Apr. 3, 1998 She wasn't faster than a speeding bullet, but new research seems to indicate that Lucy and other early known human ancestors walked with greater ease and efficiency than previously believed, despite their short legs.
Conventional thought among paleoanthropologists has been that the short-legged australopithecines, such as Lucy, were primitive or ape-like and hominids developed long legs because they are characteristic of efficient bipeds. Not so, says Patricia Kramer, a University of Washington doctoral candidate and lecturer in anthropology, who will present evidence Thursday morning at the annual meeting of the American Association of Physical Anthropology in Salt Lake City that "Lucy was beautifully equipped to deal with her world" 3.2 million years ago.
Lucy is the name given to the skeleton of a small female Australopithecus afarensis found by Donald Johanson in Ethiopia in 1974. The skeleton is about 40 percent complete, which is unusually rare among early human ancestors. Many species, including other australopithecines, are only represented by scant fossil remains.
Kramer, who is a registered civil engineer and worked at Boeing as a structural engineer, took a distinctly unconventional approach toward her research, which is the basis of her doctoral dissertation. She used standardized equations that can, for example, calculate if the cargo doors on an airliner close properly, fit into place correctly and won t break. But instead of solving engineering problems, she used them to explain the evolutionary record of early humans.
"The equations can predict how much energy is required for something to move in space," explains Kramer. "If you take them and develop models that take into account the different leg lengths for Lucy and modern humans and calculate the different levels of energy required for each, the result is a comparison of how much energy is required for Lucy and a modern human to move at any speed."
Kramer worked three speeds -- slow, normal and fast -- into her program. Slow corresponds to a person out on a leisurely stroll. Normal is equal to the speed an average urban American would use while not in a hurry but having some place to go. Fast is "pushing the envelope of running but still walking, such as a woman who is late for a meeting and rushing in high heels," says Kramer. In her model, she compared the three-foot-tall Lucy, who weighed about 70 pounds and had a stride that covered a little more than three feet, with a modern 5-foot 6-inch American or European female weighing 120 pounds whose stride is about four and a half feet.
Using her model, Kramer determined that Lucy and her brethren walked through life at a speed we would call a stroll.
"Lucy was a slow-speed forager and walked from one patch of trees to another. Her environment was plentiful enough that there was no demand for her to walk fast or go very far. So her day-range was pretty small, but it allowed her to get enough to eat and be very efficient at walking," says Kramer.
That walking speed matched the environmental demands of the time and allowed australopithecines to conserve energy that they needed to build and maintain their bodies and to reproduce, she explains.
"This is particularly important in primate females because of the incredible demands in raising offspring," says Kramer. "Being a mother requires a great deal of energy. If animals can gather the necessities of life efficiently, they have more energy to devote to their offspring or to have more offspring. Natural selection should favor those who walk efficiently by allowing them to have either healthier babies or more of them," says Kramer.
The fossil record shows australopithecines lived for nearly 3 million years. Eventually, however, they died out and were replaced by long-legged Homo habilis and Homo erectus, who first appeared about 2 million years ago.
"Something happened," says Kramer. "Probably the environment changed and food became less abundant. So it became necessary for Lucy's descendants to have a larger day range. Basically leg length increases as animals need to go faster or farther. There is evidence that from 2.8 million to 1 million years ago the climate got progressively drier and vegetation became more and more sparse. So maybe what happened was the australopithecines couldn't get enough food and they died out."
Gerald Eck, a University of Washington paleoanthropologist who participated in several expeditions with Johanson in Ethiopia, says Kramer's research "adds a fundamental piece to our understanding of the differences between adaptations of Australopithecus and Homo. And she does this using a new method for paleoanthro- pology. But I fear that because most paleoanthropologists, like myself, are neither mathematicians nor engineers they will find her method difficult to follow and thus her conclusions won't receive the recognition they deserve."
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