Polygamy acted as husbandly insurance against an individual wife’s barrenness, as well as high child mortality rates, and made ill or aging wives less burdensome. If it was taboo to have sex with pregnant and lactating women (which increased a nursing child’s chances of survival), new fathers suffered neither sexual privation nor a waiting period to produce another child. And with so many children, polygamists had plenty of sons to work the land or contribute to their commercial ventures; in militaristic societies, these sons were prized as military recruits. Daughters, less valued, were still useful for domestic work, or to be advantageously married off to polygamous men.That's from a wonderful article on the possibility of legalizing polygamy in Canada. A concern this article raised, but didn't answer, is how the culture of polygamy, like illegal drugs, might change if it was raised out of the legal shadows.