Human brain did not shrink 3,000 years ago as thought earlier, say researchers

IANS

New York, August 7

As speculated earlier, the 12th-century BCE, a time when humans were forging great empires and developing new forms of written text, did not coincide with an evolutionary reduction in brain size, say a team of researchers refuting the popular hypothesis among the science community.

Last year, a group of scientists made headlines when they concluded that the human brain shrank during the transition to modern urban societies about 3,000 years ago because, they said, our ancestors' ability to store information externally in social groups decreased our need to maintain large brains.

Their hypothesis, which explored decades-old ideas on the evolutionary reduction of modern human brain size, was based on a comparison to evolutionary patterns seen in ant colonies.

Not so fast, said the team from University of Nevada-Los Angeles.

"We were struck by the implications of a substantial reduction in modern human brain size at roughly 3,000 years ago, during an era of many important innovations and historical events, the appearance of Egypt's New Kingdom, the development of Chinese script, the Trojan War, and the emergence of the Olmec civilization, among many others," said anthropologist Brian Villmoare from the varsity.

In a new paper published in Frontiers in Ecology and Evolution, they re-examined the previous dataset and found that human brain size has not changed in 30,000 years, and probably not in 3,00,000 years.

"In fact, based on this dataset, we can identify no reduction in brain size in modern humans over any time-period since the origins of our species," Villmoare said.

The team questioned several of the previous hypotheses that gleaned from a dataset of nearly 1,000 early human fossil and museum specimens.

They noted the rise of agriculture and complex societies occurred at different times around the globe - meaning there should be variation in timing of skull changes seen in different populations.

However, the previous dataset sampled only 23 crania from the timeframe critical to the brain shrinkage hypothesis and lumped together specimens from locations including England, China, Mali, and Algeria.

The previous dataset is also heavily skewed because more than half of the 987 skulls examined represent only the last 100 years of a 9.8-million-year span of time, and therefore don't give scientists a good idea of how much cranial size has changed over time, Villmoare said.

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