By Alan Bavley
KANSAS CITY, Mo. - Our celebrated ancestor Lucy was no waddling, hunched-over ape-woman who felt more at home in the trees.
New research from the University of Missouri in Columbia offers the most conclusive evidence yet that Lucy and her tribe spent their lives on solid ground and walked much as modern humans do - more than 3 million years ago.
Lucy, just 3 1/2 feet tall, would have been more capable of strutting her stuff on a dance floor than of swinging from branch to branch.
"I bet she could dance," said MU anatomy professor Carol Ward. "I don't know if I could do any better."
In research to be published Friday in the journal Science, Ward and two colleagues used a newly discovered foot bone from a dig in Ethiopia to determine that members of Lucy's species, Australopithecus afarensis, had arched feet like ours.
That may seem like a small detail, but it has huge implications for the course of human evolution.
And it may help settle a decades-old argument among scientists over whether Lucy was a dedicated land rover or still spent much of her time in trees, as many apes do.
Arches put a spring in her step and made it possible to comfortably stand and walk. But arches also took away the flexibility that lets apes grasp with their feet as they scramble up trees.
"Is she a shuffling ape that just stood up?" Ward said. "This tells us she's given up the ability to be good in trees to be good on the ground. There was no more compromise.
"We can walk well over distances, and that started with Australopithecus. It turned out to be a good plan for us."
The possibility that our early ancestors stood upright and walked with humanlike agility might surprise a lot of people, said Jeremy DeSilva, an anthropologist at Boston University.
Classic charts of human evolution often show a series of pictures of hulking chimplike creatures that gradually become more upright.
"The anatomical evidence just doesn't support that view," DeSilva said. "These (Australopithecus afarensis) were good upright walkers."
That suggests upright walking was favored early in human evolution, long before brains grew larger, DeSilva said. Lucy's brain wasn't much bigger than that of a chimpanzee.
But why did our ancestors leave the safety of the trees for life on the ground?
One possibility may have been climate change, said Bruce Latimer, a paleoanthropologist at Case Western Reserve University. Millions of years ago, huge forests that provided habitat for dozens of species of apes in Europe, Asia and Africa began to shrink.
But life on the ground held dangers for a two-legged animal.
"We're incredibly slow on two limbs," Latimer said. "If we injure one leg, that makes us leopard food. It's such a peculiar way to get around."
The big advantage of standing upright may have been that it freed the hands of Australopithecus to carry things, Latimer said.
A social system may have developed where males gathered food for their mates and offspring. That gave females the opportunity to raise more children.
"In evolution, the most important thing is having babies," Latimer said.
A decade ago, Latimer visited a site on the edge of the Serengeti plain in Africa where fossilized footprints of three of Lucy's species were discovered.
They show a small "Lucy" leading two larger ones single file over ash from a volcano that had recently erupted. The leader stopped and looked around. The two others stopped as well. Then the three began walking again.
"They could be mistaken for human footprints, except that they were 3.5 million years old," Latimer said.
Based on his own research, Latimer has long advocated that Lucy had an arched foot, but he never had enough evidence to prove it.
The fossilized bone, the fourth metatarsal, that Ward analyzed was the key to determining the structure of Lucy's foot, according to Latimer.
The fossil was found recently by William Kimbel of Arizona State University. The third researcher on the arch study, Donald Johanson, led the team that discovered the original Lucy skeleton in 1974.
The well-preserved metatarsal is one of the bones that connect the toes to the base of the foot. The way it is shaped shows that it's part of an arched foot. It matches its human counterpart very closely.
"It confirms a lot of what we were thinking but couldn't tell for sure," Latimer said.
(c) 2011, The Kansas City Star.