In all developed countries and most undeveloped ones, women outlive men, sometimes by a margin of 10 years. In the U.S., average life expectancy at birth is about 79 years for women and about 72 years for men.

There are many factors involved in why women live longer then men. One factor is the long standing tradition that men are meant to protect women. Men outnumber women in the military and policing agencies and the chances of a military man dying in combat are much greater than a military woman in the same situation. Women have continued to take more supportive roles behind the scenes and away from the front lines. Also, males are raised to take chances, to be daring and risk takers. This leads many to doing foolhardy stunts that end up killing them. Girls, on the other hand, are raised to be more careful and composed. This trend instills within the young females a greater need to think their options through before doing something risky while boys are more prone to spontaneously jumping into something head first and without any thought to the consequences.

Some believe that nature explains exclusively why women tend to live longer. They think that the magnetic semi loop feminine behavior which has the ability to store energetic matter and to keep its wave formation in a complete form, live longer than the energetic masculine semi loop that disperses into space. In this basic wave formation in nature, quantum, (or couple formation), people observe that the magnetic semi loop lives longer, stores energy and divides its formation - similar to women life span; and the energetic semi loop disperses its energy, its existence is shorter - similar to men life span.

Some experts assume that menopause is a major determinant of the life spans of both women and men. Women's life span depends on the balance of two forces. One is the evolutionary drive to pass on her genes; the other is the need to stay healthy enough to rear as many children as possible. Some expert says menopause draws the line between the two. It protects older women from the risks of bearing children late in life, and lets them live long enough to take care of their children and grandchildren. As for men, they believe their purpose is simply to carry genes that ensure longevity and pass them on to their daughters. Thus, female longevity becomes the force that determines the natural life span of both men and women.

One contributor to the gender difference in life span is the influence of sex hormones. The male hormone testosterone not only increases aggressive and competitive behavior in young men, it increases levels of harmful cholesterol (low-density lipoprotein), raising a male's chances of getting heart disease or stroke. On the other hand, the female hormone estrogen lowers harmful cholesterol and raises "good" cholesterol (high-density lipoprotein). Emerging evidence suggests estrogen treatment after menopause reduces the risk of dying from heart disease and stroke, as well as of dying in general.

Besides, males have long been involved in the habit of smoking. In the Victorian age through to the early twentieth century males had their studies, parlors, etc., in which to smoke away from women. So, males have been smoking longer. The trend in tobacco use has shown males to have been more into smoking and chewing then women up until the seventies.