By now, unless you live under a rock, you should have heard the news:
New genetic studies indicate that Neanderthals and modern humans likely interbred: Among the findings, published in the May 7 issue of Science, is evidence that shortly after early modern humans migrated out of Africa, some of them interbred with Neanderthals, leaving bits of Neanderthal DNA sequences scattered through the genomes of present-day non-Africans.
"We can now say that, in all probability, there was gene flow from Neanderthals to modern humans," said the paper's first author, Richard E. (Ed) Green of the University of California, Santa Cruz.
The results of the study have been published in two papers in the last issue of
Science (
Green et al. 2010,
Burbano et al. 2010 - both free access), where you can also
find a
free online feature. that provides some context to the public unfamiliar with genetics and/or Neanderthals To get a better idea of the significance and the nuts and bolts of this new work, you must, must go over to
John Hawks' blog for a very thorough discussion. I largely agree with his take on the reports and what they mean, but as I've argued elsewhere, we need to reconcile the genetics with the fossil, and especially the archaeological records. Just as there was a great deal of well-founded skepticism by some about 'X woman' a few weeks ago (something which I've been meaning to write about and hopefully will get to relatively soon), people need to come to grips with
all of the available data, as opposed to considering one line of evidence as trumping all others. In other words, it's not because some people wear lab coats that their data by definition trump all other!
In practical terms, I think this means that you will see a lot of people more sympathetic to a replacement position start arguing just that, that you need to reconcile these new genetic data with previous data that seemed to strongly support such a position (just how strongly is debatable, but besides the point here). Specifically, I think you'll see these people focus on caveats of genetic studies like they never have before, and
latch on to less parsimonious explanations of the genetics as 'something that needs to be considered seriously' (in this case, though, the
alternative interpretation is so much less parsimonious as to be untenable). Fundamentally, of course, there's nothing wrong with that; in fact, it's something I've argued for repeatedly both
on this blog and
in press (link to a free pdf on the Uluzzian). The key difference is that if people on both ends of the spectrum will (hopefully) begin playing by the same general rules.
Now, does this mean that it's time to do the Neanderthal victory dance (to quote Hawks) and to begin re-imagining the caves of Late Pleistocene Europe throbbing to the sweet rhythms of Barry White and Marvin Gaye? Well yes and no. Yes, there is no some fairly conclusive evidence that Neanderthals and modern humans interbred and yielded fertile offspring - this means that, from a purely biological standpoint, the two were part of the same species,
Homo sapiens. But no, it does not directly answer the question of how
and why Neanderthals ultimately disappeared. And also, NO!, "
Let's get it on" is not now a sufficient way of thinking about the relationships between Neanderthals and early modern humans!
That said, in my opinion, the two papers papers (Greene et al. 2010; Burbano et al. 2010) have the potential to considerably change how Neanderthals are discussed, both in terms of how people approach the data and how the data is interpreted, which are slightly different things. First, the people, namely researchers involved in modern human origins research. For one thing, as I mentioned above, you're likely going to hear much more frequent calls to consider all the evidence available and how it agrees/disagrees. On the other, in order to best incorporate all the relevant data in interpretations, the debate should shift away from 'one size fits all' interpretations to interpretations that are more regional in scale. Whether or not any of this actually happens is another story, but these papers definitely have the potential of serving as game changers in the modern human origins debate.
What I find most exciting about the Green et al. (2010) study is that it provides a strong boost for the importance of archaeological evidence plays in understanding the process by which Neanderthals disappear. Quite simply, this is because the genetic data and the skeletal evidence (Trinkaus 2007) now both converge to show some significant degree of biological interaction between the two homminin populations. The thing is, genetics and physical anthropology informing us about the fact that such interaction took place, but they tell us comparatively in terms of how these interactions played out. This is where archaeology comes in, since it's the only way we have of getting at the various types of interactions Neanderthals and modern humans might have had and to remove the preconceptions implicitly imposed by the notion that they were two distinct species.
In practical terms, we should now thankfully be moving away from models that see Neanderthals as fundamentally different from 'us'. This means that there is little reason to continue depending on interaction models that see Neanderthals as merely 'copying without understanding' whatever different behaviors early Eurasian modern humans might have displayed. An extension of that is that if Neanderthals and modern humans interacted enough for the former to have contributed between 1-4% of the genetic material of people of non-African extraction today, the two groups must have been able to interact in a sustained manner, which rules out a scenario whereby rape plays a preponderant role (and plays on prevalent ideas of Neanderthals as the savage/dangerous other). This also has implications about communication between the two groups, by which I mean that they likely were able to speak to one another, as already suggested by both
genetic and
indirect evidence anyway.
Perhaps most interestingly is that the degree of genetic contribution of Neanderthals to modern human genetics also sheds some light about how intense the interactions might have been, and also what some of the demographic parameters of thee encounters might have been. The numbers do point to some kind of demographic imbalance, though it must also be remembered that genes, like culture, can sometimes diffuse into an area much in advance of the arrival of a new population (Eswaran 2002, Eswaran et al. 2005). In other words, modern human genes might have made their way into Neanderthal areas by virtue of Neanderthal-hybrid interactions as opposed to necessarily only through Neanderthal-modern interactions. What this means for how 'hybrids' might have been perceived or integrated in either population is open to debate, but is a debate that might well shift to the center of ongoing debates about the nature of interactions between prehistoric humans populations.
ReferencesBurbano, H., Hodges, E., Green, R., Briggs, A., Krause, J., Meyer, M., Good, J., Maricic, T., Johnson, P., Xuan, Z., Rooks, M., Bhattacharjee, A., Brizuela, L., Albert, F., de la Rasilla, M., Fortea, J., Rosas, A., Lachmann, M., Hannon, G., & Paabo, S. (2010). Targeted Investigation of the Neandertal Genome by Array-Based Sequence Capture Science, 328 (5979), 723-725 DOI: 10.1126/science.1188046Eswaran, V. (2002). A Diffusion Wave out of Africa: The Mechanism of the Modern Human Revolution? Current Anthropology, 43 (5), 749-774 DOI: 10.1086/342639ESWARAN, V., HARPENDING, H., & ROGERS, A. (2005). Genomics refutes an exclusively African origin of humans Journal of Human Evolution, 49 (1), 1-18 DOI: 10.1016/j.jhevol.2005.02.006Green, R., Krause, J., Briggs, A., Maricic, T., Stenzel, U., Kircher, M., Patterson, N., Li, H., Zhai, W., Fritz, M., Hansen, N., Durand, E., Malaspinas, A., Jensen, J., Marques-Bonet, T., Alkan, C., Prufer, K., Meyer, M., Burbano, H., Good, J., Schultz, R., Aximu-Petri, A., Butthof, A., Hober, B., Hoffner, B., Siegemund, M., Weihmann, A., Nusbaum, C., Lander, E., Russ, C., Novod, N., Affourtit, J., Egholm, M., Verna, C., Rudan, P., Brajkovic, D., Kucan, Z., Gusic, I., Doronichev, V., Golovanova, L., Lalueza-Fox, C., de la Rasilla, M., Fortea, J., Rosas, A., Schmitz, R., Johnson, P., Eichler, E., Falush, D., Birney, E., Mullikin, J., Slatkin, M., Nielsen, R., Kelso, J., Lachmann, M., Reich, D., & Paabo, S. (2010). A Draft Sequence of the Neandertal Genome Science, 328 (5979), 710-722 DOI: 10.1126/science.1188021
