In all the celebrations of the 200th anniversary of Charles Darwin’s birth and the 150th anniversary of the publication of On the Origin of Species, it’s easy to forget that when Darwin made his prediction in 1871 that the ancestor of humans arose in Africa, it was an educated guess—he had no evidence from the fossil record. It wasn’t until 1924, in fact, that he was proved correct. That’s when the first skull of a human ancestor was unearthed in Africa: the Taung child, now recognized as a member of Australopithecus africanus, which lived about 3 million to 2 million years ago.
Credit: D. Strait and G. Weber
But even though it was the first hominid recognized from Africa, and many more specimens have since come to light, questions linger about A. africanus, including whether it was our direct ancestor and what it ate. In a study published online this week in the Proceedings of the National Academy of Sciences early edition, researchers take a new look at the familiar face of this species and find that it had the anatomy to be an adept nutcracker.
Paleoanthropologist David Strait of the University at Albany in New York state and his colleagues found that A. africanus evolved jaws, teeth, and a face that would have been particularly good at withstanding large forces on its premolars—precisely the place where humans and other primates crack large objects, such as nuts that are too big to chew with our molars. (Most of us can’t open our mouths wide enough to crack a walnut on our molars comfortably.)
Strait thinks that A. africanus ate a wide variety of foods but could rely on nuts in dry seasons when the ripe fruit and other plants and animals it preferred were scarce. Those australopithecines who could eat more nuts in times of scarcity were more likely to survive and, thus, passed on genes for big molars and premolars (as well as bony columns to buttress their faces) to their offspring. This nutcracker jaw flies in the face of an older theory that A. africanus was a picky eater, specialized to eat small, hard objects, such as seeds and grit, a strategy that some suggested might have led to its extinction.
This study is the second in a year to suggest that the distinctive powerful jaws of some australopithecines may reflect what they ate part of the time, not all of the time (Science, 2 May 2008, p. 608). And that, says Strait, suggests that simplistic ideas about australopithecine diets, based on tooth and jaw size, and why they went extinct, need to be reevaluated.
—Ann Gibbons
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