Darwin and the XY chromosome

A provocative new book by an American anthropologist about the influences of evolutionary biology on men’s health will cause both genders to think about the past and the future.

By
December 11, 2016 01:43
shirtless man

Shirtless man [illustrative]. (photo credit: INGIMAGE)

 
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Anthropologists usually investigate quaint indigenous human cultures of the present or past such as the Aleut people in Alaska, the Maasi of Africa, the New Zealand Maori or, for that matter, the ancient Hebrews in this part of the world. But few in this social sciences specialty look specifically at half of all people in the world – men.

Richard G. Bribiescas, a professor of anthropology, ecology and evolutionary biology at Yale University in Connecticut, uses an evolutionary magnifying glass to study males and how they change as they get older. His 177-page hardcover book How Men Age: What Evolution Reveals about Male Health and Mortality, just published by Princeton University Press (around $22) will captivate men – and women – interested in what makes males tick at a variety of ages. It contains a lot of scientific language to digest in the fields of genetics, endocrinology and anthropology, but it is also provocative and full of humor and personal stories, plus it has 32 pages of careful notes and an index.

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The deputy provost for faculty development and diversity at the Connecticut university is in his 50s and self-described as having something of a paunch, no children by an intentional decision with his wife and a gift for understanding and assessing research.

His most important academic work involves the evolutionary biology and endocrinology of human and comparative life histories, reproduction, aging and metabolism. He has conducted field research among the Ache people of Paraguay and populations in Japan, Venezuela, Ecuador and the US, as well as various species of non-human primates.

Bribiescas received his bachelor’s degree in anthropology and psychology from the University of California, Los Angeles, followed by a master’s degree and PhD in anthropology from Harvard University.

WHILE MUCH biomedical research has dealt with the health of older men, it did not include evolutionary biology of the type promoted by Charles Darwin. But Bribiescas is the first to investigate how evolutionary theory can improve our understanding of men’s health and well-being, how natural selection affected male aging and how older men may have contributed to the evolution of some of the very traits that make men human.

Although the author and many others firmly believe in human evolution, Bribiescas notes that according to a Gallup poll two years ago, 42% of the American public believes that evolution had no part in the emergence of humans.



“This is an astonishing and dreadful figure. Not only is evolution by natural selection a central to understanding our past, but it will surely affect our future.”

No organism, he continues, “is immune to the effects of natural selection. What does change are the agents of selection. Death, morbidity and mortality are primary agents of change. We will all be cleared out, perhaps as a species, surely as individuals. The question is how that change will unfold and how older men will be enmeshed.”

To the uninitiated, biological evolution is defined as descent with modification. According to evolution scholars at the University of California at Berkeley, this definition “encompasses small-scale evolution (changes in gene frequency in a population from one generation to the next) and large-scale evolution (the descent of different species from a common ancestor over many generations). Evolution helps us to understand the history of life.”

It is not simply a matter of change over time.

“The central idea of biological evolution is that all life on Earth shares a common ancestor, just as you and your cousins share a common grandmother. Through the process of descent with modification, the common ancestor of life on Earth gave rise to the fantastic diversity that we see documented in the fossil record and around us today.” Evolution, the California scholars continue, “means that we’re all distant cousins: humans and oak trees, hummingbirds and whales.”

In general, evolutionary processes have affected the health of all mankind. But while women have their own problems from breast and ovarian cancer and a variety of autoimmune diseases, males age less successfully and live shorter lives than females.

The author “vaguely remembers” already on page one that his father had black hair. Most of the time Bribiescas remembers him, Dad had a silver mane and moustache, “sort of a mix between Clark Gable and Cesar Romero.” Except for mild diabetes and minor back problems, he enjoyed relatively good health for most of his life. He didn’t smoke after the age of 40.

“Charles Darwin and my father both lived to the age of 73. Both married, fathered children, had their share of health issues and were outlived by their wives,” he recalled.

“While my father did not write any books, venture to the Galapagos or have the fame of Darwin, both ultimately succumbed to the effects of aging and died of heart failure... Although he was not a biologist and not very familiar with physiology, hormones or the biological bits and bobs of aging, I am certain that during his later years, he understood that he was not the man he had been when he was 20... By any measure, evolutionary or otherwise, my father was a success.”

Discussing a variety of species, including birds and primates beneath man, the author offers new ideas on aging and even what roles senior-but-still-healthy males could fill in the future. He notes that chimpanzees are not very good fathers, as they leave provision of food and care of babies to the females.

“With a few exceptions such as certain South American monkeys, most mammalian males are unlikely to earn a ‘World’s Best Dad’ coffee mug on Father’s Day.”

