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Tuesday, July 19, 2011

Female hominids were the nomads

In many species, either females or males tend to live their whole lives in one area while the other sex disperses soon after reaching maturity.  This ensures that genetic diversity is maintained (though of course, the animals aren’t thinking about that).  Research on strontium levels in hominid teeth, led by Sandi Copeland of the University of Colorado-Boulder and the Max Plank Institute, suggests that for early hominids, it was the females who left home.

Specific strontium isotope ratios are associated with different types of soils. Those soil isotopes are absorbed by the local plants, and then by the local animals.  While some parts of the body are constantly being recycled, tooth formation ends when the tooth is enclosed by enamel.  Thus, the strontium isotopes found in an adult molar indicate where that person spent the first eight or so years of life.

The researchers examined 19 teeth from two million year old Australopithecus africanus and Paranthropus robustus individuals for isotopic strontium ratios.  The teeth were found in two cave systems located in a region with a distinct strontium ratio.  While the larger teeth (presumably from males) displayed that same local ratio, many of the smaller teeth did not.  If the authors are correct in assuming that small adult molars belong to females, this strongly suggests that the females had entered the cave systems after childhood.

You can watch an explanation by Copeland below: