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Science And Nature

Shape of mind has barely changed in past 160,000 years

An analysis of fossils suggests changes in the form of the braincase during human evolution were associated with alterations in the facial skin, instead of changes in the mind itself

Humans 1 August 2022

By Luke Taylor

Digital restoration of fossil child and adult crania

Digital restoration of child and adult crania from 160,000 years back

M. Ponce de Len and Ch. Zollikofer/Univ. of Zurich

The physical transformation of the human cranium in the last 160,000 years was probably driven by alterations in the facial skin resulting from lifestyle changes, not from the evolution of the mind itself as previously thought, a report has found.

The cranium, or braincase, of early modern humans dating back to 200,000 years isnt much different in proportions from those today, but includes a significantly different shape, suggesting that the mind is becoming rounder as time passes.

The best hypothesis is that changes in behaviour, like the development of tools and art, caused the form of the Homo sapiens brain to improveand, subsequently, the skull that protects it.

But fossil evidence is scarce and there are lots of interacting forces at play. It really is simple for a skull with a big face to accommodate a big brain, for instance, but a little face complicates matters.

To research the complexities behind the transformation of the braincase, Christoph Zollikofer at the University of Zurich in Switzerland and his colleagues digitally restored the skulls of 50 hominins recovered in Ethiopia and Israel, including H. sapiens along with Homo erectus and Neanderthal specimens for comparison. The 3D types of the fossils were then weighed against 125 modern human specimens.

Comparing the braincases of early modern human children with adults for the very first time allowed the researchers to isolate the brains role in the evolution of the skull.

The team was surprised to get that as the size and proportions of the skulls of H. sapiens children from 160,000 years back were largely much like infants today, the adults looked remarkably dissimilar to those of modern adults, with a lot longer faces and much more pronounced features.

Human faces continue steadily to grow before age of around 20, but the mind reaches around 95 % of its adult size by age 6.

If the fossil children with near fully developed brains resemble living ones, but fossil adults had completely different skulls, we are able to eliminate that brains have changed significantly in form, says Zollikofer. And when its not the mind driving this change, we should look for another thing, like breathing, eating or moving.

The researchers cautiously hypothesise that changes in diet or perhaps a reduced dependence on oxygen might have been responsible.

Faces in modern humans are far smaller, with subtler indentation, than those of these ancestors. Studies also show that this change accelerated when hunter-gatherers became agriculturalists around 12,000 years back and ate softer foods, probably because of less loading on the skull from chewing.

The authors are to remain cautious within their hypotheses, says Chris Stringer at the Natural History Museum in London.

There’s little proof major dietary changes between your Middle and Late Stone Age when these changes occurred, he says. Of the numerous possible causes, a decrease in oxygen intake could possibly be much more likely as humans are suffering from smaller ribcages and also have less lung capacity.

Journal reference: PNAS, DOI: 10.1073/pnas.2123553119

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