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). They wanted to find out whether polygynous males had lower survival rates and aged faster than those of monogamous species. To do so, they collected the relevant data for 35 species of long-lived birds and mammals.
As they report this week in the Proceedings of the Royal Society, the pattern was much as they expected. 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.
The point about polygyny, according to Dr Clutton-Brock, is that if one male has exclusive access to, say, ten females, another nine males will be waiting to topple the harem master as soon as he shows the first sign of weakness. The intense competitive pressure means that individuals who succeed put all their efforts into one or two breeding seasons.
Here you go the case for monogamy! I wonder if the shorter life span of polygynous males is due to male competition as the study reasons, or keeping up with [the garga of] all the female mates :p