Friday, August 18, 2006

Reconstructing human origins in the genomic era   posted by the @ 8/18/2006 03:55:00 PM

You'll want to read this:

Daniel Garrigan and Michael F. Hammer "Reconstructing human origins in the genomic era" Nature Reviews Genetics 7, 669-680 (September 2006)


Analyses of recently acquired genomic sequence data are leading to important insights into the early evolution of anatomically modern humans, as well as into the more recent demographic processes that accompanied the global radiation of Homo sapiens. Some of the new results contradict early, but still influential, conclusions that were based on analyses of gene trees from mitochondrial DNA and Y-chromosome sequences. In this review, we discuss the different genetic and statistical methods that are available for studying human population history, and identify the most plausible models of human evolution that can accommodate the contrasting patterns observed at different loci throughout the genome.


  • Over the past two decades, phylogenetic analyses of mitochondrial DNA and Y-chromosome polymorphisms supported a simple model of human origins, called the single origin hypothesis.

  • The single origin model proposes that anatomically modern humans trace their ancestry to a single small population that lived in Africa, and that, following a speciation bottleneck, the population expanded and completely replaced archaic forms of humans.

  • More sophisticated methods of analysis, based on the coalescent approach, are being applied to a plethora of new genomic sequence data.

  • These new analyses of multilocus sequence data show a large variance in the shape and depth of genealogies for X-chromosomal and autosomal loci, and present a more complex picture of human demographic history.

  • Non-African populations have reduced diversity and fewer rare polymorphisms than African populations, suggesting a history of bottlenecks. By contrast, African populations do not exhibit the predicted patterns of polymorphism after a speciation bottleneck.

  • These genome-scale patterns could be best accounted for by models that involve low levels of gene flow among archaic populations before the emergence of anatomically modern humans - that is, they imply the existence of ancestral population structure.

  • There is also growing evidence that some highly divergent genetic lineages might have entered our genome through hybridization between an expanding anatomically modern human population and archaic forms of humans.

  • Further tests of the predictions of these models await more systematic surveys of DNA sequence variation in multiple human populations, along with more sophisticated methods of population genetic inference.