Why do men live less than women

Testosterone, of course

Why Men Don’t Live as Long as Women It’s the testosterone, don’t you know
Richard G. Bribiescas, Nautilus

Translated by Vyacheslav Golovanov, GeekTimes

Many years ago, when I was doing research for my doctoral dissertation on the evolutionary history of men in a remote hunter-gatherer tribe living in the forests of South America, I met a man in a badly worn baseball cap, which probably got him from missionaries. On the baseball cap was written: "There are three stages in a man's life: stallion, so-called, not a fighter" [Stud, Dud, Thud]. Really. It was somewhat sobering to see a summary of a lifetime's research work on a hat that you can buy for a few dollars at a roadside shop. But this is the elegance of an interesting science.

It is no secret that mortality as a result of accidents and risky behavior is much higher among young men, especially in late adolescence and immediately after 20. Insurance companies know this well. It is also known that men die earlier than women, regardless of their environment or lifestyle, and are often more susceptible to cancer and diseases of the cardiovascular system at an early age. Generally speaking, the risk of running into one of the most common 15 causes of death in the United States is greater for men than for women in almost all cases – and these causes are responsible for 80% of all deaths.

Obviously, the peculiarities of evolution play a role here. The only question is why. Why does natural selection dislike men? This is a very interesting academic question. But now that I'm over 50, I have to admit that the issue of aging is becoming more relevant with each new gray hair.

It turns out that shorter life expectancy and an increased risk of death in males is a phenomenon common among different species. Natural selection does not always favor the properties that are usually associated with health, energy and a long life. He prefers characteristics that lead to more successful reproduction, or, as evolutionary biologists say, to a greater fitness of the organism for reproduction. If the benefits of good fitness exceed the cost of a short life or poor health, biology will make a choice in favor of the former. In general, sex is more important than candles on the cake.

The compromise between longevity and reproduction is obvious for women: pregnancy, childbirth and breastfeeding are physically exhausting and take away energy. Studies have shown that the more a woman gives birth to children, the greater her oxidative stress, which can lead to accelerated aging after menopause [Ziomkiewicz, A., et al. Evidence for the cost of reproduction in humans: High lifetime reproductive effort is associated with greater oxidative stress in post-menopausal women. PLoS One 11, p. e0145753 (2016).]. A historical study of rural women in Poland from 2006 found a correlation between the number of children and the time allotted to women after menopause. [Jasienska et al., Daughters increase longevity of fathers, but daughters and sons equally reduce longevity of mothers. American Journal of Human Biology 18, 422-425 (2006).] And although we need more research, it seems that reproduction takes years of women's lives.

And what about men? They obviously do not suffer from pregnancy, but still spend a lot of energy – also to the detriment of their later life – to improve their chances of reproduction. These efforts are spent through risky behavior, the accumulation of more body weight, especially muscle mass, depending on gender – on the shoulders, back and arms. The metabolic costs of extra muscles are comparable to a woman's energy expenditure on pregnancy and breast-feeding, but such problems can more or less be dealt with. After all, it is reasonable to acquire in the course of evolution such physiological mechanisms that would help to cope with the shortcomings arising from the often conflicting needs of the body. Hormones play a crucial role in managing these problems. In men, testosterone regulates muscle growth and reproductive behavior. But, like everything else, you have to pay for it.

Testosterone is often described as a male sex hormone. Women also produce testosterone, but in much smaller quantities. In addition to its effect on such gender characteristics as stimulating beard growth and lowering the voice, testosterone is an important anabolic hormone that significantly affects the distribution of energy in men. It stimulates anabolism, or muscle building, and increases metabolism, the rate at which muscles burn calories. Testosterone also stimulates the burning of adipose tissue. And yes, it enhances libido and mood. So testosterone does a lot of things that can be called healthy – but this sword can be double-edged.

