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A recent research study concludes that during the nineteenth century polygamy hurt the evolutionary fitness of Mormon wives:

Polygamy practiced by some 19th century Mormon men had the curious effect of suppressing the overall offspring numbers of Mormon women in plural marriages, say scientists from Indiana University Bloomington and three other institutions in the March 2011 issue of Evolution and Human Behavior.

Simply put, the more sister-wives a Mormon woman had, the fewer children she was likely to produce.

“Although it’s great in terms of number of children for successful males to have harems, the data show that for every new woman added to a male’s household, the number each wife produced goes down by one child or so,” said IU Bloomington evolutionary biologist Michael Wade, whose theoretical work guided the study. “This regression is known as a ‘Bateman gradient,’ named after the geneticist who first observed a similar phenomenon in fruit flies.”

There are so many unsupported (and possibly unsupportable) assumptions in this paper that its hard to know where to begin. For instance, the researchers assume that evolutionary fitness is directly correlated to the number of children. But the relative gains that can be had by increasing the number of children can be offset by the effects of nurture on ensuring a particular child’s survival. Having more mothers around can certainly help to ensure a child doesn’t get killed before it’s their time to have children of their own. In other words, what matters is not how many total children that an individual spawns but rather how many survide to reproduce the species.

But even their assumptions about how many children would be produced are questionable. As the late Australian philosopher David Stove once noted,

Do you know of even one human being who ever had as many descendants as he or she could have had? And yet Darwinism says that every single one of us does. For there can clearly be no question of Darwinism making an exception of man, without openly contradicting itself. “Every single organic being”, or “each organic being”: this means you.

Since no woman bears as many children as is naturally possible, any claims about having more or fewer children must be based on some relative standard. So what was the basis for comparison? Mormon women who were not in a polygamous marriage.

Although I think the research is so flawed that the results are all but meaningless, let’s assume that it is true. What can we extrapolate from the conclusion? The obvious parallel would be women who take contraceptives compared to those who do not. Since the former are statistically less likely, all other things being equal, to have children than the latter, we can say that contraceptives hurt the evolutionary fitness of modern women.

Taking birth control therefore ensures that some other women’s children are likely to carry on the human race.

(Via: Stephen Windham)

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