Day By Day

Saturday, February 24, 2007

Redating Human Origins

Through the Twentieth Century the general trend in human evolutionary studies was to extend estimated dates for important developments farther into the distant past. This was in large part due to the continued discovery of ever-more-ancient remains, but there was a built-in assumption that dates would continue to be pushed back indefinitely and a related competition among scholars to find the earliest or the first evidence of human characteristics in ancient fossils.

By the end of the last century there was broad agreement that the evolutionary line leading to humans had diverged from that leading to modern chimpanzees around seven million years ago while our most significant progenitor, Homo Erectus, had emerged in East Africa about two million years ago and had colonized the rest of Eurasia from there, and that "anatomically modern" humans had emerged somewhere in Africa around 200,000 years ago.

Recently, however, a number of scholars have reversed the trend of earlier studies and have suggested much later dates for some of these developments.

Perhaps the most significant revision came last year with the redating of East African Homo Erectus remains, showing them to be about a quarter of a million years later than had previously been thought. What is more, the redating showed that the African fossils were significantly younger than other Homo Erectus remains found in Eastern Europe and Asia.

Read a technical analysis of the redating here and a more speculative piece here.

Now comes a couple of studies that significantly reduce the estimate of when the human lineage diverged from that of chimpanzees. One found that the divergence took place no more than 5.4 million years ago, the other estimated four million years for the divergence. Read about it here.

And finally, there has been a redating of Clovis artifacts, long thought to be fashioned by the first humans to enter the Americas, showing that they are younger than some other assemblages. Read about it here.

The point of all this is that for several decades a scientific consensus existed in favor of ever older dates for human remains and this expectation biased the scientists who reported evidence. They weren't dishonest, simply biased in favor of the consensual position. Now that the consensus has been broken, evidence is being re-evaluated and new positions are emerging.

Could it be that a similar bias might be operating in the field of environmental studies?

Just asking.

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