The main lines of Darwin's theory--as well as the evidence which has emerged subsequently to support it--can be seen at a glance in the image of the three skulls to the left. The emergence of our distinctive species characteristics must have proceeded in gradual stages over an extended period of time. This line of thought led to a search for the expected intermediate forms between apes and humans--the famous concept of a "missing link" popular in nineteenth-century journalism.
Influenced by Darwin's work, Dutch naturalist Eugene Dubois set out in 1891 to confirm the theory and to find the "missing link." Dubois differed from Darwin in assuming that humans had evolved in tropical Asia, so he searched in Java. He found a fossil skull cap and a thigh bone near the Solo River in Java which seemed to him mid-way between apes and humans. He named his find "Pithicanthropus erectus" or "erect ape-man." The public named it "Java Man." As more information accumulated, the species was re-named "Homo erectus"--"erect or upright man." The earliest specimens of this species have since been found in Africa.A composite Homo erectus skull is shown above. According to available evidence, it was the first human species to migrate out of Africa and adapt to a wide variety of environments in Europe and Asia.
Subsequent discoveries in the twentieth century have confirmed Darwin's guess. We now have a rough picture of the human family tree as far back as 4.4 to 5 million years ago.
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