Monday, June 18, 2007

Skepticism About "Out-of-Africa"

Alan R. Templeton has long been a critic of those who would over-interpret the genetic data on human origins. He's not alone. There are a surprisingly large number of biologists who refuse to jump on the "Out-of-Africa" bandwagon. This group does not get the same amount of publicity as the advocates of a recent (<100,000 years) wave of migration out of Africa. I think it's because skepticism of a new theory is seen as sour grapes. That, plus the fact that it's hard to publish criticisms of work that's already in the scientific literature.

An upcoming issue of the journal Evolution will contain a review by Templeton on human origins and the Out-of-Africa theory. Right now it's only available online [GENETICS AND RECENT HUMAN EVOLUTION]. Here's the abstract,
Starting with "mitochondrial Eve" in 1987, genetics has played an increasingly important role in studies of the last two million years of human evolution. It initially appeared that genetic data resolved the basic models of recent human evolution in favor of the "out-of-Africa replacement" hypothesis in which anatomically modern humans evolved in Africa about 150,000 years ago, started to spread throughout the world about 100,000 years ago, and subsequently drove to complete genetic extinction (replacement) all other human populations in Eurasia. Unfortunately, many of the genetic studies on recent human evolution have suffered from scientific flaws, including misrepresenting the models of recent human evolution, focusing upon hypothesis compatibility rather than hypothesis testing, committing the ecological fallacy, and failing to consider a broader array of alternative hypotheses. Once these flaws are corrected, there is actually little genetic support for the out-of-Africa replacement hypothesis. Indeed, when genetic data are used in a hypothesis-testing framework, the out-of-Africa replacement hypothesis is strongly rejected. The model of recent human evolution that emerges from a statistical hypothesis-testing framework does not correspond to any of the traditional models of human evolution, but it is compatible with fossil and archaeological data. These studies also reveal that any one gene or DNA region captures only a small part of human evolutionary history, so multilocus studies are essential. As more and more loci became available, genetics will undoubtedly offer additional insights and resolutions of human evolution.

[Hat Tip: Gene Expression]


  1. The full paper is subscribers-only. Damnation.

    Intuition tells me that Templeton is on to something. I want to see his detailed claims. I've long thought there was something that didn't quite click about both the regional and Out-of-Africa hypotheses. The available fossil data simply doesn't match either one. In particular, they both founder on the data from Southeast Asia and Australia. I want to see if his interpretation does any better.

  2. I'm one of the non-experts and I want to try to get this right. The question is not about out-of-africa per se but about a more recent replacement hypothesis? Is that right? As a high school science teacher, this is another excellent example of interesting high school biology level theories that get discussed BUT we often only hear the mainstream newspaper version. We don't often hear the weighting of evidence and alternate hypothesis. Thank you Sandwalk and ScienceBlogs!
    So I suspect that the evidence fails to [strongly] support the hypothesis that modern Homo sapiens evolved within Africa and acted to replace earlier migrations that had occurred by other hominids? Do I have this right? Let me know please.

  3. Linzel,

    I certainly don't understand the nuances here (interested layman), but another seemingly balanced critique of out-of-africa is the (paleo)anthropologist John Hawks.

    IIRC he has an extensive discussion on this in the context of neandertals. (If not else, he taught me why it is the preferred spelling. :-)

    But here he outlines for his students how to differentiate the Multiregional evolution hypothesis from the Out of Africa hypothesis.

    And here is a post on Gene Expression discussing Templeton's previous work and Carl Zimmer's and John Hawks' analysis. "The point in challenging the Out-of-Africa only hypothesis is not to revive classical anangenetic Multiregionalism, that story is just as simplistic as Out-of-Africa only." Which I believe is Hawks' view as well.

  4. A fairly recent paleontological criticism of Out of Africa is:

  5. I recall the work of Dr. Spencer Wells and his book The Journey of Man, in which he did genetic testing of the Y-chromosome. He determined that all humans share a common ancestor. Is Templeton refuting this claim?

  6. For us non-subscribers, can you briefly summarize Templeton's "model of recent human evolution that emerges from a statistical hypothesis-testing framework"? Thanks.

  7. I have recently been watching BBC's "Incredible Human Journey" presented by Dr Alice Roberts. I don't have a scientific background, but to me the whole thing seems rather 'Disneyesque'. Dr. Alice is cute and the presentation is good, but the hypotheses would seem weak. Incidently, perhaps this is not a scientific concern, but it seems in the program's efforts to make people feel proud of being African, it actually comes across as a bit demeaning of Africans. I can see 19th Century eugenics rearing it's ugly head again.