Bertrand Desjardins, a researcher in the demography department of the University of Montreal, explains.

Men dying sooner than women makes sense biologically: because 105 males are born for every 100 females, it would assure that there are about the same number of men and women at reproductive ages. But even though women showed a longer life expectancy in almost every human society in the last decade of the 20th century, the size of the advantage varied greatly. For example, in the U.S. male life expectancy was 73.4 years for males and 80.1 years for females, a difference of 6.7 years, whereas in France it was 7.8 years and in the U.K., 5.3 years. The discrepancy was much greater in some countries, with the difference in Russia reaching more than 12 years, but in others, such as India (0.6 year) or Bangladesh (0.1 year), it was much less.

The diversity in worldwide longevity alone indicates that the difference in mortality between the sexes is not purely biological and that there are intervening social factors. The current range of situations actually reflects different stages of a three-part historical evolution. Women most probably have a biological advantage that allows them to live longer, but in the past--and in several places, still today--the status and life conditions of women nullified this benefit. Today, given the general progress in female life conditions, women have not only regained their biological advantage, but have gone much beyond it, both because they tend to engage in fewer behaviors that are bad for health than men do and because they better profit from current advances in health care and living conditions.

The biological advantage that women have is taken as a certainty, because the mortality of males is higher than that of females from the very outset of life: during the first year of life, in the absence of any outside influence which could differentiate mortality between the sexes, male mortality is 25 to 30 percent greater than is female mortality. The genetic advantage of females is evident. When a mutation of one of the genes of the X chromosome occurs, females have a second X to compensate, whereas all genes of the unique X chromosome of males express themselves, even if they are deleterious. More generally, the genetic difference between the sexes is associated with a better resistance to biological aging. Furthermore, female hormones and the role of women in reproduction have been linked to greater longevity. Estrogen, for example, facilitates the elimination of bad cholesterol and thus may offer some protection against heart disease; testosterone, on the other hand, has been linked to violence and risk taking. Finally, the female body has to make reserves to accommodate the needs of pregnancy and breast feeding; this ability has been associated with a greater ability to cope with overeating and eliminating excess food.

Even though many biological and genetic factors have been identified, their overall effect is impossible to measure, especially given the influence of social factors on mortality. The extraordinary economic and social progress that has occurred since the 18th century has been accompanied by a dramatic reduction of the social differences between men and women and of the burden of motherhood, which had previously negated women's biological advantage. But the recent mortality trends have gone much farther than the mere recovery of an original advantage, creating instead a new advantage of greater magnitude for women. Observations indicate that the growing excess male mortality in industrial countries could be explained by the rise of so-called "man-made diseases," which are more typically male. These include exposure to the hazards of the workplace in an industrial context, alcoholism, smoking and road accidents, which have indeed increased considerably throughout the 20th century.

But if these diseases are the only explanation for longer female life expectancy, why has the gap continued to grow even though male and female behavior and life conditions have been converging in recent years? Part of the paradox can certainly be explained by the fact that this convergence is not absolute: male smokers tend to smoke more cigarettes than female smokers do, and men drive more recklessly than females drivers, for instance.

French demographer Jacques Vallin has long been monitoring longevity in general and sex differences in mortality in particular. He adds to the above an interesting explanation of women's current mortality advantage that could explain the more recent trends: the dramatic increase in excess male mortality emerged as an equally dramatic progress in the general health conditions of our societies was taking place. He thus argues that beyond the negative behavioral or environmental factors that affect men more than they do women, there could be very well be a more fundamental difference in lifestyles that allows women to better benefit from the general progress in health. For example, although women now participate massively in the work force, their roles remain different and their professional activities are, on average, less prejudicial to their health. In addition, women often relate to their bodies, their health and their lives in general in a much different way than men do. To caricature, women seek beauty, men seek strength and power; thus, a woman's body must remain young and healthy as long as possible, whereas a man's body must be submitted to risks and challenges from an early age. The result is that women, much more than men, are attentive to their bodies and their needs and often carry on deeper dialogs more easily with their doctors. Hence, women, being more inclined to take care of their bodies and to prolong their lives, may be better able to glean greater profit from modern medical and social advances by practicing activities that are healthier and better protect their bodies. In this context, women's biological advantage now appears relatively minor in the total mortality differences between the sexes.