Friday, October 17, 2014

why early humans reshaped their children's skulls

It doesn't take a degree in human anatomy to realise that there is something unusual about the Cohuna skull. With its flat, sloping forehead and prominent brow ridge, it looks distinctly primitive.

For decades, the prehistoric Cohuna skull and others like it have occupied a central and contentious role in answering one of the most important questions in human evolutionary studies: where did our species, Homo sapiens, come from?

Most anthropologists now agree that the skulls don't demand a rewrite of the human evolution text books, but this, paradoxically, has made them all the more intriguing. It confirms that they owe their strange appearance not to the blind hand of evolution but to the guiding hand of humanity. Australia's ancient inhabitants were among the first in the world to deliberately transform the shape of their own skulls - and their motives for doing were probably not as strange as they might at first appear.
The skull was a source of controversy from almost the moment it was ploughed up in a field near the town of Cohuna in Victoria, Australia, in 1925. Some researchers enthusiastically proclaimed its strange shape and the generous coating of minerals encrusted around it showed that it predated all then known human skulls, and must therefore have belonged to one of our earliest ancestors. 

Sceptics, who pointed out it was found in geologically recent soil not far below the surface, were just as certain it did not. They soon won the argument. Genuinely primitive and ancient human skulls were discovered in Africa around this time, and over time anthropologists came to accept that it was there, rather than in Australia, that humanity had evolved long ago. The Cohuna skull was clearly unusual and its anomalous shape was difficult to explain, but it was quietly forgotten….

By now it was possible to estimate the age of fossils using carbon dating: the Kow Swamp specimens were about 9,000 to 13,000 years old, while the Nacurrie skull was about 11,000 years old. The Coobol Creek remains were about 14,000 years old. This makes the fossils prehistoric, just as the enthusiasts in the 1920s had suspected. But the sceptics had been correct too as human fossils found in Africa were dated at between 3 and 4 million years old. Even our species, Homo sapiens, comfortably predates the strange Australians, as skulls with all the features of modern humans are found in rocks as old as 160,000 years.

The age of the Australian skulls did raise a question, though. Their distinctive sloping foreheads and prominent brow ridges are very like those of an ancient human species called Homo erectus, that lived between 2 million and 140,000 years ago. Why did the Australian skulls look so eerily like this long-dead species? bbc

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