Image: Adult male pigtailed macaque photographed in Thailand.
Frans de Waal
In a primate group where females are the dominate gender, researchers say this adult male pigtailed macaque would be among the low men on the totem pole.
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updated 7/16/2008 12:33:46 PM ET 2008-07-16T16:33:46

Among monkeys and other primates, males typically bully females around. But when males outnumber females, surprisingly females often prove the dominant sex.

These new findings could also hold true with humans, researchers said.

Monkeys live in pecking orders where the most aggressive rule, and they have to battle for their place in this hierarchy every day. As male primates are usually larger than females, it comes as no surprise they rank above females in many primate species.

However, there are times when females triumph as the dominant sex among primates — lemurs in Madagascar, for instance, or with macaques.

To help unravel the mystery of this female dominance, scientists in the Netherlands and their colleagues generated a virtual realm they dubbed Domworld. This computer model simulated fights between primates.

Unexpectedly, DomWorld predicted females would dominate in groups where males outnumbered them. Analysis of previous data regarding female dominance among many different primate species verified this prediction.

Surprisingly, females were not larger in species where they dominated. Instead, the secret to their success may be largely due to odds.

To start with, assume that a monkey wins a fight by chance. As a consequence, it grows more confident and thus goes on to win more fights.

The presence of more males in the group leads to more interactions between males and females than in groups with fewer males, "causing more chance winnings by females," explained researcher Charlotte Hemelrijk, a primatologist at the University of Groningen in the Netherlands. Buoyed by such success, "these females will go on to win more frequently in later interactions and grow more dominant."

Another way females can rise to dominance when outnumbered by males is based in how "male aggression is more intense than that of females," Hemelrijk said. "In groups with more males, males are more often defeated by other males. Consequently, high-ranking females may be victorious over these losers."

When it comes to humans, Hemelrijk speculated that it would be intriguing to see whether in discussion groups with a higher number of men whether the opinion of women is paid attention to more. "Also in fiercer cultures, we might expect more dominance of women," she told LiveScience.

Hemelrijk and her colleagues Jan Wantia and Karin Isler will detail their findings July 16 in the journal PLoS ONE.

© 2012 LiveScience.com. All rights reserved.

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