Males of the spotted marsupial marten experience a one-time jump
testosterone levels, leading to an increased desire for mating
and to an increased number of deaths

Burning fat will make you look better in the mirror, but in the wild, a lack of fat can lead to food shortages and infections. In many organisms, this effect manifests itself very clearly – a sharp rise in testosterone levels leads not only to an increase in reproduction, but also to problems with other physiological needs related to health. For example, the spotted marsupial marten is a medium–sized Australian marsupial. Males of the spotted marsupial marten experience a one–time jump in testosterone levels, leading to an increased desire for mating - as well as an increased number of deaths due to increased aggression and depletion of fat reserves. Their females live up to three years, and males at best – up to a year. As ecologist Jamie Heiniger says: "Their males practically fuck themselves to death" [Dunlevie, J. & Daly, N. Sex life of northern quolls: Reproduction rituals on Groote Eylandt exposed. www.abc.net (2014).]

The effect of testosterone on life expectancy and aging of people is not so obvious, and it is more difficult to assess, but given that men live less, you can imagine a similar situation described. Since it would be unethical to conduct experiments on men, increasing their testosterone to determine its effect on life expectancy, researchers have to look for hidden evidence, often in historical data. At the end of the XIX century in China and the Ottoman Empire, men from certain religious sects were subjected to complete removal of the genitals. [Wilson, J.D. & Roehrborn, C. Long-term consequences of castration in men: Lessons from the Skoptzy and the eunuchs of the Chinese and Ottoman courts. Journal of Clinical Endocrinology & Metabolism 84, 4324-4331 (1999). Eunuchs were common in the royal courts of pre-industrial Korea, as well as in boys' choirs in Europe in the XVII and XVIII centuries. [Min et al., The lifespan of Korean eunuchs. Current Biology 22, R792-793 (2012).] And although other ethnographic evidence of castration can be found, the three cases mentioned are unique in that, among other things, data on life expectancy have been preserved. The Chinese and the choir boys had no difference in life expectancy compared to normal men; in Korea, an increased life expectancy was recorded. Such are the complexities of science. Even if these studies had yielded the same results, it would still not be sufficient evidence to reach a final verdict. Life expectancy can also be influenced by other factors, from nutrition to socio-economic status, which are in no way related to the influence of testosterone.

To build a more complete picture, scientists needed to study the effect of adding testosterone to "intact" males. Ornithologists have shown that an increase in testosterone levels often increases the male's ability to organize several nests, resist competitors and produce more offspring. [Reed, W.L. et al. Physiological effects on demography: A long-term experimental study of testosterone’s effects on fitness. The American Naturalist 167, 665-681 (2006). Moreover, males whose testosterone levels were overestimated for natural reasons showed the same benefits. If testosterone is so good for reproduction, why don't all males maintain a high level of it? Again, you have to pay for everything. Male birds who had their testosterone levels increased reproduced better, but survived worse. They accumulated less fat and survived the breeding season with less success.

Moving from birds to humans, it should be noted that an increase in testosterone levels in otherwise healthy men is becoming increasingly popular and can provide answers about the trade-offs between reproduction and life expectancy. And although it is still very early to judge whether men with increased testosterone live less, the first evidence is beginning to appear. According to a 2014 study, older men taking testosterone were at risk of sudden but not fatal myocardial infarction within 90 days after the first procedure. [Finkle, W.D., et al. Increased risk of non-fatal myocardial infarction following testosterone therapy prescription in men. PLoS One 9, e85805 (2014).] High testosterone can have a positive effect on muscle growth, but other organs of older men may not be able to cope with the metabolic load. Obviously, more research is needed.

