Homo erectus shows staying power on Java.
H. erectus, now estimated to have inhabited the Indonesian island of Java until sometime between 27,000 and 53,000 years ago, died out as H. sapiens more successfully exploited local Stone Age environments, assert Carl C. Swisher III of the Berkeley (Calif.) Geochronology Center and his colleagues. Many researchers have argued that a similar scenario played out in Europe and the Middle East, where Neandertals lived at the same time as H. sapiens before going extinct around 35,000 years ago.
"It looks like independent [H.] erectus and [H.] sapiens lineages evolved in Southeast Asia," holds study participant Susan C. Anton, an anthropologist at the University of Florida in Gainesville. "It wouldn't have taken a huge technological or intellectual advantage for one species to have replaced another over a number of generations."
Investigators familiar with the new results agree on two points: The revised dates require further verification and, if they hold up, they will fuel rather than resolve the ongoing debate over the nature of modern human origins (SN: 6/20/92, p. 408).
Most prior age estimates for these H. erectus finds on Java fell between 100,000 and 250,000 years ago. Given that timing, some researchers argued that in Southeast Asia, H. erectus evolved into H. sapiens.
The revised ages indicate that H. erectus survived so late on Java-at least 250,000 years longer than on mainland Asia and perhaps 1 million years longer than in Africa-that it could not have been a human precursor in Southeast Asia.
Swisher's team estimated ages from analyses of the rate of uranium decay in four animal teeth found in sediment at two sites on Java that had yielded H. erectus fossils more than 60 years ago. Uncertainty over whether the teeth absorbed uranium quickly or slowly after being buried led to the spread in age estimates that the scientists report in the Dec. 13 Science.
Modern humans originated in Africa more recently than 200,000 years ago and then migrated throughout the world, in Anton's view. Separate H. erectus and H. sapiens lineages could have coexisted in several regions, she notes.
For instance, H. erectus may have settled Australia more than 100,000 years ago (SN: 9/28/96, p. 196), followed by H. sapiens.
"The new dates for Homo erectus on Java are remarkably young," remarks anthropologist Christopher B. Stringer of the British Museum in London, a proponent of relatively recent African origins of modern humans. "I'm inclined to view them favorably, but this [new study] isn't the last word."
Simultaneous H. erectus and H. sapiens populations in Southeast Asia may have stayed totally separate or interbred to such a limited extent that H. erectus genes were not passed on to later human groups, Stringer holds.
Anthropologist Milford H. Wolpoff of the University of Michigan in Ann Arbor disagrees. Wolpoff and other proponents of multiregional evolution argue that H. erectus fossils actually belong to an anatomically diverse form of H. sapiens that arose in several parts of the world over the past 2 million years.
"Even if these new dates on Java are correct, the anatomical features of available fossils still support multiregional evolution," Wolpoff contends. For instance, commonalities in the shape and dimensions of Javanese H. erectus and Australian H. sapiens craniums signify close genetic ties, he says.
"The proper way to define both a living and a fossil species is the $64,000 question," Anton states.