Sociable mums make much better mothers than less gregarious ones, suggests a new study of baboons.
Baby baboons born to outgoing mums who enjoy hanging out with other females are considerably more likely to survive their crucial first year than infants born to less friendly mothers, reveals the behavioural study.
Primates and monkeys are unique among animals in the intense social bonds they form. These bonds are thought to have been crucial in the evolution of primates, including humans. Behavioural ecologists have assumed that extrovert behaviour in primates boosts survival by generally making group life easier.
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But now US biologists have shown for the first time a direct link between having friends and reproductive survival. 鈥淲hat they have been able to show here is that there are real impacts on the lifetime reproductive output of females,鈥� says Robin Dunbar, an evolutionary psychologist at the University of Liverpool, UK.
Susan Alberts, at Duke University in North Carolina, and one of the research team was surprised by the significance of sociability. 鈥淓ight per cent of infant survival is explained by sociality,鈥� she told 快猫短视频. That is 鈥渟triking鈥�, she explains, because 鈥渨e wouldn鈥檛 expect to have a large amount of variation that is deterministic 鈥� things that a mother can actually control 鈥� it鈥檚 amazing.鈥�
Long view
The team analysed data on wild baboons (Papio cynocephalus) living at the foot of Mount Kilimanjaro in Kenya. These baboons are highly sociable and live in large mixed sex groups. Females live in the area they were born forming matrilineal hierarchies, while males leave when the mature.
The researchers amassed 34,000 observations of 108 females over 16 years. They then compared the behavioural data from the observations to records of births and deaths.
Babies born to friendly mums, who enjoyed grooming and lazing around close to their buddies, were much more likely to make it to their first birthday than those born to loner mums. If a baboon survives to one year, the equivalent of a human five-year-old, it has a strong chance of making it to adulthood and breeding.
Alberts says that, in a good year, the average infant mortality rate at one year old would be about 10 per cent. In a bad year, as many as 35 per cent of baboon babies might die.
鈥淏ut the actual numbers for each female varies a lot,鈥� she explains. 鈥淢ore sociable females bring it down. The less sociable ones may not be able to cope in a bad year, and for them it may even be higher than 35 per cent.鈥�
Stress buster
Friendliness may boost infant survival by helping to combat stress in the baboon mums. Grooming is extremely relaxing for primates, slowing their heart rates and sending them to sleep. It can even induce the release of pleasurable endorphins.
It may also give 鈥渄irect material benefits鈥� says the team. For example, females clubbing together may provide offspring with protection from harassment and better access to food and shelter.
Dunbar and Alberts both agree the findings have relevance for humans. Previous studies have shown that the size of social networks among human parents influences the health and mortality of their children, says Dunbar.
鈥淲e are primates, and we are really sociable primates,鈥� says Alberts. 鈥淗umans who are more socially isolated have worse health. So nourish your social connections 鈥� nurture your friendships.鈥�
Journal reference: Science (vol 302, p 1231)
