Animals are essentially born to reproduce and die, except for three species who live long enough to experience menopause. Humans, short-finned pilot whales and killer whales (orcas) live far beyond their reproductive years. Scientists wonder why, especially since our closest ape counterparts, chimpanzees do not. Chimpanzees reach menopause around age 45 and die soon thereafter, even if in captivity. Orcas, on the other hand, reach menopause at 50 and can live past 90, much like humans.
Professor Darren Croft from the University of Exeter U.K. and fellow researcher Dr. Dan Franks from the University of York U.K. have been studying orcas in the wild. They are trying to determine whether post-reproductive female orcas increase the chances of survival of their family and of themselves.
Dr. Croft says,
Why would an individual stop having offspring so early in life?
Darwin believed that menopause was part of natural selection, so that the older females would not give birth at the same time as their offspring and compete for resource. In humans, it has been argued that better food and medical care prolonged life. The study of the orcas has eliminated this theory since orcas do not receive medical care.
Dr. Croft adds,
So studying them (orcas) in the wild could help us reveal some of the mystery of why menopause evolved.
The researchers placed vital life statistics like birth rates, odds of survival and death rates into a Darwinian calculator (a sort of “biological cost-benefit analysis”) to determine whether menopause is a benefit. They used data from the Center for Whale Research on San Juan Island. Does the presence of older females present a benefit to her family? Does this outweigh the genetic cost of not bearing any more offspring?
The researchers also made field observations. They went to the calm coastal Salish Sea, between Vancouver and Seattle. In a cove reside three pods, groups, of killer whales with a total of 84 members, as of December 13, 2015. J-Pod has 29, K-pod 19 and L-pod with 36.
The eldest member I nicknamed “Granny” (J-2). She is aptly named because she is estimated to be between 80-100 years old. She is a prime example of a post-menopausal orca.
The researched have spent hundreds of hours observing and filming the lives of these killer whales. They especially studied the behavior of the matriarchs. They found that these elders worked very hard to support their families, especially their older adult sons. Her offspring remain in her pod throughout their lives. The sons only leave briefly to mate with females from another pod (The male’s offspring live with their mothers in another pod) but return to swim at their mother’s side. Their mother would even feed them salmon. These sons were not children but 30-year old mature males. It was learned that if a mother whale dies, within a year, her son would most likely die.
Dr. Croft says,
From observations that had been collected on the whales, it appeared that the sons were dying shortly after their mothers died – they were basically called “mummy’s boys.” So we looked at the (survival) data and found that if a mother dies, the risk of death to her sons is around eightfold
The pods survival also seems dependent on the wisdom and experience of the matriarchs, During years when their staple of salmon is low, the elder females know where food is to be found, based on their past experience.
We noticed that the old females would lead from the front – they’re guiding their groups , their families, around to find food. It’s just like us. Before we had Google to ask where the shop was, if there was a drought or a famine, we would go to the elders in the community to find out where to find food and water. That kind of knowledge is accumulated in individuals.
The research is ongoing.
However, there is a side note. One whale matriarch from the Northwest group is missing because she is alone at the Seaquarium in Miami, Florida. Lolita, at age 50, is the only living whale captured from the Salish in captivity and there are calls for her release to reunite with her family in the wild.
From 1965-1975, marine park personnel hunted and captured 45 young killer whales to display in their marine parks. Over 13 orcas were killed in the process. This was from a whale population of only 100. The three existing pods are now being studied and not hunted. The older females are once again leading their families without fear.