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Tasmanian clues to human evolution.

Tasmanian clues to human evolution

Skeletal studies of the aborigines who have inhabited Tasmania for more than 30,000 years (SN:4/8/89, p.223) present anthropologists with a problem. Some researchers cite anatomical links -- often based on measurements of the brain case and teeth -- between Tasmanian and Australian aborigines, suggesting the former group migrated from Australia across an ancient land bridge to their island home, about 200 miles to the south. Other investigators, focusing on different cranial features, find a weak connection between Tasmanian and Australian aborigines. Instead, they group Tasmanians with Melanesians living on islands northeast of Australia.

This South Pacific paradox stems from the different skeletal traits and statistical methods relied on by opposing scientific camps, asserts anthropologist Colin Pardoe of the Australian Institute of Aboriginal Studies in Canberra. However, Pardoe reports in the February CURRENT ANTHROPOLOGY, a comparative analysis of dozens of seemingly minor skull parts indicates that Tasmanian and Australian aborigines share far more anatomical similarities than expected, considering that the two populations have remained separate for 8,000 years.

This finding challenges the widespread assumption that many anatomical differences among human populations arose when great distances or geographic barriers prevented the passing of genes from one group to another through mating, thus allowing random genetic changes and local environmental influences to mold the anatomy of isolated peoples. On the contrary, Pardoe argues, mating across two populations may promote greater anatomical differences between the groups.

Tasmanians have endured the longest genetic isolation of any human group, Pardoe says. When rising seas swamped their land bridge to Australia 8,000 years ago, he maintains, islanders could not get to the mainland by canoe or raft.

Pardoe looked for the presence or absence of 35 minor anatomical features on the skulls of aborigines from Tasmania and regions throughout Australia. Unlike more prominent traits such as skull breadth, these features -- including tiny bones formed by cranial sutures and small bridges of bone caused by excess growth -- confer few survival advantages and mainly evolve randomly, outside the influence of behavioral adaptations to a particular environment, Pardoe contends.

His comparisons of the proportions of these traits indicate that Tasmanians display the most similarity to aborigines from southern Australia and appear far more similar to Australians in general than expected in so isolated a population, he says. Moreover, Tasmanian and Australian skulls show cranial differences roughly comparable to those observed among pairs of island-mainland groups with much more contact, such as Aleutian islanders and Alaskan Indians.

The results support the controversial notion that separate populations of anatomically modern humans evolved simultaneously in several parts of the world, beginning as early as 1 million years ago (SN:2/27/88, p.138), says Milford H. Wolpoff of the University of Michigan in Ann Arbor. Wolpoff asserts that those who argue for a single, more recent origin of modern humans in Africa wrongly assume that isolated ancient human populations would develop so many anatomical differences over time that several Homo species would have evolved.

Christopher B. Stringer of the British Museum of Natural History in London, a leading advocate of the African-origin theory, has not yet seen Pardoe's report, but he told SCIENCE NEWS that the new data may not clarify variations in the anatomical evolution of different groups. For example, Stringer says, many skeletal changes evolved within a few thousand years in some prehistoric populations, such as early New World Indians, whereas few appeared among Neanderthals over a 100,000-year time span.
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Title Annotation:evidence that Tasmania's aborigines originated in Australia rather than Melanesia
Publication:Science News
Date:Feb 16, 1991
Words:581
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