Side Note to our Polygyny Debate:

The Economist has an article this week about the inter-relation between lifespan and monogamy. Apparently there is new scientific research to suggest that male members of monogamous species outlive their male counterparts from polygynous species. Adds an interesting dimension to our earlier debate about the causes behind human societies' universal condemnation of polygamy! Here are excerpts:

In the cause of equal rights, feminists have had much to complain about. But one striking piece of inequality has been conveniently overlooked: lifespan. In this area, women have the upper hand. All round the world, they live longer than men. Why they should do so is not immediately obvious. But the same is true in many other species. From lions to antelope and from sea lions to deer, males, for some reason, simply can't go the distance.

One theory is that males must compete for female attention. That means evolution is busy selecting for antlers, aggression and alloy wheels in males, at the expense of longevity. Females are not subject to such pressures. If this theory is correct, the effect will be especially noticeable in those species where males compete for the attention of lots of females. Conversely, it will be reduced or absent where they do not.

To test that idea, Tim Clutton-Brock of Cambridge University and Kavita Isvaran of the Indian Institute of Science in Bengalooru decided to compare monogamous and polygynous species (in the latter, a male monopolises a number of females).

In 16 of the 19 polygynous species in their sample, males of all ages were much more likely to die during any given period than were females. Furthermore, the older they got, the bigger the mortality gap became. In other words, they aged faster. Males from monogamous species did not show these patterns.

Most students of ageing agree that an animal's maximum lifespan is set by how long it can reasonably expect to escape predation, disease, accident and damaging aggression by others of its kind. If it will be killed quickly anyway, there is not much reason for evolution to divert scarce resources into keeping the machine in tip-top condition. Those resources should, instead, be devoted to reproduction. And the more threatening the outside world is, the shorter the maximum lifespan should be.

There is no reason why that logic should not work between the sexes as well as between species. And this is what Dr Clutton-Brock and Dr Isvaran seem to have found. The test is to identify a species that has made its environment so safe that most of its members die of old age, and see if the difference continues to exist. Fortunately, there is such a species: man.

Dr Clutton-Brock reckons that the sex difference in both human rates of ageing and in the usual age of death is an indicator that polygyny was the rule in humanity's evolutionary past—as it still is, in some places. That may not please some feminists, but it could be the price women have paid for outliving their menfolk.

--excerpted from "Live fast, love hard, die young," The Economist, Oct 18th 2007 ed.