A new study suggests that the brains of primates are different depending on their status as leaders or followers. But are these 'specialized brains' the result of genetics or an adaptation to the individual's role in life?
Researchers from the University of Oxford were curious to learn if social dominance could be correlated to unique signatures in the brain. To that end, they looked at the fMRI brain scans of 25 macaques. The results were surprisingly clear.
The monkeys at the top of social groups exhibited three distinct differences: a larger amygdala, hypothalamus, and raphe nucleus. In subordinate monkeys, clusters of brain regions in the striatum were larger.
The BBC explains the results:
At either end of the social ladder, compared to monkeys in the middle, the activity in all these different brain regions was more synchronised. The researchers believe these areas together constitute brain circuits that are crucial for negotiating social situations - interpreting social and emotional cues, learning the value of certain actions, and so on.
Dr [MaryAnn] Noonan said it was particularly interesting to see different brain regions expanded at the top and the bottom of the social ladder, indicating that dominance isn't simply about being physically stronger and having an altogether bigger brain.
"It suggests that at either end [of the hierarchy], you really need a specific set of skills to be successful, and those skills are making higher neural demands on those areas of the brain," she told the BBC.
"In the animal kingdom, you might think that being dominant is all about aggression - I'm the bigger monkey, bugger off the rest of you.
"But all of this put together means that dominance might actually depend not only on aggression and physical strength, but also on forming bonds and making coalitions - and being quite smart about placing your loyalties."
This said, the researchers can't be sure if these differences were present at birth — thus predisposing the monkeys to a particular social rank — or whether they reflect the ongoing changes in the brain's organization based on the demands of maintaining a high social rank.
According to Noonan, it's probably a bit of both, adding that, "because they're both really important mechanisms to have on board. You can imagine if you've come from 'good stock' within the monkey world, and your dad was really strong and muscly, you'll inherit those genes, and that might set your brain up in a certain way. But of course you're going to have to be plastic, in order to succeed and survive. You'll have to be adapting your behaviour and therefore your brain has got to adapt too."
It's probably safe to assume that a similar effect exists in humans and other primates. But the conclusions are not at all surprising. The variables responsible for social hierarchies are vast and complex — something that couldn't possibly be explained away in a simple fMRI scan.
Read the entire article at the BBC. And check out the entire study at PLOS: "A Neural Circuit Covarying with Social Hierarchy in Macaques".
Top image: Dawn of the Planet of the Apes
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