All living humans are interfertile – one species by definition.  People from all parts of the globe can marry and have children, even though global travel is relatively recent in human history.  Yet we know there is considerable variability between tribes and nationalities.  Does this variability take millions of years?  Does it lead to the origin of new human species?  Recent evidence shows that variations can be rapid, both genetic and acquired, without reducing interfertility.

Jawboning about wisdom teeth:  A new study is something to chew on: diet, not evolution, may influenced human jawbone shape.  Nature (1 Dec 2011) mentioned a paper in PNAS (http://dx.doi.org/10.1073/pnas.1113050108) about how jaw shape appears to be systematically different between hunter-gatherers and agriculturalists.  Hunters have bigger jaws with more room for teeth, apparently due to the exercise of chewing.  According to the abstract, the finding explains “why there is often a mismatch between the size of the lower face and the dentition, which, in turn, leads to increased prevalence of dental crowding and malocclusions in modern postindustrial populations.”  Nature commented, using evolutionary dating assumptions, that “Agriculture and animal farming began emerging around 10,000 years ago in various regions of the world. As populations turned to farming, a diet of softer, more processed foods may have spurred the evolution of daintier jaws.”  It’s not really evolution, though, if there has not been the origin of a new species – it’s just variation.  Or, it might be an acquired characteristic.  Experiment: feed your youngster mammoth meat for 20 years, and see if he or she stays free of wisdom tooth problems.

Rapid head shape evolution:  The Xavánte Indians of Brazil have a characteristic head shape that differs from neighboring tribes.  The conclusion of a paper in PNAS (http://doi: 10.1073/pnas.1118967109) is that cultural traditions led to the “evolution” of this trait.  Live Science said, “Culture may trigger rapid evolution of various human features, suggests new research into the marital practices of a tribe from the Brazilian rainforest.”  Once again, though, this is not evolution, since the Indians are still Homo sapiens.  The abstract indicates that the authors were startled by their own conclusions, which logically could be extended to all “racial” differences around the world:

We found that the Xavánte experienced a remarkable pace of evolution: therate of morphological change is far greater than expected for its time of split from their sister group, the Kayapó, which occurred around 1,500 y ago. We also suggest that this rapid differentiation was possible because of strong social-organization differences. Our results demonstrate how human groups deriving from a recent common ancestor can experience variable paces of phenotypic divergence, probably as a response to different cultural or social determinants….

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