Six days a week for 17 years, primatologists observed more than 65 female baboons in the Moremi Game Reserve, a national park in Botswana. They tracked things like the baboons' social interactions, their ranking within the group, and the survival rates of their offspring. Now, a team of researchers has looked at the data and found that the best way to predict whether a baboon would live to adulthood is to look at the strength of its mother's relationship with other females.
The offspring of females who formed strong social bonds with other females–especially their mothers and adult daughters—lived significantly longer than the offspring of mothers who formed weaker bonds with these relatives. (The strongest social bonds were shown to be between mothers and adult daughters, then sisters.)
Dorothy Cheney, a biologist at the University of Pennsylvania who worked on the study, explains why surviving into adulthood (about age 5 for baboons) is so important:

Females who raise offspring to a reproductive age are more likely see their genes pass along, so these findings demonstrate an evolutionary advantage to strong relationships with other females. In evolutionary terms, social moms are the fittest moms—at least when it comes to baboons.