Women have a biological cap on their reproductive years. And from an evolutionary standpoint researchers have long wondered why human female longevity extends well past fertility. Other than humans, only short-finned 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 are females, seldom survive past 50.
Now a study of killer whales offers 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, wizened 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. [Lauren J. N. Brent et al, Ecological Knowledge, Leadership, and the Evolution of Menopause in Killer Whales]
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. Whale grandmas appear to be highly valuable, too.
—Dina Fine Maron
