Why do women live longer than men

Shorter life expectancy and higher mortality risk characteristic of males of many species. In the course of natural selection are not more important than the health and longevity, and the characteristics that ensure reproductive success, or, in the language of biology, fitness.

Fitness is more important than longevity

Adaptability - the ability to reproduce. If the benefits of increased adaptability outweighs the consequences of loss of life, nature makes the choice in favor of fitness. The impact of this can be clearly traced in women: pregnancy, childbirth and breastfeeding is physically exhausting and consuming energy. According to the research, the more a woman born children, the higher her body oxidative stress, which leads to accelerated aging after menopauseEvidence 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 spend a lot of energy on the reproductive efforts that affect them in their old age.

These efforts include including risky behavior and accumulation of greater body mass, namely the specific skeletal muscle, characteristic only for men (the muscles in the shoulders, back, arms). The price paid for this in terms of metabolic energy consumption is comparable to that women experience during pregnancy and lactation.

Nature has developed a special physiological mechanisms for controlling such communication between the device and the length of life. And hormones - one of the main factors responsible for this. In men, muscle mass and reproductive behavior regulates the hormone testosterone.

What makes the testosterone in the body

Testosterone promotes recruitment of muscle mass and metabolism, stimulates fat burning. In addition, he is responsible for the growth of facial hair and deepening of the voice, and may also increase libido and mood. It seems to be all that useful - but have high levels of testosterone and negative consequences.

Of course, you nicer to look at myself in the mirror when you do not have excess fatBut in the wild lack of body fat makes you more vulnerable in the event of infection or lack of food. This vulnerability is typical for many species in which a sharp rise in testosterone levels is a signal to increase reproductive effort.

For example, for severoavstraliyskih marsupial martens. The males of these animals is a sharp one-off increase in testosterone, which stimulates pairing - and significantly increases mortality due to aggression between males and exhaustion. Females marsupial martens live up to three years, and males do not always live up to a year.

Something similar is observed in birds. Ornithologists have observed that when artificially elevated testosterone males more successful rivals distilled and produce more offspring compared to individuals who did not receive additional hormonePhysiological effects on demography: a long-term experimental study of testosterone's effects on fitness. . But although their reproductive fitness of the above, they have reduced survival. Birds with artificially enhanced testosterone level gain less weight and do not always survive the mating season.

The negative effect of testosterone

The effect of testosterone on the human body is less straightforward, and it is more difficult to measure. Although it is still impossible to say for sure that men taking testosterone, live on less evidence to appear.

Thus, according to conducted in 2014 a study in elderly men taking testosterone increases the risk of non-fatal myocardial infarctionIncreased Risk of Non-Fatal Myocardial Infarction Following Testosterone Therapy Prescription in Men. . Yes, elevated levels of testosterone helps build muscle, but other organs in this age hardly carry this load.

Testosterone also affects the immune system.

Men are often more difficult to fight off infections than women because of testosterone suppresses the immune system, while the main female sex hormone, estradiol, strengthens it.

The latter, however, also increases the risk of developing an autoimmune disease - is another compromise that nature is ready to go in exchange for the benefit of estradiol for reproduction.

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

Way out

Why is the nature of all these permits?

Males mammals are willing to make expensive testosterone and risk themselves because the potential benefits of fitness for all kind of great.

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

To take care of their offspring, the father need to spend a lot of time with him, so the risky behaviors fades into the background, the level of testosterone decreases, and it may well prolong lifeLongitudinal Study of Body Mass Index in Young Males and the Transition to Fatherhood. . So to some extent the fatherhood is good for healthLongitudinal evidence that fatherhood decreases testosterone in human males. .

Of course, testosterone is still necessary for men to reproduce. And hardly a man once get rid of the related hormone issues. But whatever it was, to be a man still better than the marsupial marten.