This is scientific American 62nd science. I'm Dean of Fine Merrin. Got a minute?

Women have a biological cap on the reproductive years.

And from an evolutionary standpoint, researchers have long wondered why human

female longevity extends well past fertility. Other than humans, only short-fined pilot whales

and killer whales live three or more decades after menopause, some even

reaching their 90s.

Male whales, which are far less likely to be followed by group mates than our females, seldom

survive past 50.

Now a study of killer whales offer some clues

about why evolution may have selected for such long life.

Older females have accrued what the study authors call

repositories of ecological knowledge

that can help their entire group survive. The researchers examined more than

750 hours of killer whale video. They saw that older-wise and females were the

individuals most likely to lead younger whales to salmon feeding grounds,

especially during lean times. The study is in the journal Current Biology. The work provides the first evidence

that the advantage conferred via the knowledge held by elderly female whales may be behind

the adaptation for their post fertility longevity.

In humans, an analogous explanation for post-menopausal longevity

is part of what's called the Grandmother Effect,

the constellation of attributes that make older women especially

valuable to the community.

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