Testosterone not only affects metabolism: it is also responsible for a significant impact on the immune system during a man's life. As the evolutionary biologist from Yale, Stephen Stearns, says: "Machismo leads to diseases." Indeed, men often resist infections worse than women. There are several possible explanations for such differences. Perhaps men are more at risk of getting sick than women. Or, probably, men struggle worse with infections for chemical reasons – there is more and more evidence for this point of view. Testosterone suppresses the immune system, and estradiol, the main female steroid, stimulates it. However, the latter factor increases the risk of autoimmune disease in women – again, this is a compromise that nature is willing to make for the benefit that estradiol brings for reproduction. In wild populations of birds, reptiles and mammals, testosterone impairs the immune system and increases the severity of infections and the number of deaths. Whether this works in humans is still unknown, but it seems that data for regions with a high risk of infectious diseases confirm this. In 2005, researchers conducted work in Honduras and found that testosterone levels were lower in men infected with malaria compared to healthy individuals. And when sick men were cured, their testosterone levels increased. [Muehlenbein et al., The reproductive endocrine response to Plasmodium vivax infection in Hondurans. The American Journal of Tropical Medicine and Hygiene 73, 178-187 (2005).]

Infection is not the only type of disease that men need to worry about. Testosterone and other sex hormones are associated with an increased risk of cancer, especially prostate cancer. In populations with elevated testosterone levels, there is also an increase in the number of cases of prostate cancer. [Calistro Alvarado, L. Population differences in the testosterone levels of young men are associated with prostate cancer disparities in older men. American Journal of Human Biology 22, 449-455 (2010).] Again, sex wins over the candles on the cake.

So why do men tolerate the negative effects of testosterone? The Darwinian explanation is that the potential reproductive gain in male mammals is higher than in females. For the reproduction of males, an important limitation is the possibility of mating. Theoretically, a male mating with a hundred females can produce 100 or more offspring. It's not like that with females. The prevalence of polygamy in mammals, primates and in many human communities indicates the influence of this difference in restrictions on reproduction in men and women. Women can increase their reproductive capabilities by increasing the number of mating opportunities, but not by bearing more offspring. In fact, male mammals are willing to tolerate hormones that cost them dearly, like testosterone, invest in expensive tissue and behave risky, since the potential benefits of such a lifestyle are high.

All of this worked for a hominid that lived in the Pleistocene a couple million years ago. But does it make sense for modern men? Perhaps. Although culture has a very strong influence on people, the conditions of natural selection – variation of characteristic features and different success in reproduction – will not go away.

This does not mean that men cannot develop other reproductive strategies in the course of evolution. Despite the predisposition to risky behavior and the manifestation of expensive and life-shortening properties, men have developed an alternative form of reproductive participation in the form of paternal contribution to the fitness of offspring. In order for the paternal contribution to appear in the process of evolution, males need to be able to take care of their offspring. Risky behavior and expensive fabrics need to be pushed into the background in order to improve health and prolong life. And indeed, men, becoming fathers, tend to show a decrease in testosterone and gain weight. [Garfield, C.F. et al., Longitudinal Study of Body Mass Index in Young Males and the Transition to Fatherhood. American Journal of Men’s Health 10, NP158-NP167 (2015); Gettler et al., Longitudinal evidence that fatherhood decreases testosterone in human males. Proceedings of the National Academy of Sciences of the United States of America 108, 16194-16199 (2011).] It is possible that fatherhood is good for health.

I doubt that in men, and in general in humans, natural selection has stopped. We still have to endure a short life and poor health due to the history of evolution, but the essence of evolution is change. Man is very plastic. Probably because of this physiology, which is able to maintain our plasticity, we have developed our defining features as a result of evolution: large, expensive brains, long life, long childhood, offspring requiring care. It may also explain why there are already 7 billion of us. This is a very serious reproductive fitness. Men have developed new reproductive strategies, such as paternal contributions, which most likely influenced their evolutionary success. But that doesn't change the fact that they still need testosterone to reproduce. It is unlikely that one day it will be possible to get rid of its influence on life expectancy and health – but it is better than being a male spotted marsupial marten. Although, it's an awesome way to die.

Richard Bribiskas is a professor of anthropology, ecology, evolutionary biology, Deputy Dean for Development and Diversification at Yale University. Author of the books "How men age: what evolution has Revealed to us about Men's Health and Mortality" [How Men Age: What Evolution Reveals About Male Health and Mortality], and "Men: The History of Life and Evolution" [Men: Evolutionary and Life History].

Portal "Eternal youth" http://vechnayamolodost.ru  30.06.2017