Most mammals don't live long past their reproductive years, failing to serve much evolutionary purpose after they can stop passing on their genes to offspring.

Only three long-lived social mammalian species are known break that mold. Killer whales (Orcinus orca), pilot whales (Globicephala macrorhynchus) and humans (as well as possibly some other great apes) all have females that generally live for decades after they cease being able to bear young. So what might we have in common with these cetaceans?

A new study, published online June 30 in Proceedings of The Royal Society B: Biological Sciences, describes a strong link with specific social patterns that might predispose females to live beyond their fertile years.

"Whether it is younger or older individuals that are most likely to refrain from breeding and adopt the role of kin-selected helpers, depends on the pattern of dispersal and mating," the researchers concluded.

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