Dispute grows over 'mama's boys' prehistoric theory
— -- With the dawn of humanity 2.2 million years ago, it appears that our early ancestors just hung around the house like a pack of mama's boys. But were they?
Sure looked that way last year, when researchers reported on telltale teeth from two pre-human species found in South African caves.
"We were somewhat surprised at our major finding," said Max Planck Institute for Evolutionary Anthropology scientist Sandi Copeland, now a visiting professor at the University of Colorado-Denver and lead author of the study in the journal Nature. The big teeth, presumably belonging to males, pointed to early male "hominins," our pre-human ancestors, hanging around their home caves most of their lives, while about half of the female ones appeared to be immigrants from elsewhere.
Outside researchers were more than somewhat surprised. One of the pre-human species called Australopithecus africanus, is widely seen as a possible ancestor to people today, so their early behavior might point to something interesting about us. Maybe, deep down, there's a little homebody inside every dude or a bit of wanderlust in every gal.
Naturally, as happens so often in science, the criticisms of the finding are starting to roll in. "This finding is potentially very important, as it would constitute direct evidence that early hominins shared a dispersal pattern similar to that of both (chimps) and modern (people)," notes anthropologist J. Michael Plavcan of the University of Arkansas-Fayetteville, in an upcoming Journal of Human Evolution study. "Unfortunately," Plavcan says, a second look at the tooth data, "suggests that this inference is not clearly supported."
In the 2011 study, Copeland and her colleagues looked at traces of radioactive strontium in the teeth of the two species, with the other one being the more ape-like Paranthropus robustus, dated to a cave from about 1.8 million years ago. The strontium, tested from 19 individuals' teeth from both species, revealed the places where the creatures lived during childhood, when their adult teeth formed. If the strontium traces matched the cave where they were found, the creature was local and if not, they must have moved from somewhere else. What the researchers found was that 90% of the big teeth came from locals, whereas about 50% of the small ones didn't.
That isn't good enough to make claims about which teeth belonged to whom, Plavcan says. He complains that mixing teeth from two species is a bad idea, statistically speaking, and that the 2011 study team's estimate relies too heavily on measures taken from the pointy "canine" teeth rather than molars.Canines differ much less in size between men and women than other teeth, such as molars.
More criticism came last month when Nature released a study led by Vincent Balter of France's Ecole Normale Supe´rieure de Lyon that used radiation tests to look at more teeth from South African cave fossils. Comparison of teeth from the same species as in Copeland's study and from another pre-human one called Australopithecus sediba, about 2 million years old, suggests they had different eating patterns. Australopithecus africanusate a much wider variety of food, more woody plants and meat, making comparison of their teeth for statistical purposes in the 2011 study look like a shaky idea.
