Public Release:  Rethinking the role of affiliation and aggression in primate groups

University of Illinois at Urbana-Champaign

BOSTON, Mass. -- One of the fundamental assumptions about primates is under attack. Two American primatologists are challenging the current and dominant theory that competition is the driving force of social behavior in primates - both human and non-human.

In place of the "aggression-competition-reconciliation model" of primate sociality, the researchers offer a new theory that recognizes cooperation and affiliation as the species' primary social behaviors.

The new paradigm or model proposed by professors Paul Garber, from the University of Illinois, and Robert Sussman, from Washington University, is based on their extensive field research on primates. One of their criticisms of the dominant model, which has focused on competition and aggression to the virtual exclusion of cooperation and affiliation, concerns the database that has been used to test theories of primate sociality.

Until now, "data on the contexts and functions of affiliative, cooperative and agonistic behaviors in wild primates have been extremely limited," Garber and Sussman wrote in an abstract prepared before the AAAS meeting.

In order to illustrate the problems inherent in the dominant model, the primatologists explored "a basic question of primate sociality, namely, how much time do diurnal, group-living primates spend in social behavior, and how much of this time is affiliative and agonistic?" What they found with regard to social behavior in group-living prosimians, New and Old World monkeys and apes is that most primate species devote only 5 to 10 percent of their "activity budget" to social interactions.

Their data also indicate that rates of aggression are "extremely low, normally less than 1 percent of the activity budget." "Affiliative" behaviors, on the other hand, are 10 to 20 times more common.

The researchers explain that their new model examines the effects of group size on the costs and benefits of primate sociality, and "provides a proximate explanation of how primates live in relatively stable, peaceful groups, and solve the problems of everyday life in such a generally cooperative fashion."

Driving their research is the concern that "some authors have accepted a competition-aggression-reconciliation paradigm as a default explanation of primate social and mating systems without critically evaluating its assumptions or appropriately testing alternative hypotheses." As Garber and Sussman see it, two major theoretical problems surround that sociobiologically based model.

First, the paradigm assumes that competition is the main driving force behind both agonistic and affiliative social behavior.

"Certainly there is no question that affiliative, agonistic and competitive behaviors are a consequence of social life and present in all primate species," Garber and Sussman wrote. "However, there are reasons to believe that competition is not the main driving force of social behavior.

"Evolution proceeds at an extremely slow pace and, therefore, there is no justification to assume that we are observing dramatic evolutionary events in every population currently under study."

For example, experiments with thousands of generations of bacteria and fruit flies have demonstrated that rapid directional selection only occurs after serious environmental change; little change occurs once a population has adjusted to the environment.

"If we assume that interactions between individuals are neutral in relation to evolutionary phenomena at any particular point in time, then competition over food and mates may not be directly responsible for driving sociality. "Under this set of assumptions, the current sociobiological paradigm fails to explain the context, function and social tactics underlying affiliative and agonistic behavior.

"In other words," they wrote, "if the goal of a given behavioral interaction represents a proximate response to solve or avoid some immediate social or ecological problem, and not solely to pass on one's genes at the expense of fellow species, there must be other factors driving social behavior."

The second problem involves "an unstated assumption" of most models of primate competition, namely, that groups in the population quickly reach maximum size, and therefore the addition of even one or two new members, through births or migrations, results in significant costs in feeding competition, travel costs and increased aggression.

"If mechanisms exist such that groups in a population are maintained below maximum group size or group-carry capacity, then within group feeding, competition may not be a pervasive factor in driving primate sociality and individual reproductive success." Garber and Sussman argue that "behavioral flexibility" in primate foraging and social tactics is best explained as "a proximate decision-making response to current and changing social and ecological information." The bottom line is that "Cooperative and affiliative behaviors are considerably more common than agonistic behaviors in all primate species."

###

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.