Sugar, Salt, and Multiple Wives

Back in 2011 I wrote two posts (“Are people ‘naturally’ polygamous?” and "Why we think monogamy is normal") about how and why polygamy went from being socially acceptable to unacceptable in Western cultures. I noted that cross-culturally, polygamy has been practiced in 85% of societies that are most similar to those in which humans evolved, and that more than 99% of these polygamous societies have been classified as polygynous (one man with multiple wives) as opposed to polyandrous (one wife with multiple husbands). I also noted that within these polygynous societies, most marriages are actually monogamous. This is because although most men in these societies aspire to polygyny, relatively few succeed. In about three fourths of “polygynous” societies, fewer than 20% of men are actually married polygynously [1].

In this post, I'll address the issue of whether men could have evolved psychological mechanisms to strive for polygyny, even if polygynous unions were considerably rarer than monogamous ones in the evolutionary past.

Let me emphasize that this issue is not about what kind of mating system (for example monogamy, polygyny, polyandry, or promiscuity) is most "natural". As I’ve noted elsewhere (“The surprising source of our sexual morals”), human sexual nature appears to be “strategically pluralistic”, that is, both men and women are biologically adapted for a variety of sexual strategies, with the strategy they choose depending on various factors related to self and environment. The real question is: could men plausibly be adapted to deploy a polygynous strategy under certain conditions (as well as other strategies under other conditions), even if polygyny was rarer than other strategies in the past?

I was led me to address this question after coming across a critique of my 2011 posts. The critique's author suggests that if polygyny were rare in the evolutionary past, then men shouldn't have evolved adaptations to strive for it. As she asks, “if polygyny actually was rare earlier, what caused the presumed evolutionary adaptation in all men to want many wives?” I have some quibbles with her phrasing, since I don't believe that "all men" are adapted "to want many wives"; rather, as noted above, I believe that men are adapted to pursue polygyny under some conditions and other mating strategies under other conditions. However, the issue at the heart of her question—that of the relationship between how rare polygyny was, and how adapted men could be to strive for it—is very interesting.

It just so happens that a colleague and I address this issue in a recent article [2]. We point out that male polygynous motivations could be similar to motivations to consume nutrients such as fat, sugar and salt. These nutrients are essential for health (in appropriate quantities), but much more elusive in hunter-gatherer environments than in modern societies [3]. The game animals that are the main source of fat in these environments, for example, are much leaner than modern domesticated animals, and much harder to obtain because they must be hunted. Similar points can be made for ancestral sources of sugar (mainly fruit, occasionally honey) and salt (which had to be mined or obtained via foods with some salt content). As we note in the article, the elusiveness of these nutrients could actually have made people more rather than less adapted to strive for them, and the situation may be similar with regard to polygynous striving:

"The strength of an evolved desire to achieve any goal may relate positively to both the fitness value and the elusiveness of the goal in ancestral environments; when a reproductive reward is harder to achieve, greater motivation is required in order to achieve it. Thus, in theory, because fat, salt, and sugar were nutritionally valuable yet elusive in ancestral environments, people tend to express unhealthily strong appetites for these nutrients in environments in which they are abundant.

There is evidence to suggest that polygyny is relatively rare in small-scale societies not because men in these societies do not strive for it but because it is so difficult to achieve. It is difficult because usually only very high status men can attract multiple wives and support large polygynous families, and because already-married women often object to their husbands taking additional wives...

...[T]he ancestral elusiveness of polygyny could actually have made men more adapted, rather than less adapted, to strive for it. Given that polygyny was both elusive and reproductively rewarding to ancestral men, they may have evolved strong desires to achieve it” [2].

In other words, just as the past elusiveness of fat, salt, and sugar appears to have sharpened rather than dulled our evolved appetites for these substances, the past elusiveness of polygyny could have increased the extent to which human male nature is motivated to strive for it in many environments.

As always, it’s important to remember that even if such appetites do constitute evolved preferences, this doesn't mean that people are obliged or forced to indulge them. For one thing, indulging them may directly conflict with other goals that we are also adapted to seek: for example a taste for sugar may conflict with the goals of being healthy and attractive, and a desire for polygyny may conflict with the goals of maintaining a stable monogamous relationship and of avoiding social and legal sanctions.

References

1. Stewart-Williams, S., & Thomas, A. G. (2013). The ape that thought it was a peacock: Does evolutionary psychology exaggerate human sex differences? Psychological Inquiry, 24, 137-168.
2. Pound N. & Price M. E. (2013). Human sex differences: Distributions overlap but tails sometimes tell a tale. Psychological Inquiry, 24, 224–230.
3. Nesse, R. M., & Williams, G. C. (1994). Why we get sick: The new science of Darwinian medicine. New York: Vintage.

Copyright Michael E. Price 2014. All rights reserved.