Picking your brain: the new techniques tracing brain evolution

Brains – like most soft tissue – are tricky to study. Because they don’t fossilise, scientists are left with very little clues when it comes to shape, size and anatomy.

That’s where endocasts come in. These moulds of the inside of ancient skulls can be used as a stand-in to help scientists study the human brain and its evolution.

An international team of researchers, including ANU PhD scholar Alannah Pearson, set out to determine just how reliable endocasts are when it comes to shedding light on the anatomy of the brain, and in turn revealing more about the traits of our early ancestors.

Pearson says endocasts can show the grooves and ridges of the brain, as well as different lobes of regions that can signify anatomical functional and species-related differences.

“By studying the changes in these grooves and ridges in the different lobes of the brain, we can start to see how things like communication and complex thought processes began to take shape,” she says.

“The moulds are typically made using CT scans and high-tech computer software to create a virtual 3D replica of the skull.”

These moulds can give us all sorts of important clues about human evolution. For example, we know by studying endocasts that in early Homo Sapiens, the size and position of Broca’s Area – the part of the brain responsible for our ability to produce language – was very similar to our own.

To complicate matters, when studying these types of ancient fossils experts like Pearson and her colleagues are rarely dealing with a complete skull, but instead faced with one that’s very fragmented and broken.

“This creates issues,” Pearson says.

“Determining the divisions of the brain into lobes often becomes an estimation based on the skill of the researcher – they’re relying on their own knowledge of brain anatomy and the species the skull belongs to.”

To get around this, the team, led by Dr Antoine Balzeau at the Museum national d’Histoire naturelle in France, looks at the marks on an endocast image of a living person.

The experts work ‘blindly’, as they’re forced to do with fossils. They then compared their results to the real thing using different brain imaging techniques to see if the positions of the marks and furrows matched up.

“Our study used predictions from this group of experts and mathematical models to create a new way to estimate the placement of these imprints that line the inside of a skull,” Pearson says.

“We also found the base of the skull and frontal lobes are good areas to target to get a more accurate prediction, as the groves and ridges are often naturally clearer in these areas.

“This study should help add to our awareness of the limits of their interpretations and to better understand the relationship between the endocast and the brain of humans, current or fossilised.”

It’s lucky we have such a team of brainy experts on the case!