November 24, 1998
Web posted at: 12:35 PM EST

By Environmental News Network staff

Divorce rates among tamarin monkeys can be as high as a third of all pairs in a given year.

(ENN) -- Most animals, even those previously believed to be staunchly monogamous, engage in extra-marital affairs, according to research published in the Nov. 21 issue of the New Scientist.

"Even creatures once considered as paragons of fidelity will indulge in a fling if the situation is right," writes Robin Dumbar, a professor of evolutionary psychology at the University of Liverpool, England.

"The animal world, it turns out, is full of examples of cuckoldry, cheating and even divorce, by supposedly lifelong mates as they try to overcome what I call the monogamists' dilemma," writes Dumbar.

Dumbar cites various examples of infidelity, including the South American marmoset and tamarin monkeys where "divorce" rates can be as high as a third of all pairs in a given year.

This situation is explained via a high rate in female mortality, resulting in an excess of males. According to Dumbar, with females in short supply, a male who cannot secure a mate of his own may become a "helper-at-the-nest" and help rear offspring that are not his own.

In turn, the father of the offspring will take advantage of the male helper's presence by going off in search of another female because he will be able to breed again sooner than if he waited for his current mate to come back into breeding condition.

The helper then mates with the female when she comes into estrus. "And the females seem indifferent to their mate's behavior: so long as they have a male to help with rearing the offspring, they don't seem to mind too much who he is," Dumbar writes.

Other reasons for infidelity cited by Dumbar include females choosing a mate who may be a good provider but not necessarily endowed with good genes. She will allow this mate most of her conceptions, as she needs a male to invest in her offspring, but keep a few reserved for better quality mates when she finds them.

Dumbar notes the research of Andre Dhondt at Cornell University who found that females often instigate divorce when new and better mating possibilities come along.

Extra-marital affairs are also used to keep a relationship strong. Playing on the emotional landscape of jealousy, a female may play one male off against another to prevent the pair-male from straying off in search of other females.

"Animals, every bit as much as humans, make choices about whom to pair with and for how long, and those decisions are influenced in large part by whether they will do better by staying with the current partner, by moving from one partner to another or by playing a more subtle kind of game," writes Dumbar in conclusion.

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