Study finds that when men outnumber women, men looking for mates have shortened lifespan than when gender balance is more equal.
? Love stinks! - the J. Geils band told the world in 1980, and while you can certainly argue whether or not this tender and ineffable spirit of affection has a downside, working hard to find it does. It may even shorten your life.
A new study by Harvard researchers shows that ratios between males and females affect human longevity. Men who reach sexual maturity in a context in which they far outnumber women live, on average, three months less than men whose
competition for a mate isn?t as stiff. The steeper the gender ratio (also
known as the operational sex ratio), the sharper the decline in lifespan.
?At first blush, a quarter of a year may not seem like much, but it is
comparable to the effects of, say, taking a daily aspirin, or engaging in
moderate exercise,? says Nicholas Christakis , senior author on the study and
professor of medicine and medical sociology at Harvard Medical School as
well as professor of sociology at Harvard University’s Faculty of Arts and
Sciences. ’A 65-year-old man is typically expected to live another 15.4
years. Removing three months from this block of time is significant.’
These results are published in the August issue of the journal Demography .
An association between gender ratios and longevity had been established
through studies of animals before, but never in humans. To search for a link
in people, Christakis collaborated with researchers Lei Jin , from the Chinese
University of Hong Kong , Felix Elwert of the University of Wisconsin , and Jeremy Freese of Northwestern University.
The researchers looked at two distinct datasets.
First, they examined information from the Wisconsin Longitudinal Study , a
long-term project involving individuals who graduated from Wisconsin high
schools in 1957. The researchers calculated the gender ratios of each
high-school graduating class, then ascertained how long the graduates went
on to live. After adjusting for a multitude of factors, they discovered
that 50 years later men from classes with an excess of boys did not live
as long as men whose classes were gender-balanced. By one measurement,
mortality for a 65-year-old who had experienced a steeper sex ratio decades
earlier as a teenager was 1.6 percent higher than one who hadn?t faced such
stiff competition for female attention.
Next, the research team compared Medicare claims data with census data for a
complete national sample of more than 7 million men throughout the United
States and arrived at similar results (for technical reasons, the study was
unable to evaluate results for women who outnumbered men at sexual
Much attention has been paid to the deleterious social effects of gender
imbalances in countries such as China and India , where selective abortion,
internal migration and other factors have in some areas resulted in men
outnumbering women by up to twenty percent. Such an environment, already
associated with a marked increase in violence and human trafficking, appears
to shorten life as well.
The researchers have not investigated mechanisms that might account for this
phenomenon, but Christakis suspects that it arises from a combination of
social and biological factors. After all, finding a mate can be stressful,
and stress as a contributor to health disorders has been well documented.
Says Christakis, ’We literally come to embody the social world around us,
and what could be more social than the dynamics of sexual competition??