Late in the nineteenth century, the Dutch physician Eugene Dubois traveled as a military doctor to the Dutch East Indies (now Indonesia) in search of the fossil remains of human ancestors. He was following the predictions of Ernst Haeckel, who anticipated a prehuman ancestor that walked upright but did not speak (“Pithecanthropus alalus”), and surmised that the tropics would be the origin of modern humans. His search was rewarded in the 1890s when workers discovered the skull cap of an early human at the site of Trinil along the Solo River of Java. From the same locality, but perhaps younger in age, came upper leg bones as well. Dubois named the fossils Pithecanthropus erectus, upright ape-man.