Primate Brains Follow Predictable Pattern, Study Shows

Primate brains develop in a predictable pattern, according to a study published in the Journal of Neuroscience.

Using computer modeling, the researchers clearly demonstrated that the enlargement of areas of the human brain related to advanced cognition represents a pattern seen in primates of all sizes.

According to the press release outlining the study, the neuroscientists from Monash University and the Universidade Federal de Janeiro found that "differences between primate brains -- from the tiny marmoset to human -- can be largely explained as consequences of the same genetic program."

The discovery suggests that the development of neural circuits responsible for uniquely human traits, including speaking and making complex plans, emerged naturally through the evolution of larger brains.

"We have known for a long time that certain areas of the human brain are much larger than one would expect based on how monkey brains are organised," Marcello Rosa from Monash University's School of Biomedical Sciences said in a press release. "What no one had [realized] is that this selective enlargement is part of a trend that has been present since the dawn of primates."

The scientists relied on publicly available brain maps, MRI imaging data and model software to compare the sizes of brain areas in humans and three monkey species -- marmosets, capuchins and macaques. In doing so, they discovered that the lateral prefrontal cortex (key to long term planning, personality and decision-making), and the temporal parietal junction (related to self-awareness), expand disproportionately in comparison to the rest of the brain.

However, the researchers found, these areas of the brain grew disproportionately in a predictable manner.

"We found that the larger the brain is, the larger these areas get," Tristan said.

In comparing the smaller marmoset to the larger macaque, for instance, the prefrontal and temporal junction grew larger in comparison to the rest of the cortex -- a pattern repeated when comparing macaques to humans.

"This trend argues against the view that specific human mutations gave us these larger areas and advanced cognition and behaviour, but are a consequence of what happens in development when you grow a larger brain," Tristan said.

The pattern was still present even in primate species that evolved independently of one another.

"If you compare the capuchin of South America and the macaque of Asia, their brains are almost identical, although they developed on opposite sides of the world," Rosa said. "They both reflect the genetic plan of how a primate brain grows."

Going forward, Tristan hopes to collaborate with zoos to examine whether if chimpanzees and gorillas -- humans' closest primate relatives -- boast brains organized according to the recent observations.