It is one of the fundamental mysteries of human evolution. When did the first apelike creatures begin to walk upright? Scientists believe this transformation probably occurred between 4 million and 6 million years ago, but until recently they had no fossils to back up their hypothesis. In 1994 researchers reported that they had found teeth and other fragments of a 4.4 million-year-old hominid in Ethiopia. But without key bones from below the waist, they could not say for sure how the animal moved.
Now, less than a year later, another team of paleontologists, led by Meave Leakey from the National Museums...