Primate brain study gives new clues to human evolution

21 September 2020

We'll now be able to find out more precisely when the temporal lobe began to enlarge and be inherited by early humans

A new technique to measure primate brains developed at The ANU could give scientists a better understanding of human evolution.

The new research, by ANU PhD candidate Alannah Pearson, will enable scientists for the first time to accurately compare brain evolution across different primate species - both living and fossilised.

Ms Pearson studied the Middle Cranial Fossa (MCF) - a tiny butterfly-shaped bone at the base of the skull - and its relationship with the size of the temporal lobe in primates.

Her results showed the MCF to be a very reliable predictor of temporal lobe volume as far back as 35 million years.

"The temporal lobe is the only region of the brain that is larger in humans than any other living primate," Ms Pearson said.

"It's a part of the brain associated with things like memory, language and emotion, but no estimates of fossil temporal lobe size has been possible before.

"We've not been able to examine when temporal lobe size might have increased during evolution, or even if modern humans are the only species that had these larger temporal lobes."

Using MRI Imagery of the brains of living humans, as well as living monkeys and apes, Ms Pearson was able to calculate the actual volume of the temporal lobe and found it closely matched the size predicted by the MCF.

Ms Pearson also examined fossil and modern skulls of 23 primate species across the evolutionary range from 35 million years ago to the present day.

"The same skull anatomy was present in all 23 primate species," Ms Pearson said.

"I found that in 11 different living primate species, the temporal lobe volume could be predicted to within 1 standard error - statistically, that's a very close margin when you're studying many different species.

"This also means that even over 35 million years of primate brain evolution, temporal lobe size is still closely related to MCF size, so now we'll be able to find out more precisely when the temporal lobe began to enlarge and be inherited by early humans.

"Establishing this would provide an evolutionary time-line of human brain development."