Why Male Baboons Profit From Feminine Associates

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Why Male Baboons Benefit From Female Friends

Baboons live their daily dramas in the shadow of Kilimanjaro. They quarrel, they mate, they take care of their young. Some are loners and some have lots of friends.

Now research has shown that these platonic relationships might be just as important as the relationships that make up more baby monkeys. Male baboons live longer when they have more female friends.

The findings, published last week in Royal Society B's Philosophical Transactions, come from one of the world's longest-running studies of wild primates. Researchers have been continuously observing savanna baboons in the Kenyan Amboseli basin since 1971. They have compiled a data set that includes the births and deaths of hundreds of animals, as well as the daily activities of baboons. One activity, grooming, is the foundation of baboons' social relationships.

"The really interesting behavior of nursing," in part because it's not always reciprocated, said Fernando Campos, a biological anthropologist at the University of Texas at San Antonio and a lead author. Sometimes baboons take turns combing each other's fur for insects and debris. At other times, a baboon may foster a higher-ranking baboon that does not return the favor.

Although men and women can groom one another, there is not much masculine grooming or bonding in the Amboseli population. Couples of female baboons, on the other hand, form "lifelong bonds," said Dr. Campos, and previous research, has shown that female baboons with strong relationships live longer than socially isolated women.

But what about male baboons? This question was more difficult to investigate because men join a new social group about every few years. If a male baboon disappears from the Amboseli study population, scientists have no way of knowing whether he died or joined a group further away. That makes it difficult to know how long men live.

In the new article, biologists and statisticians have worked together on a model that addresses this problem. Her data set included 542 adult baboons, both male and female, that had been observed for more than three decades. Based on the occasional death or movement people actually witnessed and the age of the male baboons when these events occurred, scientists were able to calculate the likelihood that another disappeared male had either died or migrated.

Just like with female baboons, they saw that men with more social ties – those platonic foster relationships with women – lived longer.

The same pattern has occurred in other social animals ranging from horses to dolphins. Friendships are also associated with longer lives in humans. However, it is not clear why.

"We don't really understand the actual mechanisms that turn friendships into lifespans," said Dr. Campos.

Baboons of either sex can achieve health benefits simply by having their parasites picked up. Friendships could also help animals avoid conflict. Studies in other primates have shown that social relationships reduce physiological signs of stress.

It's also possible, says Dr. Campos that causality goes the other way. Perhaps healthier animals – baboons or humans – have more energy to invest in relationships.

Oliver Schülke, a behavioral ecologist at the University of Göttingen in Germany who was not involved in the research, said it was "notoriously difficult" to study the lifespan of males such as baboons leaving the groups they were born in, one possibility Estimating this lifespan "makes a difficult subject more tangible."

Dr. Schülke added that it would be important to find out why a woman's friendship – who is not a partner and cannot help in fights because she is much smaller – could help a man live longer. He also wonders if low-ranking men invest more in such relationships because they don't spend as much energy on procreation as high-ranking men.

These top males have tough lives. Male baboons vigorously compete for the highest position within a group, which allows them to mate with many females and have many offspring. In the struggle for this position, men can injure and even kill one another. Dr. Campos and his co-authors found that high-ranking male baboons had shorter lives in Amboseli.

If a male baboon loses the top spot and survives, Dr. Campos, he often stays in the group for a while, especially when he has girlfriends there. Researchers had speculated that this might serve to protect the displaced man's boys, said Dr. Campos. However, the new study suggests that the clinging might be good for the male baboon himself: "Perhaps just seeking companionship has its own benefit."

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