By Jack Eardley
It seems sensible that brain size should relate to primates’ social skills: surely a larger brain is needed to understand rigid hierarchies like the Macaque’s or to live in huge social groups like the Gelada Baboon. According to recent work done by Durham PhD candidate Lauren Powell and collaborators this may not be the case.
Through careful statistical analysis she disputes the ‘Social Brain Hypothesis’ by questioning the correlation between brain size and social group size. Previous work has suggested that primates who live in larger groups and therefore have more complex social structures will have larger brains to accommodate for this.
Not only does Lauren question the link put forward by the ‘Social Brain Hypothesis’ but also the very premise that brain size is a good measure of intellectual capacity and that group size is a good measure of social structure complexity. “The brain is a mosaic of functions,” and because of this, simply measuring brain size is an inadequate and blunt tool for understanding a primates intellect.
Simply measuring brain size is an inadequate and blunt tool for understanding a primates intellect.
Lauren’s work actually finds more evidence to support a link between a species foraging area and its brain size, perhaps due to the mental requirements of navigating larger areas of land.
In interview, Lauren is keen to point out that correlating simple metrics like this can only tell you so much and that studying primate mental capacity should be far more nuanced to reflect the complexity of the brain. Many feats that humans would consider indicative of intelligence such as Chimpanzees using tools to fish for termites or rocks to break into nuts are not considered in this sort of analysis.
Finding links between brain size and foraging area does not answer questions about evolution. How can we know if primates developed larger brains to accommodate larger foraging areas or if they developed larger foraging areas due to larger brains?
Perhaps larger primate groups were established to protect from predators, these then needed larger feeding areas and so larger brains to know their way around. Maybe larger brained primates had a competitive advantage as they were capable of searching for food in a larger area. With current methodology it is only possible, and indeed enjoyable, to guess.
“We hope that our study will stimulate other researchers to study brain evolution with more sophisticated measures of both brain and behaviour.” The nature of the primate and human brain as well as its evolution is a subject whose surface researchers are simply starting to scratch and moving on from simple models will surely allow for a more complete understanding.
In the future, it will become increasingly possible to use growing computer power and sophisticated genetic algorithms to answer these evolutionary questions, using a technique called Ancestral reconstruction. This may allow greater understanding of how primates evolved to their current state and may even help explain the nature and evolution of the human brain.