When it comes to baby making, polygamy really excels
I beg to differ. Polygamy excels only in making more babies for one particular man – and only up to a point – but it does not increase the fertility of society as a whole, and often hurts the fertility of individual women and families. It reduces the fertility of women (the most important element in growing a population), and it deprives other men of wives. In a population of seven men and seven women, there would be no more babies if one man married all seven women than if each man married one woman. In fact, there would be fewer, because the polygamous man’s attentions would be divided among the women, giving each less opportunity to conceive, whereas if each woman has a man to her own, she is subject of his continual attention.
What about circumstances where women outnumber men? The argument still holds in those cases, because the women would need to outnumber the men by a whole lot, so drastic is the reduction of female fertility under polygamy. Studies of nineteenth century Utah polygamy have shown that the introduction of a new wife to a Mormon household would lower the average lifetime fertility of the other wives by one child each. The result was a lower birth rate for Mormons. (Documentation
here.) This means that if a woman were likely to have four children in a monogamous union, then if her husband took a second wife, she would now be likely to have only three. And if the husband took a third wife, she could be expected to have only two. And the second wife would also be less fertile in the same way. Continuing with the assumption that the expected number of children per wife in a monogamous relationship is four, here are the numbers for the overall fertility of a polygamous family as the number of wives increases:
One wife: 4 x 1 = 4
Two wives: 3 x 2 = 6
Three wives: 2 x 3 = 6
Four wives: 1 x 4 = 4
Now I have chosen the number four just for convenience, to illustrate a principle. On this scenario, marriage to four wives produces no more children than having one, and actually yields a decrease in the population. Even if the number of likely children was higher then, say six or seven or eight, there would still be a peak number beyond which taking more wives becomes counterproductive, and at every step, an additional wife would be tragically detrimental to the others. Consider that if a man had six wives and took a seventh, the last wife would decrease the total fertility of the other women by one child per woman. That means, she would need to have six children of her own
just for the family to break even, and she would have to do this while sharing the attentions of her husband with the other women.
Let’s return to the figures in my table. Suppose that in a monogamous society, there were one other man available to marry the second wife. Already, that would produce a greater number of children total, because each couple would have four children, a total of eight, while the last two wives would have some chance to marry someone else. Again, if we stick to the assumption of four children, two men with one woman each are more fertile and one man with four women to himself. That is a 200% rate of increase for the monogamous situation (4:8) against a small decrease in the polygamous case (5:4). If the normal rate of birth were something higher, like seven, one man with three wives would have only a slight edge over two monogamous couples, fifteen to fourteen.
This shows that polygamy is not, and in the case of the Mormons was not, a means to increase seed unto the Lord, the one justification for polygamy allowed in the
Book of Mormon. (Jacob 2:30) Dare I suggest, however, that the diminishing of female fertility is an indirect offense to the chastity of women, the Lord’s love of which is the principle grounds for opposing polygamy in the same text? (Jacob 2:29) The whole beauty of sexual purity is that it reserves sexual activity for those contexts in which it is able to give rise to life through love. But a marital situation that distances a woman from her husband’s love at the further cost of diminishing her ability to give life reduces the value of sexuality simply. By implication, that lessons the value of chastity as well, since it degrades the ultimately fruitful ends to which premarital virginity is ordered.
