for National Geographic News
Scientists have been unraveling the mysteries of when early hominids first left Africa, where they went, how many hominid species there were, and how they relate to modern humans, for more than a century.
A skull recently found in Indonesia adds a valuable piece to the fossil record, but scientists differ about where it fits in the human family tree.
The skull, which scientists call Sambungmacan 4 (Sm 4), was found in the Sambungmacan district of central Java, Indonesia. It is that of a middle-aged or slightly younger male Homo erectus who had probably suffered and recovered from head wounds. Two partial skulls and the fragment of a tibia had previously been discovered in the area.
Homo erectus, and perhaps other early hominid [see side bar for definition] species, began leaving Africa sometime around 2 million years ago. Fossil remains have been found in Asia, the Middle East, and Europe.
Indonesia, an island nation in southeast Asia, is the site of some of the earliest Homo erectus remains yet found. The relatively abundant fossil material provides scientists with an opportunity to study the evolution of the species and how it relates to modern humans.
Scientists led by Hisao Baba, an anthropologist at the National Science Museum in Tokyo, analyzed the Sm 4 skull using digital visualization techniques, and compared it with other skulls found in Java.
Writing in the February 28 issue of the journal Science, Baba and colleagues argue that morphological characteristics of early H. erectus in Java, represented by fossil finds from Trinil/Sangiran, more closely resemble those of modern humans. Fossil material from Ngandong, which has been dated to anywhere between 25,000 to 50,000 years old, suggests that Java H. erectus had gone off on an evolutionary tangent of its own, developing distinct features that are not shared by modern humans.
They conclude that Javanese populations became progressively more isolated from other Asian H. erectus populations, and made minimal contributions to the ancestry of modern humans.
At one time scientists considered it possible that modern humans were the direct descendants of Asian Homo erectus. That idea has been discarded by many scientists who now think that while African H. erectus may be ancestral to H. sapiens, Asian H. erectus was an evolutionary dead end, rather than the immediate precursor to modern humans.
Still other scientists believe that the African version of H. erectus is different enough that it belongs in a separate species category called Homo ergaster.
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