Why do men live less women

Testosterone, of course

Many years ago, when I was researching a doctoral thesis on the evolutionary history of men in a remote tribe of hunter-gatherers living in the forests of South America, I met a man in a heavily worn baseball cap, which he probably inherited from missionaries. It was written on the baseball cap: “In the life of a man there are three stages: a stallion, so you are a fighter, not a fighter” [Stud, Dud, Thud]. Really. It was somewhat sobering to see the summary of the research work of all life on a hat that you can buy for a few dollars in a roadside shop. But this is the elegance of interesting science.



It is no secret that the mortality rate as a result of accidents and risky behavior is much higher among young men, especially in late adolescence and immediately after the 20th. Insurance companies know this well. It is also known that men die before women, regardless of the 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 US is greater for men than for women, in almost all cases - and these causes are responsible for 80% of all deaths.



Obviously, the features of evolution play a role here. The only question is why. Why natural selection does not like men? This is a very interesting academic question. But now, when I am already over 50, I have to admit that the issue of aging is becoming more relevant with each new gray hair.







It turns out that a shorter life span and an increased risk of death in males is a phenomenon that is common among different species. Natural selection does not always favor 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 the organism's greater adaptability to reproduction. If the benefits of good fitness exceed the price of a short life or poor health, biology will opt for the first. In general, sex is more important than candles on the cake.



The trade-off between longevity and reproduction is obvious to 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 more her oxidative stress, which can lead to accelerated aging after menopause [Ziomkiewicz, A., et al. If you are living in post-menopausal women. PLoS One 11, p. e0145753 (2016).]. A historical study of rural women in Poland in 2006 found a correlation between the number of children and the time women spent after menopause. [Jasienska, G., Nenko, I., & Jasienski, M. Daughters, Increase Longevity of Mothers. American Journal of Human Biology 18, 422-425 (2006).] And although we need more research, it seems that reproduction takes years from a woman’s life.



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 the chances of reproduction. These efforts are spent through risky behavior, the accumulation of more body mass, especially muscle mass, depending on the floor - on the shoulders, back and arms. The metabolic costs of additional muscles are comparable to a woman’s energy expenditure on pregnancy and lactation, but more or less such problems can 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 the male sex hormone. Women also produce testosterone, but in much smaller quantities. In addition to its effect on gender, such as stimulating beard growth and lowering 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 speed 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 beneficial to health - but this sword can be double-edged.





The males of the spotted marsupial marten experience a one-time jump in the level of testosterone, leading to an increased desire for mating and an increased number of deaths.



By burning fat, you will look better in a mirror, but in the wild, lack of fat can lead to a lack of food and infections. In many organisms, this effect is manifested very clearly - a sharp rise in testosterone levels leads not only to an increase in reproductive performance, but also to the appearance of problems with other physiological needs related to health. For example, the spotted marsupial marten - the average size of the Australian marsupial. Males of mackerel marmoses 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 the males at best - up to a year. As ecologist Jamie Heiniger says: “Their males practically exhaust themselves to death” [Dunlevie, J. & Daly, N. The life of the northern quolls: Reproduction rituals on Groote Eylandt exposed. www.abc.net (2014).]



The effect of testosterone on life expectancy and the 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 experiment on men, increasing testosterone to determine its effect on life expectancy, researchers have to look for hidden evidence, often in historical data. At the end of the 19th century, men in certain religious sects in China and the Ottoman Empire were completely removed from their genitals. [Wilson, JD & Roehrborn, C.Ch. Journal of Clinical Endocrinology & Metabolism 84, 4324-4331 (1999).] Eunuchs were common at the royal courts of pre-industrial Korea, as well as in the boys' choirs in Europe in the 17th and 18th centuries. [Min, KJ, Lee, CK, & Park, HN The lifespan of Korean eunuchs. Current Biology 22, R792-793 (2012).] Although it is possible to find other ethnographic evidence of castration, these three cases are unique in that, among other things, there are data on life expectancy. The Chinese and boys from the choirs had no difference in life expectancy compared with normal men; in Korea, an increased life expectancy was recorded. These are the complexities of science. Even if these studies would give the same results, it would still not be sufficient evidence for a final verdict. Other factors can affect life expectancy, from nutrition to socio-economic status, which are not 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 increasing testosterone levels often increases a male’s ability to organize several nests, confront competitors and produce more offspring. [Reed, WL, 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, the males, whose testosterone levels were overestimated for natural reasons, showed the same benefits. If testosterone is so good for reproduction, why don't all the males support its high level? Again, you have to pay for everything. The males of birds, which increased the level of testosterone, multiplied better, but survived worse. They accumulated less fat and survived the breeding season with less success.



