Why women live longer than men

Fitness is more important than longevity

Fitness is the ability to reproduce. If the benefits of increased fitness outweigh the consequences of lost longevity, nature chooses to be fit. The effect of this can be clearly seen among women: pregnancy, childbirth and breastfeeding are physically exhausting and energy-consuming. According to research, the more children a woman has, the higher the level of oxidative stress in her body, and this leads to accelerated aging after menopause Evidence for the Cost of Reproduction in Humans: High Lifetime Reproductive Effort Is Associated with Greater Oxidative Stress in Post- Menopausal Women. …

Although men do not have to endure the hardships of pregnancy, they also expend a lot of energy on reproductive efforts, which affects them in old age.

Such efforts include, among other things, risky behavior and the accumulation of more body weight, namely, specific skeletal muscles characteristic only of men (muscles on the shoulders, back, arms). The payback for this is, in terms of metabolism, comparable to the energy expenditure women experience during pregnancy and lactation.

Nature has developed special physiological mechanisms to control this relationship between fitness and longevity. And hormones are one of the main factors responsible for this. In men, the hormone testosterone regulates muscle mass and reproductive behavior.

What does testosterone do in the body

Testosterone helps to build muscle mass and speeds up metabolism, provokes fat burning. In addition, it is responsible for the growth of facial hair and lowering of the voice, and can also increase libido and mood. It seems that all this is useful - but high testosterone levels have negative consequences.

Sure, you enjoy looking at yourself in the mirror when you don't have excess fat, but in the wild, lack of fat reserves makes you more vulnerable to infection or lack of food. This vulnerability is common in many species, in which a sharp increase in testosterone levels serves as a signal to increase reproductive effort.

For example, for the North Australian marsupial martens. In the males of these animals, there is a sharp one-time increase in testosterone, which provokes mating - and significantly increases mortality due to aggression between males and exhaustion. Females of marsupial martens live up to three years, and males do not always live up to a year.

Something similar is observed in birds. Ornithologists noticed that with artificially increased testosterone, males are more successful in driving away rivals and producing more offspring compared to individuals that did not receive an additional hormone. Physiological effects on demography: a long-term experimental study of testosterone's effects on fitness. … But although their reproductive fitness is higher, their survival rate decreases. Birds with artificially elevated testosterone levels gain less weight and may not always survive the mating season.

The negative effects of testosterone

The effect of testosterone on the human body is less straightforward and more difficult to measure. While it is not yet clear that men who take testosterone live shorter lives, evidence is emerging.

Thus, according to a 2014 study, older men taking testosterone have an increased risk of non-fatal myocardial infarction Increased Risk of Non-Fatal Myocardial Infarction Following Testosterone Therapy Prescription in Men…. Yes, elevated testosterone levels help build muscle mass, but other organs at this age have a hard time tolerating such a load.

Testosterone also affects the immune system.

It is often more difficult for men to fight infections than women because testosterone suppresses the immune system, whereas the main female sex hormone, estradiol, strengthens it.

The latter, however, also increases the risk of developing autoimmune diseases - another trade-off that nature is willing to make in exchange for the reproductive benefits of estradiol.

In addition, testosterone and other sex hormones are associated with an increased risk of cancer, especially prostate cancer. Population differences in the testosterone levels of young men are associated with prostate cancer disparities in older men. …

Way out

Why does nature allow all this?

Male mammals are willing to produce costly testosterone and risk themselves because the potential benefit from fitness for the entire species is so great.

However, this does not mean that there are no other options. Man has developed an alternative reproductive strategy - the paternal contribution to the fitness of the offspring, which is rare among other primates (and mammals in general).

To take care of his offspring, the father needs to spend a lot of time with him, so risky behavior fades into the background, testosterone levels decrease, and this, quite possibly, increases the lifespan of the Longitudinal Study of Body Mass Index in Young Males and the Transition to Fatherhood. … So, to some extent, paternity is good for health. Longitudinal evidence that fatherhood decreases testosterone in human males. …

Of course, men still need testosterone to reproduce. And it is unlikely that a person will ever get rid of the problems associated with this hormone. But be that as it may, being a man is still better than a marsupial marten.