The expanding crest of modern humanity

By Razib Khan | July 20, 2012 12:46 am

If you are interested in genomics and human evolution, a new review paper in PLoS Genetics is a must read, Genomic Data Reveal a Complex Making of Humans. A must read not because you need to agree with the thrust of the authors’ arguments, but because it provides a thorough bibliography for the last 2 to 3 years. Here is the abstract:

In the last few years, two paradigms underlying human evolution have crumbled. Modern humans have not totally replaced previous hominins without any admixture, and the expected signatures of adaptations to new environments are surprisingly lacking at the genomic level. Here we review current evidence about archaic admixture and lack of strong selective sweeps in humans. We underline the need to properly model differential admixture in various populations to correctly reconstruct past demography. We also stress the importance of taking into account the spatial dimension of human evolution, which proceeded by a series of range expansions that could have promoted both the introgression of archaic genes and background selection.

The main problem I have at this point is the general mode of range expansions, whereby population A expands as a demographic wave across a substrate of population B. These sorts of models seem to assume a sort of continuous dynamic process. In contrast, I am beginning to suspect that much of the human demographic past was characterized by discrete events. The closer to the present the more I’m convinced of this, though honestly I am now pushing back my own timing for the origins of many of the human distinctive traits, such as culture, well before behaviorally modern humans.

MORE ABOUT: Human Evolution

Comments (7)

  1. Paul Jones

    Discrete events: Toba volcano, flooding of the Black Sea, closing of land bridges by rising waters, invasions?

  2. gcochran

    A range expansion is the natural default model, since A. it’s mathematically tractable and B. No one has ever seen anything very similar happen in human history.

  3. #2, how or why is B true?

  4. Tom Bri

    Well worth the time it took to read, and accessible to the informed layman.
    # 2, I am with # 3 on this. Was this sarcasm, or is there some point that I am not catching?

  5. #4, i think greg’s point is that normal demographic processes aren’t subject to a range expansion which is like a diffusion process. e.g., the american settlers did not range expand and dilute through the space of native american territory.

  6. FWIW, there is increasing evidence for something similar in language evolution. Models that show outsized levels of linguistic differentiation of the moment of language split are showing support both from statistical patterns of linguistic differences between related languages whose histories are known, and from psych lab studies that show advantages for language differentiation for those involved.

  7. Jess Tauber

    What I find interesting is that having studied phonosemantics over three decades and having looked at many different language families, there seems to be some sort of rough correlation between hybridization events recently discerned from genetic studies and the presence of large-scale systems within languages of highly transparent (pre)lexical items (ideophones). Since in their prototypical state ideophones (like onomatopoeia on steroids, but covering many more semantic domains than just sound) are prelexical (just as closed-class grammatical forms are post-lexical), this raises the question as to whether any genetic/neurological structures responsible for the implicational developmental hierarchical system of historical language processes were in some manner reset by such hybridization events, with aftereffect echoes even today in populations that underwent them.


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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


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