A New Key to the Family Tree

By MICHAEL D. LEMONICK

The bones unearthed at Teotihuacan are plenty ancient, but there's old and then there's old--and a find announced by South African scientists last week makes A.D. 150 seem like yesterday. Researchers at the University of the Witwatersrand reported that they've discovered the skeleton of a human ancestor that could be as much as 3.5 million years old.

That's even older than the celebrated Lucy, and comes from a time when humans still had many apelike characteristics. Best of all, this skeleton is almost complete; it even comes with a skull. There is no need to mix and match different specimens to guess what the entire creature looked like (Lucy, for example, was only 40% complete). Once the skeleton is fully excavated in a year or so, experts should be able to pin down the relative sizes of different body parts and see just which of the creature's features were apelike and which were human. It is, says paleontologist Alan Walker of Pennsylvania State University, "perhaps one of the best finds ever."

That's true even if, as some experts suspect, the specimen is really as little as 2.5 million years old. Complete skeletons are so rare that even such a relative youngster will inevitably flesh out the book of human evolution as few discoveries ever have. Says William Kimbel, science director of the Institute of Human Origins at Arizona State University: "It will give us what we got from Lucy, and more."

--By Michael D. Lemonick. Reported by Andrea Dorfman/New York

With reporting by Andrea Dorfman/New York