The ecology of the male life course.

• Marriage squeeze and increased sex ratio bias among unmarried persons: many societies have a surplus of young and middle aged males on the marriage market, and a substantial surplus of single women in old age; • Increasing extramarital fertility and the increase in family units that include step-parents as well as sibships of half siblings; • Migration, both international and domestic, that is often is sex-specific, producing biased sex ratios in the target population and the population of origin; • Violence, whether this be domestic, local or international, is often associated with the proportion of young men in the affected populations, especially if these men are without resources and female partners; • Morbidity and mortality: Males live shorter lives than females, suffer more illnesses and enjoy less social support if remaining single