic than their continental neighbors (but just a guess).

    Feldhofer is characterized by a Micoquian culture (big almond shaped axes, often, but not in this case, intersped with Mousterian). Vindija and El Sidrón are both Mousterian. I say because I was kind of expecting this bottleneck to be related to Chatelperronian or other early UP techno-cultural expansion but there’s lack of data on that, I realize now.

    Whatever the case the appearance is of a population replacement by Neanderthals on other Neanderthals with an Italian or Balcanic source. As Onur says, it is at least curious that those dates are already within the probable time-frame of H. sapiens penetration in Europe: Istallosko, the earliest Aurignacian site, is 47.7 calBP, 44.3 BP uncal., with even older “aurignacoid” dates existing in Swabia and a number of other loosely “aurignacian” sites at the Pyrenees, South Germany, etc. before 45 Ka calBP.

    There is a modern (H. sapiens) individual dated to c. 55 Ka BP (OSL, stratigraphy) in Palestine (Emirian culture, considered precursor of other “aurignacoid” groups). So we must realize that Neanderthals were already interacting with “us” since very early, even in Europe itself.

  • Eurologist

    Not sure what is going on with this blog’s software, but my posts are no showing up. Another try:

    I have a hard time with the authors’ interpretation. It all hinges on a very small number of early western specimen, and their dating.

    If one believes the timing, there was an expansion of the tight group (blue in the figure) ~60,000ya. The other branches may very well have expanded, too – we have simply insufficient data prior to ~42,000ya.

    Now, all or nearly all of the finds of the tight group are dated to when AMHs were already present in the region. Since the expansion occurred well beforehand, I don’t see a bottleneck, but rather a very strong selection event. Could this group have had physiological features that spared them? Were they resistant to newly brought-in diseases?

    I also miss a discussion of the archeological context. Surely, instead of relying on the very few specimen we have, one should compare to known sites and occupation timings. IIRC, there indeed were expansions at some sites ~60,000ya and shortly before AMHs arrived.

    Interesting also that none of the tight group survived the Phlegraean Fields eruption…

  • Jacob Roberson

    I go into pop-sci articles expecting speculative scifi.

  • http://www.futurepundit.com Randall Parker

    ~50 years ago???

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    Since the expansion occurred well beforehand, I don’t see a bottleneck, but rather a very strong selection event. Could this group have had physiological features that spared them? Were they resistant to newly brought-in diseases?

    i don’t understand what you’re trying to say. you don’t consider a selection event a bottleneck?

  • Eurologist

    “you don’t consider a selection event a bottleneck?”

    Perhaps I am misunderstanding something here, but my reading of the authors indicates that they place a bottleneck just before the expansion @ ~60kya — ~15-20ky before what I see as a selection event. My argument is that while there may have very well been a contraction (expected ~70ka-60ka ago due to climate), there are noteworthy logical fallacies, here.

    Firstly, there is a strong ascertainment bias: the vast majority of specimen from which mtDNA has been extracted is of course the most recent material (<42kya).

    If, on the one hand, the analysis indicates a population expansion 60-50kya, but on the other hand we have almost no data from that time period nor from the time until 42kya, then we cannot say much about the makeup of the population during that time.

    Lacking that, a reasonable *conjecture* would be that *all* then-existing branches expanded – because the one that we *have* data from shows this pattern. Then, the only conclusion one is left with is that – although somewhat plentiful – all but the "blue" branch vanished with the arrival of AMHs. That's selection – not a bottleneck, at *that* time. And note – I am usually extremely cautious about selection.

    In other words, envision figure one with another pink and green and yellow tree (think "little boxes" song), similar to the "blue" lineage – except the other ones didn't make it past 42kya. It's like our Sun or planets or Saturn's ring syndrome: we are hardwired to initially think – based on a single data point – they are exceptions – until we realize they are not.

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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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