Menopause

March 15, 2024

Hidden inside the back section of today’s local newspaper was a USA Today article on a recent study on the life cycles of different species of whales.  A paper published Wednesday in the journal Nature looked at 32 whale species, five of which undergo menopause.  The findings suggest menopause gives an evolutionary advantage to grandmother whales’ grandchildren.  This is a unique insight because very few groups of animals experience menopause.  In five species of toothed whales, orca (Orcinus orca), beluga whales (Delphinapterus leucas), narwhals (Monodon monoceros), short-finned pilot whales (Globicephala macrorhynchus), and false killer whales (Pseudorca crassidens), the findings suggest menopause evolved so grandmothers could help their daughters’ offspring, while not competing with the younger female for mates.  While whales may seem biologically distant from humans, there are important similarities.  Both are mammals, both are long-lived, and both live in family and social groups that help each other.  Humans are the only land-based animals that go through menopause, and the findings could offer clues about why humans evolved the trait.

When I looked online, I found Menopause, also known as the climacteric, is the time when menstrual periods permanently stop marking the end of reproduction.  Menopause in humans typically occurs between the ages of 45 and 55, but timing varies.  Menopause is a natural change but can occur earlier if you smoke tobacco, have surgery to remove both ovaries, or undergo some chemotherapy.  Menopause happens physiologically due to a decrease in estrogen and progesterone.  Prior to menopause, a woman’s periods become irregular, and they often experience hot flashes (shivering and night sweats) that can recur for four to five years.  The physical consequences of menopause include bone loss, increased abdominal fat, and adverse changes in a woman’s cholesterol profile and vascular function.  These changes predispose postmenopausal women to increased risks of bone loss (osteoporosis) and bone fracture, and of diabetes and cardiovascular disease.  Menopause in humans has long been a biological enigma, but the study of whales is providing scientists with a better understanding of human biology.

The researchers’ findings also support what is known as “the grandmother hypothesis”, which states menopause is evolutionarily useful.  Older women who are no longer able to have children can focus on supporting their children and grandchildren.  This means their family lines are more likely to survive, which has the same effect as having more children.  “What we showed is that species with menopause have a much longer time spent to live with their grand offspring, giving them many more opportunities for intergenerational health due to their long life,” said Samuel Ellis, an expert in human social behavior at the University of Exeter.  The live-long hypothesis suggests menopause increased total life span, but not how long a woman could have children.  That leads to a prediction that species with menopause would live longer but have the same reproductive life span as species without menopause.  This appears to be exactly what humans did.  The study does not prove the grandmother hypothesis is the reason for menopause in women, but it does lay out the evidence.

THOUGHTS:  Thankfully (for me), the whale study does not reflect human male life spans.  In Orca populations females live into their 60’s and 70’s, but males are all dead by 40.  No one knows why human females undergo menopause even though both sexes live to be approximately the same ages.  The difference may be that for humans both grandmothers and grandfathers contribute to the well-being of their children and grandchildren.  This is an evolutionary change human dads and granddads may want to reflect on.  Act for all.  Change is coming and it starts with you.