A new book by anthropologist Richard G. Bribiescas shows how evolution continues to shape human health and mortality.
Evolutionary biology is an incredibly juicy subject. It has a complex history, a cast of crazy characters, and even a vast array of its own merchandise. And its ambitions are lofty — hell, the theory of evolution by natural selection aims to explain just how our planet became host to such an astounding diversity of life. The very thought of our mind-blowingly stupendous history is enough to bring a tear to my scientifically-minded eye.
It sometimes seems self-indulgent that we focus so intensely on the distinctions between humans and other species, as if we are fighting to prove our worldly dominance. However, these differences are incredibly important to understanding ourselves and our relationship to the world around us. Just like our social and cultural history, our evolutionary history has shaped us into the species we are today. Understanding our past is invaluable to many parts of our lives; it influences aspects of our biological, mental, and social wellbeing.
At the very least, it appears humans have decreased the power of natural selection. We have done this by creating societies that support individuals and their health and wellbeing. The slowest individual is no longer chased down by a lion, and the strongest male does not necessarily have the most children. By preventing disease, increasing education, and inventing birth control we have removed many selective pressures that would have greatly affected us in the past.
Yet we are still evolving, and fast. Our genes and phenotypes are not fixed. And understanding this is more important than it may seem. The cultural and social processes that have lessened the selective pressures acting on us previously have also dramatically changed our lifestyle and lifespan. In many countries, our populations are ageing. Most of us know this as an economic concern, but it also presents us with new biological challenges.
Many selection pressures have changed since our more primitive days. Dave Meier/Picography (CC0)
If people are living longer than ever before, can our bodies really be expected to keep up? To deal with problems like this, we need to properly understand their cause and realise that "technology does not replace the natural environment; it only adds to it".
So says Richard G. Biebescas in his new book, How Men Age: What Evolution Reveals about Male Health and Mortality. Biebescas explores the chapters in a male’s life and how these may give us clues to the past and future of ageing. The book centres around one question in particular: Why do men age faster than women?
Natural selection often results in trade-offs between increased survival or reproduction and a detrimental effect, such as ageing. In a study published earlier this year, Polish women who had more children showed higher levels of oxidative stress, a standard measure of ageing. This was one of the first studies to show physiological evidence of a trade-off between reproductive output and ageing in humans.
One major biological concern with ageing is antagonistic pleiotropy, when certain positive traits are associated with negative ones. For example, constant follicle depletion supports female reproduction early in life, but results in menopause in later years. This idea is key to the 'disposable soma' theory, which predicts that, in difficult or energy-poor environments, species will benefit by investing more in reproduction rather than maintenance and repair.
So if we invest more in reproduction than we do in maintenance in early life, there is going to be a cost later. As Bribiescas says, “we are not designed for longevity”.
Men carry around 20% more active metabolic tissue than women. This tissue takes an incredible amount of energy to create and maintain. So over time, as men’s bodies become unable to sustain the expensive tissue, it degrades.
Our changing environment in modern times has provided men with longer lives, resulting in a period of time after their physical prime where they must use other strategies to survive and increase reproduction. As men age and lose the survival advantages of their metabolic tissue, they may rely more on their experience and status to survive.
Modern men are seeing their societal roles change as they get older. Gato-gato-gato/Flickr (CC BY-NC-ND 2.0)
The addition of this second life chapter aligns with our social history, where the emergence of supportive communities provided new advantages to altruism and monogamy, and lessened the importance of physical strength or agility. Our biological changes, including complex brains, longer childhoods and long post-reproductive lives, may have moulded us to become better neighbours and parents. Certainly in the recent past, parents had to work together to successfully raise their offspring. This, of course, is ever-changing in our modern world, so perhaps we may see further changes in these traits as time goes on.
Bribiescas’ book delves beautifully into these complex ideas. He combines elements of biology and sociology to explore various theories behind male ageing. There may be a biological focus, but culture is more than acknowledged ‒ it is, in a way, exalted.
Bribiescas acknowledges the ‘checkered history’ of evolutionary biology, including the bouts of racism and misogyny coming out of social Darwinism. This is one of the book’s major strengths — by acknowledging the past and present issues surrounding evolutionary theory, Bribiescas engages readers with and without a scientific background.
The scientist in me greatly appreciated the noting of small sample sizes and poor study designs, while the creative thoroughly enjoyed his personal anecdotes involving drive-in theatres and The Walking Dead.
While a universal and often popular topic, evolution can be a very touchy subject. But avoiding controversy only further hinders our understanding. Bribiescas highlights the unfortunate idea that "evolutionary biologists are all out to prove it's all in the genes". His entire book addresses this controversy. Using relevant and personal examples, he explains that, although we are all shaped by evolutionary processes, biology alone cannot justify the actions of any individual. “Evolutionary biology is not the same as destiny," he writes.
We often consider ourselves distinct and separate from other animals, driven largely by social and cultural forces, and this attitude carries itself into how we treat evolutionary biology. We are too quick to assume that processes such as evolution by natural selection no longer apply to us. Bribiescas makes a wonderful case for considering evolutionary ideas in human health, and provides a great introduction for anyone wishing to join the conversation.
How Men Age was published last month by Princeton University Press.
Edited by Andrew Katsis and Ellie Michaelides
