New evidence strongly suggests that the human race migrated from its African cradle to Asia nearly 1 million years earlier than most scientists believed, a discovery that challenges some long-held beliefs about key turning points in human evolution.
In a paper presented Wednesday at a meeting of the American Association for the Advancement of Science in San Francisco, Carl Swisher III of the Institute of Human Origins in Berkeley, Calif., reported that skull fragments of Homo erectus found on the Indonesian island of Java are up to 1.8 million years old, as old as the oldest Homo erectus fossils found in Africa.
This may mean, he said, that the early human beings commonly lumped together under the species name Homo erectus may have belonged to two or more separate species that evolved independently from a common ancestor.
Although most anthropologists believe that the human race originated in Africa, the new measurements open the possibility that, although man’s prehuman ancestors began in Africa, different variants of the primate genus Homo may have independently evolved in Africa, Europe and Asia.
Homo erectus is the name commonly given to a group of primates many anthropologists believe to be the first entitled to be called human beings.
From Homo erectus evolved Homo sapiens and its present-day subspecies, Homo sapiens sapiens. Somewhere along the way, either as an intermediate or an offshoot of the evolutionary line, Neanderthals arose, flourished and died out about 35,000 years ago.
But none of the evolutionary connections among human ancestors are clear.
“This is certainly going to prompt a lot of discussion and theorizing,” Swisher said.
The skull fragments came from two sites in central Java. The first, the skull cap of a child, named the Mojokerto child, was found in 1936 near the village of Perning. Two other sets of skull fragments, called Meganthropus, were found near Sangiran in the late 1970s.
Until now the oldest human remains in Asia were believed to be about 1 million years old. By comparison, the oldest human remains in Africa were estimated at about 1.8 million years.
Many anthropologists believed that the age difference between the earliest African and earliest Asian Homo erectus fossils implied that the species started in Africa and then radiated much later to other continents.
But this theory has always troubled some scientists.
For example, Homo erectus in Africa devised specialized, two-faced stone cleavers and hand axes, collectively known as the Acheulean tool kit, that are frequently found at Homo erectus sites in Africa but not in Asia.
If Homo erectus developed in Africa, invented these useful tools and then set out to colonize Asia, why did he not take his tools along?
If, on the other hand, separate branches of the Homo erectus tree evolved simultaneously in Africa and Asia, as the new fossil dates seem to suggest, this problem would be explained: The founders of the Asian branch left home before their African cousins had had time to invent Acheulean tools.
The new date of the Mojokerto child, Swisher’s group has determined, is about 1.81 million years, and the Sangiran fossils are about 1.66 million years old. The oldest African Homo erectus fossils, found at Koobi Fora in Kenya, has been dated at about the same age as the Mojokerto child.
Swisher and his colleagues did not analyze the fossils themselves but determined the ages of the pumice and other volcanic rock in which the fossils were embedded when they were excavated.
They used an extremely sensitive method that Swisher said yields dates accurate to within about 70,000 years.
