For longevity, it's the survival of the nicest

In animals, too, strong social networks contribute to longer lives and healthier offspring - and now it seems that personality may be just as big a factor in other primates' longevity status. A study has found that female baboons that had the most stable relationships with other females weren't always the highest up in the hierarchy or those with close family around - but they were the nicest.

Scientists are increasingly seeing personality as a key factor in an animal's ability to survive, adapt and thrive in its environment. But this topic isn't an easy one to study scientifically, says primatologist Dorothy Cheney, of the University of Pennsylvania.

''Research in mammals, birds, fish and insects shows individual patterns of behaviour that can't be easily explained. But the many studies of personality are based on human traits like conscientiousness, agreeableness, or neuroticism. It isn't clear how to apply those traits to animals,'' she says.

Along with a group of scientists, including co-authors Robert Seyfarth, also at the University of Pennsylvania, and primatologist Joan Silk of Arizona State University, Professor Cheney has studied wild baboons at the Moremi Game Reserve in Botswana for almost 20 years.

Besides providing detailed observations of behaviour in several generations of baboons, the research has yielded a wealth of biological and genetic data.

In previously published research, Professor Cheney and co-workers showed that females lived longer, had lower stress hormone levels and had more surviving offspring when they had close, long-lasting relationships with other females (characterised chiefly by spending time together and grooming).

Although dominance rank was significant for male baboons - alpha male baboons may live longer than lower-ranking males - this wasn't true for the females. Nor was an abundance of family the key to longevity. Not all of the longer-lived, less-stressed females had large families.

To find out more about how female baboons forge bonds, Professor Cheney and co-authors focused on detailed records of observations of 45 female baboons from 2001 to 2007. As a personality gauge, the researchers used specific behaviours, including how often the females were alone, how often they touched other females, how often they behaved aggressively, how often they were approached by others and how often they grunted when approaching other females of various ranks. Among female baboons, grunting is a sign of good will, Professor Cheney says. Using these criteria, the researchers characterised the baboons as ''nice'', ''aloof'' or ''loner''. The team also tested the baboons for levels of stress hormones known as glucocorticoids.

The researchers took particular note of how often a female grunted at a lower-ranking female that didn't have an infant.

''Female baboons are besotted with babies - they love to look at them and touch them,'' Professor Cheney says. The researchers assumed that a female grunting at a lower-ranking animal with no baby had nothing to gain and, therefore, must just be nice.

Females who scored high on the ''nice'' meter were friendly to all females, the researchers report in the Proceedings of the National Academy of Sciences. They were approached most often by other females, were most sociable and had stable relationships.

''This is a highly innovative study,'' says anthropologist Sarah Hrdy of the University of California. ''It uses behavioural measures that are meaningful to the baboons themselves to probe the relationship between fitness and personality style.''

Professor Hrdy says the paper clarifies previous works showing that close social bonds - ''friendships, if you want to call them that'', she says - help ensure the survival of a female's offspring as well as her own longevity.

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