The Hand Bone's Connected to the Wrist Bone...	March 24, 2000
by Angela M.H. Schuster

Comparison of the wrist end of the radius (forearm bone) of a chimpanzee, human, and two of our early human relatives (australopithecines); arrows indicate buttressing feature. (D. Strait/George Washington University)

Some of our earliest-known ancestors may have evolved from primates who walked on their knuckles rather than climbed trees according to a new report by George Washington University researchers Brian Richmond and David Strait. Comparing fossilized wrist joints belonging to 3.3-million-year-old Australopithecus afarensis (Lucy) and 4.1-million-year-old A. anamensis with those of other primates, Richmond and Strait noticed that even though these two species walked upright, a hallmark that sets hominids apart from other primates, their wrist structures resembled those of knuckle-walking, ground-dwelling primates such as chimpanzees and gorillas.

Buttressing features in Chimpanzees and gorillas wrist joinst that help lock their wrists in a stable position that can support a good portion of their weight on their fingers. These primates have relatively long fingers that allow them to grasp branches and climb trees, but when they walk on the ground, they protect their fingers by curling them and walking on the backs of their knuckles. The presence of the same wrist-locking mechanism in the early australopithecines suggests that their ancestors were knuckle-walkers. The trait disappears in later hominids, however, being absent in 2.0 to 3.0-million-year-old A. africanus, which possessed more humanlike, flexible wrist joints.

"For more than a century, scientists have hypothesized about how and why the first human ancestors began walking upright, but until now there has been very little evidence to help answer this question," said Richmond. "Our study demonstrates that our earliest ancestors did not simply come down from the trees. Rather, they evolved from an ape already adapted to life on the ground."

By showing that upright walking evolved from an ancestor that was already adapted to life on the ground, the study has major implications for theories on early human adaptation. "The belief that our ancestors began walking upright because they were forced out of trees by shrinking forests no longer holds true," says Strait. "It's more likely that they began walking upright when their hands were needed for other tasks like carrying food or making tools." Richmond and Strait published their findings in the March 23 edition of Nature.

© 2000 by the Archaeological Institute of America www.archaeology.org/online/news/knuckles.html

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