What Do Humans Have in Common with Orcas, Narwhals, and Belugas?

Menopause is a pivotal life change that every woman will experience, so it may surprise you to learn how few other mammals go through menopause.

Until recently, scientists were only aware of menopause in five toothed whale species, though recent research suggests that at least one population of chimpanzees also experiences “the change of life.” All other female mammals appear to retain the ability to have offspring throughout their entire lives.

From an evolutionary standpoint, menopause is puzzling. In the simplest sense, if our purpose is to pass on our genes, a species with female members that live for decades when they can no longer reproduce seems to contradict that biological imperative.

One widely held explanation is that postmenopausal females, in both human and toothed whale social structures, often assist their offspring with raising their young. In other words, they take the job of grandmother very seriously.

A study by University of Exeter researchers, published this month in Nature, appears to support the so-called “grandmother hypothesis” by comparing toothed whales that go through menopause (orcas, narwhals, belugas, false killer whales, and short-finned pilot whales) with the toothed whales (including dolphins and porpoises) that do not.

The scientists noted similar reproductive lifespans across all of the toothed whale species, but those that go through menopause live an average of 40 years longer. By ending their fertile period so many years before the end of their lives, older female whales are no longer in reproductive competition with their female offspring. Thus, they can help ensure the survival of those offspring and assist them in raising their calves.

Whales, chimps, and "the change":