London: Scientists have found that being popular actually runs in the family - at least for monkeys!
A two-year study of rhesus macaque monkeys found individuals who were social and popular tended to have descendants with a similar nature.
The monkeys studied were a free-ranging population of macaques descended from a 1938 release of monkeys from India on undeveloped 38-acre Cayo Santiago Island, off the eastern coast of Puerto Rico.
The team`s analysis of the troop`s family trees and genetics, suggested that being social was a trait passed on by natural selection.
"If you are a more social monkey, then you`re going to have greater reproductive success, meaning your babies are more likely to survive their first year," post-doctoral research fellow Lauren Brent, who led the Duke University study said.
"Natural selection appears to be favouring pro-social behaviour," Brent said.
The analysis combined sophisticated social network maps with 75 years of pedigree data and some genetic analysis.
Field researchers compiled four or five hours of data per individual, logging grooming, proximity and aggression.
From that, the team built web-like network maps to analyse pro-social and anti-social interactions.
They also looked at the maps for a measure they called `betweenness` - the shortest paths between individuals - and `eigenvector`, a friends-of-friends measure that shows how many friends each friend of an individual has.
"The really `popular` monkeys would have a high eigenvector, or a really big friends-of-friends network," Brent said.
"There were also less-popular outliers who had fewer social interactions and a lower eigenvector - they`re sort of the dorks," Brent said.
Brent said comparing the observation results with the family trees revealed many of the behaviours ran in the family.
The study found aggression did influence reproductive success, with monkeys who were the most aggressive and those who were the most passive having better reproductive success than the monkeys in the middle.
The team also collected blood samples and analysed two genes in the monkeys` serotonin system, which carries signals between nerve cells and which in humans is acted on by antidepressant drugs.
The researchers found variability in the two genes - one that makes serotonin and one that carries it around - was associated with differences in grooming connections between the monkeys.
The study was published in journal Nature Scientific Reports.