Out of who knows where

By Razib Khan | January 30, 2012 10:21 pm

In The New York Times, DNA Turning Human Story Into a Tell-All:

The tip of a girl’s 40,000-year-old pinky finger found in a cold Siberian cave, paired with faster and cheaper genetic sequencing technology, is helping scientists draw a surprisingly complex new picture of human origins.

The new view is fast supplanting the traditional idea that modern humans triumphantly marched out of Africa about 50,000 years ago, replacing all other types that had gone before.

Instead, the genetic analysis shows, modern humans encountered and bred with at least two groups of ancient humans in relatively recent times: the Neanderthals, who lived in Europe and Asia, dying out roughly 30,000 years ago, and a mysterious group known as the Denisovans, who lived in Asia and most likely vanished around the same time.

Their DNA lives on in us even though they are extinct. “In a sense, we are a hybrid species,” Chris Stringer, a paleoanthropologist who is the research leader in human origins at the Natural History Museum in London, said in an interview.

First, for reasons of novelty we are emphasizing the exotic tendrils of the human family tree. Even Chris Stringer, the modern paleontological father of “Out of Africa,” is claiming we’re hybrids! But let’s not forget that non-Africans are the product of a very rapid radiation out of the margins of the Afrotropic ecozone within the last ~50-100,000 years. I am not entirely sure that this is as true of Africans (recall how extremely basal Bushmen are to the rest of humanity; they seem to have diverge well before the “Out of Africa” pulse).

Second, the old model was way easier to write about, even if there were confusions like the idea that mtDNA Eve was our only female ancestor from 200,000 years ago in the past. The new paradigm leaves one with awkward and unhelpful turns of phrase. For example:

But Dr. Reich and his team have determined through the patterns of archaic DNA replications that a small number of half-Neanderthal, half-modern human hybrids walked the earth between 46,000 and 67,000 years ago, he said in an interview. The half-Denisovan, half-modern humans that contributed to our DNA were more recent.

How to make sense of this gibberish? I suspect that the author didn’t have a good idea how to translate a particular population genetic statistic, and its importance to assessing time since admixture, into plainer prose. I have no idea either!

In other news, i09 has an interesting interview up with Rebecca Cann and Mark Stoneking. These two were heavily involved in the mtDNA Eve controversies of the 1980s. Nice capstone to an era. Like Stringer, even they admit the likelihood of a necessity to modify the simple “Out of Africa” with replacement model.

MORE ABOUT: Admixture, denisovan

Comments (13)

  1. Kirby is still Kirby no matter what he absorbs.

  2. AG

    Evolution is complicated process of replacement and hybridization at the same time. Evolution should be considered as survival of the fittest genes instead of species. Genocide style evolution is always problematic.

  3. Doug1

    So the is the author of the piece, ALANNA MITCHELL, Nicholas Wade’s replacement at the NY Times?

    Anyone know why Wade left?

  4. observer

    Yeah, the paragraph on the half-modern half-other hybrids is a bit strange. My guess, though, is that’s it’s saying no more than that once upon a time modern humans and Neanderthals/Denisovans mated, were interfertile, producing these hybrids. And of course, these hybrids in turn mated with other modern humans or Neanderthals/Denisovans.

    But focusing on the particular step in which they are half and half seems just weird. I can’t imagine that there was anything like a separate tribe of half-modern half-other human beings — why on earth should there be? So what’s the significance of pulling out this step, other than to make the point that the two groups mated and produced offspring?

  5. #3, i think he’s writing a book, and accepted a buy out.

  6. Insightful

    Razib, in the interview with Rebecca Cann and Mark Stoneking that you linked, Rebecca makes a point you may or may not disagree with. She says:

    So now we know that from Neanderthals and Denisovans that some isolated bits of earlier human genomes have survived in some specific populations, but that is a tiny fraction, a REALLY tiny fraction, of the total diversity of human genes.

    They make it seem miniscule and the word “really” was capitalized in the article. This makes Neanderthal and Denisovan contribution seem negligible as if we were ‘splitting hairs’ so to speak.

  7. #6, no, i don’t agree. also, it is not surprising that this is rebecca cann. she seems more strident on this issue. stoneking endorses the ‘leaky replacement’ model.

  8. dave chamberlin

    Rebecca Cann goes on to say ” We are a new species, we went through a period where we were like an endangered species, a very isolated population. We came very close to going extinct.”

    Is this proven? It just seems highly unlikely to me that we would almost go extinct right when we were on the verge of modernity. Yes there is evidence of a population bottleneck but isn’t this bottleneck more likely because this small population had cognitive advantages and expanded rapidly.

  9. ackbark

    #5. He’s trying to say these were super-powered characters named Hercules and Zeus and so forth.

  10. Darkseid

    i don’t know what i’ll do without Wade there. he was my fav. NYT writer by far. is this new girl trustworthy?

  11. AndrewV

    @#6 I would hazard to assert that there are some exciting times ahead.

    I am not going to be surprised if it turns out that there is much more to the story than just Neanderthals and Denisovans.

    Archaic DNA data mining for dummies :

    The idea that there were some seriously promiscuous hominids in our past is firmly embedded in my mind at any rate.

  12. They’re gettin’ to the good stuff:

    “Pääbo says he may soon start gathering data on methylation of Neanderthal DNA as part of his work on Neanderthal genomics. Epigenetics is already thought to occur in humans – it has been cited as an explanation for the high incidence of post-traumatic stress disorder among those whose parents survived the holocaust. Epigenetic data spanning a much longer interval in human prehistory could reveal that the process was key to adapting quickly to a wide range of environmental conditions during the Pleistocene.”


  13. Darkseid

    that reminds me that i’d like to vote for a GNXP update post on the state of epigenetics. maybe something to clear the air about the issue because i think most people don’t realize we inherit our epigenome too…i think. everyone’s starting to use it to downplay heritability at their convenience.


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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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