Ever wondered why females tend to outlive males? Is gender a ‘short-cut' - a proxy to behavioural differences? Eli Friedwald takes a tour of the competing theories trying to explain the difference in life expectancy between the sexes
In contrast, male testosterone has been linked to the elevation of blood pressure and to increases in cholesterol levels – both risk factors for cardiovascular disease.
Testosterone is also a driver to greater male aggression and risk-taking, which lead to higher mortality from violence and dangerous habits.
There are also behavioural theories for gender differences. Females tend to display less harmful behaviours than males.
Typically, males indulge in more drinking, smoking and drug taking. They drive more, are more aggressive and have more stressful occupations.
Males also are less likely to consult doctors and to follow medical opinion faithfully.
In truth, the situation is not quite so ‘black and white’.
Experiments with apes have shown that male apes are more likely to get drunk than female apes when provided with the opportunity.
This suggests that some behavioural differences between the genders are strongly influenced by biology and are not a matter of simple choice or culture.
Behavioural and biological mortality drivers are fairly entangled.
Thus far, we can only conclude that there are many good biological and behavioural reasons for male mortality to be heavier than female mortality. But what does the data show?
Comparisons of male to female mortality rates can be made across many dimensions.
The analyses shown below cover time, territory, age, species and cause of death.
First the gender difference over time. Chart 1 shows the difference in life expectancy at birth between females and males in Sweden (for which reliable records go furthest back) from 1751 to the present day.
It reveals that the long-term average is in the range 2.5 to four years, with a peak of more than six years being reached in the late 1970s, declining since then to a little more than four years today.
Next, current gender differences over territories. Chart 2 shows how different territories compare, in terms of the difference between female and male life expectancy at birth, over a recent period (2004-06).
It shows that France and Japan display the largest gap (at about seven years), while the UK and Sweden has the smallest gap (4.3 years).
Focusing on the UK, chart 2 shows a recent gap in life expectancy at birth of 4.3 years.
Chart 3 displays the proportional contribution to this gap, for each year of age. As this proportion is nearly always positive, it indicates that a female mortality advantage is enjoyed at nearly every age.
This female mortality advantage is enjoyed by nearly every species of animal, ranging from mammals to nematodes (roundworms).
One exception is birds, where some sub-species do show a male mortality advantage.
Interestingly, while most species share chromosomal similarities with humans, birds do not.
