Individuals of one species of baboon show a strong preference for seeking out members of a troop possessing characteristics like their own, cozying up to those close to them in age, dominance rank and even personality, researchers say.
The phenomenon, observed in two troops of chacma baboons studied from 2009 to 2014 in the Tsaobis Nature Park in Namibia, is known scientifically as homophily, or "love of the same," say researchers from the University of Cambridge and the Zoological Society of London.
"Within these big troop networks over time social preferences are generally dictated by age, rank, personality and so on," says Alecia Carter of Cambridge's Department of Zoology. "This happens in humans all the time; we hang out with people who have the same income, religion, education, etc. Essentially, it's the same in baboons."
The study, the researchers say, is the first to have followed baboon social network structures for such as extended period of time.
"Our analysis is the first to suggest that bolder and shyer baboons are more likely to associate with others that share this personality trait," says Guy Cowlishaw from the Zoological Society of London, senior author of a study published in the journal Royal Society Open Science.
Previous studies of a wide range of species have suggested time spent in proximity with those displaying like personalities could help strengthen cooperation between individuals, he says.
However, there could be a downside, the researchers note, explaining that previous research they conducted showed baboons of a certain age and personality type - younger, bolder animals - are more likely to be what are dubbed information "generators," those individuals that commonly can solve new challenges in foraging for food, for instance.
If those types of individuals prefer just the company of each other, it presents a risk that acquired beneficial information may be confined solely to other information generators, possibly interfering with the dissemination of new knowledge to the wider troop.
Gender didn't appear to be a barrier to desirable social interactions, the researchers found; females demonstrated a preference for grooming males, offering the service to a number of males in the troop.
That's probably a tactic females use in an attempt to protect their offspring, Carter says.
"Chacma baboon males will often commit infanticide, killing the babies of rivals," she explains. "Female baboons try and get around this by being as promiscuous as possible to confuse the paternal identity - so males find it harder to tell if they are killing a rival's offspring or their own."