Puzzling over pre-humans

Posted: Monday, October 06, 2008 9:43 AM by Alan Boyle

Dave Einsel / Getty Images file A sculptor's rendering, part of an exhibit focusing on the 3.2-million- year-old hominid called Lucy, shows how she might have looked in life.

The world’s best-known skeleton of a human ancestor - whose name, "Lucy," came from a Beatles song - now lies splayed out in Seattle's Pacific Science Center like ornaments in a glass jewelry case. Or, more aptly, like 3.2-million-year-old pieces of a jigsaw puzzle.

Anthropologists are still working on the puzzles about human origins that have been posed by Lucy and other fossils, including a major find that was made just a couple of miles away from the place where Lucy was found 34 years ago.

The long-running mystery surrounding the "First Family" - a grouping of fossil bones representing up to 17 of Lucy's kin from Ethiopia's Afar region - is just one of the many unresolved plot threads in the scientific story about our long-ago ancestors.

"Lucy's Legacy," an exhibition that began its Seattle run last weekend, recaps the story so far. The traveling exhibit made news last year when it came to the Houston Museum of Natural History, because it represented the first time the Ethiopian government allowed Lucy's skeleton to be displayed abroad. Since then, the cultural controversy has settled down - but scientific controversies continue.

Almost human?
Lucy and the rest of her species (named Australopithecus afarensis, Latin for "southern ape of Afar") were not human, in everyday terms or technical terms. They looked more like apes than humans, and stood only about three and a half feet (1 meter) tall. But the point is that they stood at all: An analysis of Lucy's pelvis and leg bones indicated that she was capable of walking upright, making her the earliest known specimen exhibiting solid evidence for that trait.

© Pacific Science Center

The skeleton of a 3.2-million-year-old hominid named Lucy is displayed at the "Lucy's Legacy" exhibit at Seattle's Pacific Science Center.

Other bones revealed a blend of simian and human features. As I stared down at the jewel case, on display at the Pacific Science Center's "Lucy's Legacy" exhibit, I was most struck by Lucy's V-shaped jaw, lined with fossilized teeth. That, more than anything, gave me a sense of how small and strange-featured Lucy must have been.

For Donald Johanson, the Arizona State University paleoanthropologist who was one of Lucy's discoverers, the jaw told much more: The shape of the bone, the alignment of the teeth and even details about the cusps of Lucy's premolars all told him that Australopithecus afarensis was more apelike than humanlike from the neck up.

The implication was that Lucy's upright walking came before the bigger brains of her descendants. Today, the mainstream view is that australopithecines like Lucy first became bipedal - perhaps as part of an adaptation to living on Africa's savannahs instead of ape-friendly forests. That evolutionary development opened the way for more dextrous hands, and then brains more suited for manipulating tools.

Upright walking has thus come to be considered the key dividing line between the evolutionary branch leading to humans (a category of creatures known as hominids) and the other branches leading to today's non-human primates.

Even assuming that's the right story to tell, there are plenty of gaps in the narrative: Does Lucy really represent the single branch leading to humans, as Johanson proposed? Or is the lower part of the human family tree more like a tangle of shoots and roots, with bipedalism and other humanish traits emerging on multiple fronts? Exactly what kinds of evolutionary pressures were at work? How much did hominids have to cope with natural predators and ancient climate change?

These questions are being pursued by researchers spread out across Africa, from Ethiopia down to South Africa and northwest to Chad. Several years ago, the discovery of a 6- to 7-million-year-old skull in Chad sparked a debate over whether upright walking went much farther back in the family tree, and that debate is still not entirely resolved.

3 million-year-old cold case
Some of the biggest questions surround the First Family, the fossils found by Johanson and his colleagues a year after Lucy's discovery. The collection of more than 200 bones came from the same time frame in which Lucy lived, from the same place, and apparently from the same species. Thirteen to 17 individuals are represented, ranging from juveniles to adults.

To anthropologists investigating the First Family's demise, the mystery is, if anything, even juicier than Lucy's saga.

"It's very much like a forensic case, where you've got an unexplained death ... and you're trying to figure out what happened, only this case is 3 million years old," said the Smithsonian Institution's Anna Kay Behrensmeyer, who has been studying the case for years.

Even Johanson has said the First Family is as deserving of fame as Lucy. According to South African reports, he's trying to nail down the evidence for the cause of death by consulting with an expert on prehistoric predators.

In the past, investigators have suggested that the entire troop of hominids might have died in a flash flood, or were done in by a bout of food poisoning. But Behrensmeyer said the current prevailing theory is that they were the victims of a "surplus killing" by blood-crazed predators. "This is documented as a natural phenomenon," she said.

Behrensmeyer noted that the biggest predators of the time were saber-toothed cats. One scenario suggests that the cats massacred a whole troop of hominids, perhaps leaving behind remains to be scavenged by the ancestors of modern-day hyenas.

But anthropologists are still only in the early stages of the investigation. Some still question whether the First Family was actually a familial unit, or instead represented a variety of hominid species whose bones were cached together by scavengers. Additional pieces of evidence could produce dramatic plot twists, just as they do in the TV crime dramas.

"It's important to get the facts straight," Behrensmeyer said. "What's critical about this is, first of all, to determine whether all these specimens were buried together."

The time frame was far too early for the type of intentional burials that early humans and even Neanderthals were capable of performing, she said. Nevertheless, unraveling the case of the First Family will add a new chapter to the story of Lucy and our other long-ago ancestors.

"It does say a lot about how they died, and how they lived," Behrensmeyer said.

More resources
For much more about the Lucy exhibit, check out the "Lucy's Legacy" Web sites for Houston and Seattle, as well as coverage from the Seattle Post-Intelligencer. "Becoming Human" and the Institute of Human Origins' Web site delve into paleoarchaeology in general and Johanson's work in particular. You can also check out the Smithsonian's Human Origins Program and the Leakey Foundation. Our own special report on evolution, "Fast Forward," features an interactive graphic on human origins as well as potential human futures.

If you're looking for books about human origins, you can sink your teeth into one or all of these three, which serve as this month's triple selection for the Cosmic Log Used Book Club.

• "Lucy: The Beginnings of Humankind," by Donald Johanson and Maitland Edey.
• "The First Human: The Race to Discover Our Earliest Ancestors," by Ann Gibbons.
• "Before the Dawn: Recovering the Lost History of Our Ancestors," by Nicholas Wade.

The CLUB Club highlights books with cosmic themes that you should be able to find at your local library or secondhand-book shop.

Update for 2:15 p.m. ET: A sharp-eyed commenter recalled that Lucy's bones were brought to the Cleveland Museum of Natural History after their discovery. At the time, Johanson was a curator at the museum, and he worked out a deal with the Ethiopian government to bring Lucy to Cleveland for study in 1975. The bones were returned to Ethiopia in 1980, without going on public display. I've revised this item to make allowance for Lucy's scientific sojourn.

EMAIL THIS