Saturday, March 02, 2013

Why do women live much longer than men in modern societies?

Source: Mcgee via Wikipedia
"Comparison of male and female life expectancy at birth for countries and territories as defined in the 2011 CIA Factbook, with selected bubbles labelled. The dotted line corresponds to equal female and male life expectancy. The apparent 3D volumes of the bubbles are linearly proportional to their population, i.e. their radii are linearly proportional to the cube root of the population."

It is interesting to me that from male life expectancy of 52 to 60, female life expectancy is more or less a constant few years greater than male life expectancy. On the other hand, above 60 years male life expectancy, the difference between female and male life expectancy increases with greater overall life expectancy.

I wonder if there was an evolutionary advantage to having grandmothers live longer than grandfathers?

How has life expectancy been improved? I suggest that the first step has been in reducing child mortality, in large part by reducing the mortality from communicable diseases. Children are more vulnerable to these diseases since -- without immunization -- they are more likely to get the disease and if they get the disease are more likely to be very sick and perhaps to die.

In our rich countries we forget how great the toll of maternal mortality has been. Prior to the demographic transition (which tends to occur when child survival is increased if contraception is available) each woman could be expected to give birth to many children. Without modern medical attention during pregnancy and at birth, many women died in childbirth.

In our advanced societies most people survive childhood and maternal mortality is much reduced. Thus we see mortality at older ages. It is at these older ages that the mortality of women is lower than that of men. So perhaps we have evolved for old women to have lower mortality than men of the same age. If so, there might be some advantage in old women living longer than old men to promote the survival of their descendants. Perhaps over many generations, grandmothers have contributed more to the survival of their grandchildren than have grandfathers.

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