Monday, June 6, 2011

Male Australopithecines Were Not House Husbands

Evolution research is routinely misreported in the Indian media and I had a chuckle when I read this summary published in the Times of India:

Early women worked, men stayed home:

Early species of cavemen who roamed the earth two million years ago did not go to work but stayed at home and looked after the kids, while their females earned bread for the family, says a new research.

Scientists at the University of Oxford arrived at the conclusion by using new techniques to extract information from the fossilized teeth of our ancient human ancestors.  the conclusion scientists reached after studying strontium isotope content of fossilized teeth from two species of ancient hominins from South Africa was not about the daily division of labor between the sexes but about another aspect of their social life.

Different rock types like granites, basalts, dolomites have characteristic strontium isotope signatures. Plants take up strontium from bedrock and derived soil. Animals eat those plants and the strontium ends up in the enamel of their teeth. Analyzing the strontium isotope values of ancient mineralized teeth can help identify the geological substrate on which ancient animals, in this case ancient hominins lived. 

Scientists tested 19 teeth from the Sterkfontein and Swartkrans cave sites in South Africa dating from about 2.4 to 1.7 million years ago from two hominin species, Australopithecus africanus and Paranthropus robustus. These samples were preserved in a dolomite substrate.

The fragmentary body fossil record of these two species hints at a considerable degree of sexual dimorphism i.e. the females were significantly smaller in size than the males. When the the teeth were analyzed scientists found that a large proportion of smaller teeth likely belonging to females show strontium isotope values not reflecting the local landscape i.e. not reflecting the dolomite substrate, suggesting that many females had come into this area from outside the geological terrain where these sampled populations lived. On the other hand,  a large proportion of teeth likely belonging to males reflected local geology.

So, the inferences drawn from the strontium isotope values were (a) in these ancient hominins, females on reaching maturity dispersed away from their natal or family group and joined another group while males remained with their group and did not migrate elsewhere, and (b) male hominins had small home ranges i.e. they stayed most of their lives in a relatively small area.

Many social animals show a pattern of either the females or males leaving their family group on maturity, a behavior that may have evolved to minimize inbreeding. The social pattern of female dispersal inferred in these ancient hominins is similar to that seen in chimpanzees and many modern human societies as well.

Social behavior does not fossilize. Tools made by ancient humans is one way to understand certain aspects of behavior. In this case the scientists linked a physiological mechanism - the uptake through food and localization of strontium in teeth - to social behavior.

I thought it is a smart piece of forensic science.. even though it didn't tell us whether or not those ancient males were house husbands!

Science Daily summary.


  1. To us zamaney mein bhi bahoo-ein apnaa ghar chhod ke sasuraal aatee thee :)

  2. a very ancient tradition indeed - :)