WHAT’S the point of old men? We women have had our postmenopausal existence justified, in evolutionary terms, by the grandmother hypothesis. But the same cannot be said for men. The mystery is why they live long past their physical prime, with muscles turning to flab and potency waning.
In How Men Age, we have an answer. Biological anthropologist Richard Bribiescas covers some interesting uncharted territory. This is not a mere description of ageing. Instead, by considering male ageing in the light of natural selection, it aims to answer big questions including why men’s lifespans are shorter than women’s, why baldness, prostate disease and erectile dysfunction are so prevalent, and how humans as a species have benefited from men’s tendency to run to fat.
From an evolutionary perspective, nothing matters more than sex. And as far as men are concerned, nothing influences sexual power more than testosterone. It increases libido, promotes muscle growth and encourages risk-taking behaviour – all of which help attract a mate. But testosterone peaks in early adulthood, so that men are past their physical prime by the age of 30. It’s tempting to see it as all downhill from there. But with wit and insight, Bribiescas shows convincingly that’s not the case.
He points out that testosterone has a dark side – it can increase a man’s metabolic rate and suppress the immune system. In other words, there’s a trade-off, or as Bribiescas puts it: “macho makes you sick”. High levels of the hormone early in life help explain why men don’t live as long as women and why they are prone to prostate cancer later on. So waning testosterone can be seen as a positive development. It may make older men less physically competitive against younger ones, but men can produce offspring throughout their lives and, argues Bribiescas, as they age they develop new reproductive strategies to achieve this.
For a start, although they may lack raw strength, their experience and guile often make them better providers than their younger counterparts. Bribiescas has done fieldwork with the Ache people of Paraguay, and points to research showing that men’s hunting success peaks in their 40s, long after their testosterone levels peak.
What’s more, older men tend to become more nurturing. As testosterone decreases, a man’s girth increases, and the metabolic changes associated with growing adiposity promote care of offspring. Bribiescas calls this the “pudgy dad hypothesis”, and argues that it has implications for the evolution of our species as a whole.
Humans live far longer than other primates. For longevity to evolve, natural selection must favour long-lived individuals. Older women cannot reproduce, so they are out of the running. But if, throughout human history, pudgy older men have been fathering children, then they will have passed on genes associated with longevity to both daughters and sons.
Old men, therefore, could be the reason we all live so long. It would appear there is some point to them after all.
This article appeared in print under the headline “Golden oldies”