Asian hominids make a much earlier entrance.

Members of the human evolutionary family left Africa and reached eastern Asia 800,000 years earlier than previously thought, according to a report in the Feb. 25 SCIENCE.

The new estimate comes from a redating of three Homo erectus specimens from the Indonesian island of Java. Local collectors found a skullcap of a child at one site in 1936 and partial skulls of two individuals at another site in 1974. The first skull now dates to about 1.8 million years ago, the latter specimens to approximately 1.6 million years ago.

Car1 C. Swisher III, a geochronologist at the Institute of Human Origins in Berkeley, Calif., and his colleagues analyzed the relative proportions of two forms of argon in the hominid-bearing sediment from the Indonesian sites to establish new dates for the finds,

Many anthropologists express surprise that H. erectus ventured to the far reaches of Asia so early. However, contrasting theories of how the Homo lineage evolved--which rely on analyses of skeletal anatomy--remain unchanged in the wake of the new study (SN: 6/20/92, p.408).

"It shocks me that hominids [members of the human evolutionary family] lived outside Africa that early," asserts David W Frayer of the University of Kansas at Lawrence. "We'll have to see if these dates hold up."

Frayer and others would prefer age estimates generated from sediment that still clings to the Indonesian bones, but Indonesian officials barred the removal of any material from the fossils, Swisher says. Comparable results at the two sites, located about 150 miles apart, compellingly support the new dates, he argues.

H. erectus apparently reached Asia before the appearance of stone choppers and hand axes in Africa around 1.4 million years ago, Swisher holds. This helps explain why no such artifacts have emerged from Asian sites, he maintains.

African fossils formerly assigned to H. erectus may belong to a separate species that led to modern humans, Swisher suggests. In this scenario, championed by Bernard Wood of the University of Liverpool in England, H. erectus reached an evolutionary dead end in Asia.

G. Philip Rightmire of the State University of New York at Binghamton disagrees, based on his anatomical comparisons of Asian and African fossils.

"Erectus originated in Africa and then pushed out to Asia in pulses of movement," he argues. "The surprising new dates indicate that these migrations, and the Homo lineage itself, have more ancient roots than we thought."

Reasons for the migration of African H. erectus, often linked to the production of versatile hand-axes, now seem unclear, Rightmire contends. And much uncertainty surrounds the relationship of the Homo lineage to African australopithecines, which consist of the earliest hominid species. If H. erectus left Africa by 1.8 million years ago, its ancestor must have evolved simultaneously with various australopithecines, Rightmire notes.

Milford H. Wolpoff of the University of Michigan in Ann Arbor offers a third interpretation of the Java dates. Wolpoff lumps all H. erectus fossils into an anatomically diverse group of H. sapiens that evolved in several parts of the world starting about 2 million years ago.

"These new dates tell us that primitive H. sapiens left Africa much earlier than we thought," he holds.

Recent finds of simple stone tools at a Javanese H. erectus site that may date to 750,000 years ago suggest that Asian hominids probably concentrated on cutting bamboo with quickly produced implements, Wolpoff asserts; knowledge of hand axes may simply not have been put to use. A related report, published in the March 3 NATURE, concludes that H. erectus and H. sapiens may have lived simultaneously in China for a short time.

Measures of the rate of uranium decay in animal teeth uncovered last year in the same deposit as a H. sapiens skull place the finds at a minimum of 200,000 years old, assert Chen Tiemei of Peking University in Beijing, China, and his coworkers. Some Chinese H. erectus remains date to 300,000 years old or less.