Everything you do has a history. You wake up each morning and get out of bed using an anatomy that allowed your ancestors to stand upright at least 4 million years ago. You go to the kitchen and eat cereal with a bowl and spoon that are part of a toolmaking tradition at least 2.5 million years old. As you munch your cereal, you page through the newspaper, which you can understand thanks to a brain capable of language, abstract thought, and prodigious memory—a brain that has been expanding for 2 million years. Until a few decades ago, most of that evolutionary history was hidden from science's view. But these days hardly a month goes by without news of a significant discovery. Paleoanthropologists keep digging up new fossils of our ancestors, and some of those fossils have even yielded DNA fragments. Meanwhile, geneticists have compiled a veritable encyclopedia of evolution—the sequenced human genome—and within a few years they'll be able to compare it with the genome of one of our closest living relatives, the common chimpanzee. Still, what we don't know about our evolution vastly outweighs what we do know. Age-old questions defy a full accounting, and new discoveries introduce new questions. That's not unusual for any field of science, but the eight mysteries on the following pages are intimate ones, because understanding our origins is key to understanding ourselves.
WHO WAS THE FIRST HOMINID?
Time travel would make everything so much easier. imagine that you could drop down by an African lake some 7 million years ago and watch the parade of aardvarks, antelopes, and elephants pass by until, sooner or later, you caught sight of a group of apes. They'd probably look something like chimpanzees—about the same height, with the same coat of hair—but their flat faces and the other odd proportions of their bodies would indicate that they belong to a different species. Perhaps they would turn your way and look you in the eye—a gaze from your most distant hominid ancestors, the first primates to split off from the other apes and begin the family that produced us. Such are the daydreams paleoanthropologists indulge in as they endure blazing heat, merciless sandstorms, and years of fruitless fieldwork. If the earliest hominids were anything like chimps, bonobos, and other living apes, each species may have numbered in the hundreds of thousands, even millions. But few left fossils behind. Most of their bones were scavenged and scattered by hyenas or other animals, and what little remained rotted. When it comes to early hominids, paleoanthropologists have to make do with a few teeth or skull fragments. Yet paleoanthropologists are learning a lot about our origins. Not long ago, the oldest known hominid was Australopithecus afarensis, a species that walked the savannas of East Africa around 3.6 million years ago and is best known from one well-preserved female skeleton found in Ethiopia in 1974 and nicknamed Lucy. In recent years, paleoanthropologists have found perhaps as many as five species that are older than A. afarensis—in some cases much older. Just last year, Michel Brunet of the University of Poitiers, in France, and his team of explorers announced that amid the sand dunes of the Sahara they had found a species between 6 million and 7 million years old: Sahelanthropus tchadensis. These new fossils have thrown cherished orthodoxies into question. "We saw human evolution as a nice, straight line," says Leslie Aiello of University College London. Now some researchers are arguing that human evolution looked more like a bush, with lots of species branching off in different directions. No new orthodoxy has gained enough strength yet to take over the old one. Instead, there's lots of debate. Some paleoanthropologists, for example, have declared Sahelanthropus to be on the line that led to gorillas, not humans. "That's crazy," replies Brunet, who points to small teeth and other key traits that link the creature with hominids rather than apes. But while Brunet is confident he has discovered the oldest known hominid, he doesn't think it's possible yet to make grand pronouncements about the shape of the hominid tree and its various branches. "You can't say that it's bushy," he says. "Maybe it is; we don't know. Our story has just doubled in time, and we're just beginning to understand it."