Turning from birds to people, it should be noted that an increase in testosterone levels in healthy men by other indicators 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 less testosterone live less, the first evidence begins to appear. According to a 2014 study, aged men taking testosterone were at risk of sudden, but not fatal, myocardial infarction within 90 days after the first procedure. [Finkle, WD, 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 cope with the metabolic load. Obviously, more research is needed.



Testosterone not only affects the metabolism: it is also responsible for a significant effect on the immune system during the life of a man. As an evolutionary biologist from Yale says, Stephen Stearns: “Machism leads to diseases.” Indeed, men often resist infections worse than women. There are several possible explanations for such differences. Perhaps men are more likely to get sick than women. Or, probably, men for chemical reasons struggle with infections worse - for this point of view there is more evidence. Testosterone suppresses immunity, 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, which nature is ready to accept for the benefit that estradiol brings for reproduction. In wild populations of birds, reptiles and mammals, testosterone impairs immune function and increases the severity of infections and the number of deaths. It is still unknown whether this works in people, 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 with healthy individuals. And when sick men cured, their testosterone levels increased. [Muehlenbein, MP, Alger, J., Cogswell, F., James, M., & Krogstad, D. The Result of the Response 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 older men. American Journal of Human Biology 22, 449-455 (2010).] Again, sex wins the candles on the cake.



So why do men tolerate the negative effects of testosterone? The Darwinian explanation is that the potential reproductive gain among male mammals is higher than that of females. For the reproduction of males, mating opportunities are an important limitation. In theory, a male mating with a hundred females can produce 100 or more offspring. Females are not so. The predominance of polygamy in mammals, primates and in many human communities suggests the effect of this difference in reproduction restrictions in men and women. Females can increase their reproductive capacity by increasing the number of mating opportunities, but not by carrying more offspring. In fact, male mammals are willing to endure hormones that cost them dearly, like testosterone, invest in expensive tissue and act risky because the potential benefits of such a lifestyle are high.



It all worked for a hominid who lived in the Pleistocene a couple of million years ago. But does it make sense for modern men? Maybe. Although culture greatly influences people, the conditions of natural selection — the variation of characteristics and the different success in reproduction — will not disappear anywhere.



This does not mean that men cannot develop other reproductive strategies in the course of evolution. Despite their predisposition to risky behavior and the manifestation of costly and life-shortening properties, men developed an alternative form of reproductive participation in the form of a father's contribution to the fitness of offspring. In order for the father's contribution to appear in the process of evolution, the males need to be able to take care of their offspring. Risky behavior and costly tissues need to be relegated to second place in order to improve health and prolong life. And indeed, men, becoming fathers, tend to demonstrate a decrease in testosterone and gain weight. [Garfield, CF, et al. Males and the Transition to Fatherhood. American Journal of Men's Health 10, NP158-NP167 (2015); Gettler, LT, McDade, TW, Feranil, AB, & Kuzawa, CW. Proceedings of the United States of America 108, 16194-16199 (2011). Paternity may be good for health.



I doubt that in men, and in general in humans, natural selection 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. The man is very plastic. Probably because of such a physiology capable of maintaining our plasticity, we developed, as a result of evolution, our defining features: large, expensive brains, long life, long childhood, offspring requiring care. This may also explain why we are already 7 billion. This is a very serious reproductive fitness. Men developed new reproductive strategies, such as a paternal contribution, which most likely influenced their evolutionary success. But this does not change the fact that they still need testosterone to reproduce. It is unlikely that it will ever be possible to get rid of its effect on life expectancy and health - but this is in every way better than being a male spotted marsupial marten. Although it is a fun way to die.



Richard Bribyskas is a professor of anthropology, ecology, evolutionary biology, and deputy dean for development and diversification at Yale University. The author of the books “How Men Grow Old: What Evolution Has Discovered to Us About Men's Health and Mortality” [How Men Age: What Evolution Reveals About Male Health and Mortality], and “Men: Life History and Evolution” [Men: Evolutionary and Life History] .