If Ardi’s skeleton was an unexpected mosaic, her habitat was even more curious. The Middle Awash scientists analyzed more than 150,000 vertebrate fossils from the site, from rats to foxes to saber-toothed cats, along with hundreds of geologic samples, to arrive at a detailed understanding of Ardi’s habitat. “It was like a whole series of snapshots across an ancient landscape,” White says.
For decades anthropologists have argued the “savanna hypothesis”: that bipedalism evolved on the savannas of Africa as spreading grasslands forced our ancestors to walk increasing distances across open territory. As White and his team analyzed their evidence, they realized that Ardi must have lived in the woods. In that case, bipedalism must have emerged for different reasons. “Since her species was already bipedal and already had reduced canines, those characteristics were not the result of adaptation to savanna,” White says.
But Ardi’s most important legacy could be the light she sheds on our last common ancestor, that mysterious creature that ultimately gave rise to both today’s humans and our closest living relatives, the chimpanzees. “There’s a big gap in our knowledge about our past,” White says, “and it lies down there somewhere about 7 million years ago in the form of a last common ancestor. It may never be found. But Ardi tells us what that creature looked like, and it’s something we never expected.”
The long-favored view is that the last common ancestor must have been similar to a chimp, with more evolutionary change occurring subsequently on the human branch of the family. But Ardi’s anatomy suggests that our last common ancestor was like neither a human nor a chimpanzee. The shape of Ardi’s hands makes the point. Their anatomy contains bony structures that would have allowed her to walk comfortably on her palms, more like monkeys than like living apes. “The Ardi wrist is wholly unlike a modern ape wrist,” Lovejoy says. “Apes can’t bend their wrist backward, and it’s the bending of the wrist backward that allowed Ardi to walk on the palms.” In contrast, modern apes like gorillas, chimpanzees, and bonobos walk on their knuckles, an adaptation that was always assumed to be ancient.
Not everyone likes these surprises. “People are tightly invested in the chimp as a model for our ancestors,” White says. “The idea that the chimpanzee is basically a living missing link is deeply embedded in paleoanthropology. Ardi is not particularly chimpanzee-like, and we’ve gotten a lot of extreme pushback on that.”
University of Toronto paleoanthropologist David Begun is one of the skeptics. “Ardi lived at least 2½ or 3 million years after the split of chimps and humans,” Begun says. “The idea that this fossil tells us what the last common ancestor looks like is unfounded. Ardi is a spectacular discovery, but it may actually be an early side branch of hominids that is not even directly related to Lucy or humans. It’s naive to think every fossil you find is directly on the line leading to humans. And if we evolved from a monkeylike quadruped,” as Lovejoy’s analysis of Ardi’s hands suggests, “then all our extensive anatomy related to suspension and hanging would have evolved in parallel to the great apes. That’s possible but unlikely.”
Others question whether Ardi was truly a biped. William Jungers, the Stony Brook paleoanthropologist, and a group of colleagues spent several days in White’s lab last year. After examining the casts and digital images, Jungers decided that “Ardi was at best a facultative biped,” a creature that is capable of walking but somewhat inefficiently. That description also fits modern chimps, gibbons, and even capuchin monkeys. Jungers also questions the idea that male food-gathering turned A. ramidus into upright walkers. “Owen’s provisioning theory is untestable,” he says. “Striding bipedalism is obviously a dandy adaptation, but there is no shortage of colorful and plausible speculations as to why it occurred, from thermoregulation to sexual displays, from looking over tall grasses to wading through the water.”
Even the savanna hypothesis is not dead yet. Geochemist Thure Cerling of the University of Utah and seven other geologists and anthropologists recently questioned the ecological reconstruction from White’s team. Cerling reexamined the soil and tooth enamel data provided by White and concluded instead that Ardi lived in a bush-savanna, with less than a quarter of the area providing canopy cover. “I believe their data indicate a significant savanna influence,” Cerling says. White heatedly disagrees. The point is that Ardi’s particular habitat was woodland, he says, even if savanna was nearby.
Ardi has been hit with one potshot after another since she was unveiled to the world. Tim White’s answer to all the objections? “Some people have a hard time wrapping their minds around the anatomical mosaic that Ardi represents and its implications for human origins,” he says. “You’re able, as you take those sand grains away from the fossil, to see a creature that nobody has seen for the last four and a half million years.”
Flo, the Hobbit Person
“Big” has been the sine qua non of our success as humans. Relative to our ancestors and most of our primate cousins, we have large bodies, long limbs, and oversize brains. It seemed that only in our bigness could we stride out of Africa and across the planet. But maybe bigness was unnecessary. That is the message from a strange Indonesian fossil belonging to a previously unknown species of the human family: Homo floresiensis, the hobbit people. If Ardipithecus has utterly upset our notions about early human origins, the hobbits have altered our thinking about late human evolution by showing us, among other things, that small might be just as adept.
The ancestors of hobbits probably left the rift area of Africa (Ardi’s home) for Southeast Asia on foot about 2 million years ago, ultimately crossing treacherous ocean waters to land on the narrow, 230-mile-long Indonesian island of Flores. More amazing, hobbits seem to have survived into modern times alongside modern humans; they fashioned stone tools, hunted cooperatively, and even cooked with fire—all with a brain just one-third the size of that of a typical Homo sapiens adult.
The key hobbit skeleton is an adult female named LB1 for the place where it was found: a vast, open, sun-drenched limestone cave called Liang Bua, on Flores. In the tradition of giving notable hominid fossils familiar names, LB1 was nicknamed Flo. In addition to Flo, archaeologist Michael Morwood of the University of Wollongong in Australia found partial remains of as many as 14 other individuals in the same cave, all of them presented to the world in the journal Nature in 2004.
After the publication of Morwood’s article, the hobbit immediately became a scientific and media sensation. Flo is “one of the most complete fossils found anywhere until you get to true burials, like in Neanderthals and early modern humans,” says Jungers, who has been closely involved in Homo floresiensis research.
Flo and her species lived on Flores from about 90,000 years ago until about 14,000 years ago, when they were wiped out—perhaps by a volcanic eruption, or perhaps by competition with modern humans. If they did interact with humans, the hobbits may have inspired the local legends of a small, hairy, humanlike creature that some Flores natives call the Ebu Gogo (which loosely translates to the “grandparent who eats anything”), anthropologist Gregory Forth of the University of Alberta speculates.