Scientists who analyzed decades of orca populations in the Pacific Northwest found that young orcas with grandmothers were more likely to stay alive than those without. What’s more, a calf’s risk of death rose dramatically for two years following the death of its grandmother. Because orca (also known as killer whale) societies are matriarchal, it’s likely that these older females carry with them crucial knowledge about food resources that can mean life or death for their kin.
“[A killer whale grandmother’s] greater knowledge and their leadership, especially when times are hard, are helping calves,” says senior author Dan Franks, an evolutionary ecologist at the University of York in the U.K. (Read about a mysterious new orca species.)
Ranging from polar regions to the Equator, orcas live in close-knit family groups of up 40 individuals. The predators work together to hunt a variety of prey, from fish to whales, depending on where they live. Generally, both male and female orcas stay in their natal pod throughout their entire lives, although both sexes search for mates from other pods to prevent inbreeding. Orca females stop reproducing around 40 and can live to 90, whereas males tend to live around 50 years.
Although orcas are listed as data deficient by the International Union for Conservation of Nature, populations are in decline—including those in the Pacific Northwest, which are the most studied orcas in the world. A triple whammy of exposure to toxic chemicals known as PCBs; a drop in the populations of their main prey, chinook salmon; and noise pollution from ocean vessels are all contributing factors to their demise.
That’s why this study, published December 9 in the Proceedings of the National Academy of Sciences, is a powerful piece of evidence for conservationists to protect orcas from such threats, Franks says.
“The death of a post-menopausal grandmother has an outsized impact on her family group,” he says, “which makes this an important conservation tool.”
“It’s really important work,” adds Janet Mann, an animal behaviorist at Georgetown University in Washington, D.C., who was not involved with the study. “We’re just scratching the surface of what these grandmothers are doing.”
Scientists have long been intrigued by menopause in women. A woman’s life expectancy at birth is generally longer than that of a man, yet women live for decades after they stop having children, whereas men can become fathers right up until death.
“Males don’t have menopause. They still have a few swimmers, even at the end,” says Mann.
From an evolutionary standpoint, that makes sense—a woman living for 40 years longer than she’s able to reproduce, not so much, Mann says. (Read how grandmothers also experience changes in their brain chemicals.)
Natural selection would seemingly prioritize a female’s ability to have as many surviving offspring as possible, and ceasing to reproduce long before the end of life would interf