Form and Content
In 1974, in Ethiopia’s Afar Triangle, Donald Johanson discovered the bones of a human ancestor that had lived at least 3.5 million years earlier. The bones were from a small female who walked erect but who had a brain size about one-third that of the average modern human. Forty percent of the skeleton was found, making it the most complete fossil of a human ancestor ever discovered older than seventy-five thousand years. The skeleton was named Lucy, after the Beatles song “Lucy in the Sky with Diamonds.” In 1981, with the help of noted science writer Maitland Edey, Johanson wrote Lucy: The Beginnings of Humankind. The book describes the finding of Lucy’s skeleton and discusses how the discovery forced scientists to rethink their theories about human evolution. For example, it suggested that human ancestors walked erect millions of years before their brain size approached the modern norm.
Particularly controversial, however, was Johanson’s decision to create a new species for Lucy, which he named Australopithecus afarensis. Two Australopithecus species were already known, africanus and robustus, and it was commonly thought that africanus was the direct ancestor of the human line. (Species actually in the human line are designated “Homo,” as in Homo erectus; modern humans are Homo sapiens.) Johanson believed that Australopithecus afarensis was the...
(The entire section is 508 words.)