Washington: New research has provided a glimpse into how our male ancestors may have jockeyed for power and passed it on to their male offsprings.
If you’re a male born to a father who’s a strong and enduring community leader, you’re far more likely than your less fortunate peers to become a leader yourself, due to the wide range of social advantages accruing from your dad’s position.
But if your old man isn’t a leader, other men in your community are more likely to take you under their wing than your sisters, lavishing attention on you and showing you the ropes.
According to Susan Perry, UCLA primatologist, this is also the social structure that prevails among white-faced capuchin monkeys, the cute little New World primates, associated in popular culture with organ grinders.
“Offspring, especially male offspring, raised in a group in which their father is the alpha male, throughout their juvenile phase enjoy a host of advantages over less fortunate monkeys,” Perry said.
“A stable, peaceful family environment may have been important to the well-being and future success of children among our remote ancestors, just as it is to children today,” she said.
Widely known in popular media for their cleverness, dexterity and trainability, capuchins enjoy a distinction that makes them especially compelling to scholars of the evolution of behaviour.
The cat-sized primates have the largest brain-to-body ratio among non-human primates, making their behaviour particularly relevant for understanding the evolutionary history of their big-brained relatives — the humans.
“There are a lot of reasons to suspect that the same selective forces that shaped humans also shaped capuchins, causing both species to share features such as complex political behaviour and culturally transmitted social rituals,” Perry said.
Since 1990, Perry, her husband Joseph Manson, also a UCLA anthropologist, a University of Iowa faculty member, and 122 students, volunteers and copiously trained locals have spent approximately 79,000 hours observing 444 capuchins that make up 11 social groups in Costa Rica’s Lomas Barbudal Biological Reserve.
With data on five generations of these animals, which can live into their 50s, Perry’s Lomas Barbudal Monkey Project is the world’s most detailed study of any natural primate population.
In fact, no other study has so thoroughly documented the details of the lives of so many members of a single species of long-lived mammals.
Perry’s latest findings explore the social dynamics of capuchins, who form cooperative groups with an alpha male, several subordinate males and many females.
The average size of these groups in the Lomas reserve is 19 monkeys, Perry has found. The alpha males rise to their position — and defend it — by fighting off other males with the help of allies.
Initially, females mate exclusively with the alpha male, Perry said.
Extraordinarily, subordinate males wait to mate until the alpha male’s daughters reach sexual maturity, a process that takes an average of six years.
The regimes of most alpha males last about a year, but regimes at Lomas have lasted for as long as 18 years and for as little as a fraction of a day.
Following a changing of the guard, the new alpha male immediately kills all infants that have not been weaned.
In fact, infanticide in this manner is the leading cause of death for infant capuchins. Without nursing infants to care for, the females in the overthrown group quickly return to a fertile state and eventually come around to mate with the new alpha male.
“A marauding male doesn’t know how long he’s going to be in the alpha position, so he really needs to hurry up and start producing babies if he is going to have any hope of protecting them long enough to see them into adulthood,” she said.
As destructive as a changing of the guard is for young capuchins, a stable home life is equally as beneficial, Perry reports.
Results from Lomas indicate that 63 percent of males who grow up in groups that are demographically stable because of a long-enduring alpha male become alpha males when they leave the proverbial nest, Perry reports.
By contrast, only 11 percent of males from groups that experienced an alpha male turnover in the first five years of their lives go on to become alpha males.
The advantages that capuchins get from being reared in stable groups may help account for their success later in life, Perry said.
The study has been published in the journal Advances in the Study of Behavior.