Study maps missing piece of brain evolution  

The temporal lobe – a key area of our brain responsible for our memory and communication – could also reveal hidden clues about how human brains have evolved over time, according to a new study from The Australian National University (ANU).  

PhD scholar Alannah Pearson used CT scans to compare 3D virtual skulls of several of our earliest ancestors, as well as all living species of great apes. The ANU study is the first of its kind comparing temporal lobe size to brain size. 

“I was interested in whether the temporal lobe changed shape or size as the brain developed,” Ms Pearson said. 

“The theory has been that the size of the temporal lobes increased with more complex social behaviour – so extended communication in humans, or the exploration of new environments,” Ms Pearson said. 

“We also looked at changes to the proportions of the temporal lobe in both great apes and our human ancestors. 

“Given the complex lives of modern humans, you might expect the temporal lobe would be larger to accommodate this complexity. Instead, we found fossil Homo sapiens likely had smaller temporal lobes for their brain size, meaning that other regions of the brain likely expanded to play greater roles. So, brain and temporal lobe size is probably not as important in this scenario as efficiency.” 

Ms Pearson said the most significant changes in the temporal lobe occurred in two ape-like early hominins – the group that includes modern humans – as well as chimpanzees and bonobos. 

“Australopithecus and Paranthropus were among the first to move away from dense forests and into savannahs. This likely would have required an expansion of the temporal lobe as they encountered new environments and more complex social structures,” she said. 

The temporal lobe is one of the parts of the brain that has changed the most over time. 

“Several factors may have contributed to this,” Ms Pearson said. 

“There are popular theories around brain evolution – that the brain changes size and proportions as the skull changes, that it changes in size due to greater social complexity and that it changes in size along with changes to the environment. All three likely played a part in the changes we’ve seen to the temporal lobe.” 

The study has been published in American Journal of Biological Anthropology.