Yet human males, despite their macho reputations, can be excellent fathers and help mothers with raising children rather than just supporting them financially or even – in the case of homosexual fathers, into which he does not go into depth – be excellent fathers without women.

Women usually live longer than men, he said, even though couples “eat the same food, live the same sort of lives physically and pay the same attention to their health.” Nevertheless, he continues, his wife is “statistically liable to last right up to when she picks out my headstone” and beyond.

Asking why it is that animal fathers invest so little in caring for their children, he answers that one evolutionary explanation is that “caring for offspring requires knowing who your offspring are – known to anthropologists as paternal uncertainty.”

While perhaps one to 10 out of 100 people’s beliefs on who their biological father is turns out to be mistaken, animals of all kinds are usually unable to know who Dad is. Just getting married (or being in a longterm relationship with a woman) and knowing who their offspring are reduces the amount of testosterone they produce, making men less aggressive and even safer drivers, Bribiescas notes.

Too much testosterone and other hormones can trigger shrinking muscles, prostate swelling and cancer, more body fat, erectile dysfunction, hair loss and shorter life expectancies than in women. In fact, if you’ve reached 30, your male hormone levels have already hit their peak, but men are not doomed to failure as a result of this decline.

All these negative effects of male hormones may even have caused positive distinguishing features to come out in men such as high rates of fertility, positive parenting and improved longevity.

He points out that the effects of testosterone involve a matter of averages. There are still fathers who abandon their children, get drunk and beat them or even murder them. Evolutionary theory, he continues, suggests that in environments with lots of hazards and a low probability of living a long life, caring for offspring may take a backseat to more risky reproductive strategies such as seeking out additional mates instead of investing in family.

The author cites actors Robert De Niro and Rod Stewart as siring children when they were in their seventh decade. Having lower levels of testosterone can make older men have more fat, which is not necessary less attractive to females. Pudgy older fathers live longer, are more attractive to the opposite sex and are better at passing on their genes than their leaner counterparts, Bribiescas maintains. But at the same time, less testosterone makes it harder for males to fight off infections and various illness compared to females. In addition, women go to the doctor and undergo lab tests more than women, who generally take better care of themselves.

Bribiescas works hard to explain why women go into menopause around their sixth decade, while men remain fertile even until death in senescence.

Women commonly have a lifespan that extends decades beyond menopause. It has been suggested that women are unable to reproduce in middle age to increase their ability to survive and raise their children to adulthood. Being fertile for many more years but then dying after menopause would not make sense. “Menopause is a physiological constraint that emergences from the biochemical limitations of ova viability.”

But the most commonly cited evolutionary explanation for menopause, he continues, is the “Grandmother Hypothesis,” in which women are “allowed” to live decades after their menstrual period ends so they have time to help their daughters take care of their children, allowing them to have even more.

Bribiescas argues that older men have not only been affected by evolution up to now, but through natural selection, they are also “likely to play a major role in shaping our evolutionary future. Looking at the history of other organisms, we can draw some conservative predictions about the future of Homo sapiens.”

Until recent centuries, bad eyesight used to be almost inevitable in the elderly, affecting their ability to hunt, forage, work and generally cope with the daily needs of life, the anthropologist continues.

“Those with terrible eyesight, like me, would have been at a distinct disadvantage compared to those who could see clearly.” Eyeglasses, however, have factored into the future of the species… Technology and new tools will continue to play an important role in our evolution.”

He points out that family planning also has the potential to change natural selection in humans.

“Since older men tend to hold the reins of economic and political power in most societies, their role in controlling resources, including emerging technologies and shaping human fertility and mortality in a non-random fashion is all but certain. In other words, whatever evolution has in store for us, older men almost surely will have a major influence,” especially as they control conflict and warfare around the world. Bribiescas argues that given man’s aggressiveness over the millennia, it would be advisable to “amplify the role of women in positions of leadership and influence.”

Concluding his thoughts about his father, Darwin and chimpanzees, the author writes that “they all shared the commonality of aging as a male and were the culmination of millions of years of evolution… Their reproduction likely accelerated their aging, hormones changed over time and caused them to get rounder around the middle, and more than a few hairs turned gray. But that’s OK. Natural selection does not form flawless organisms. It tinkers and muddles through with what was handed down from previous generations.”

Considering all that has happened, he writes that humans and older men in general have done “pretty well and have a tremendous capacity to make the world better.”

While evolutionary biology and longer lives have awarded men with problematic health issues, older males have helped “make the human condition a bit more tolerable and maybe even improved it, such as the emergency of fathers caring for children, pudgy bellies for cats and grandchildren to snooze on and perhaps a few more years for everyone to enjoy the wonderful absurdity of life,” he muses.


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