Ev Psych: Parental Preferences in Partners

Another "Bad Boy" - Shutterstock

Another “Bad Boy” – Shutterstock

“Evolution and Bad Boyfriends,” a New York Times piece on the struggle between parents and (most commonly) daughters over partner choice and how it may have evolved:

Whenever a pattern of human behavior is widespread, there is reason to suspect that it might have something to do with our evolutionary history. (Think of the fear of snakes, or the incest taboo.) You think your daughter’s boyfriend isn’t good enough? It may be evolution’s fault.

Now I generally argue against easy “ev psych” answers for questions of human behavior. But when you look at the commonalities across cultures around the world, you do find evidence of an ev-psych background that sets the stage for the much more complex cultural norms that have evolved. And many traditional cultures do have parents playing a significant or even primary role in mate selection for their offspring; arranged marriages and dowries were commonly used to assure a good match for a daughter, who would leave her parents’ household to join her new husband’s.

When thinking about mate choice, the natural starting point is the theory of sexual selection. This theory, which focuses not on the struggle for existence but on the competition to attract sexual partners, has been hugely successful in explaining the diverse courtship behaviors and mating patterns in the animal kingdom, from the peacock’s flamboyant tail to the chirping calls of male crickets.

Modern mathematical versions of this theory show how female mating preferences and male characteristics will evolve together. But when you try to apply the theory to humans, you hit a snag. In humans, there is an extra preference involved — that of the parents.

At first sight, it might seem surprising that parents and their children should evolve to have any conflict at all. After all, they share many of the same genes, and both have an evolutionary interest in having those genes persist through the generations. Shouldn’t the preferences of parents and their children be perfectly aligned?

Well, no — not completely. Parents each pass on half of their genes to each of their children, so from a genetic point of view, all children are equally valuable to them. It is in parents’ evolutionary interests to distribute their resources — money, support, etc. — in such a way that leads to as many surviving grandchildren as possible, regardless of which of their children provide them.

Children, by contrast, have a stronger genetic interest in their own reproduction than in that of their siblings, so each child should try to secure more than his or her fair share of parental resources. It is this conflict over parental resources that can lead to a conflict over mate choice.

In our study, we built a computer model to simulate the evolutionary process. We generated a large virtual population of males and females, the males all differing genetically in their ability to invest resources in raising children. The females had a genetically determined preference for this male quality, which meant that females with a strong preference were more likely to end up with a male who invested more.

The males and females that paired up in our model then mated and produced offspring, who inherited (with a small chance of mutation) the investing qualities and mating preferences of their parents. We ran our model over thousands of generations, observing which genetic traits thrived and which didn’t.

This is a “genetic algorithm,” the kind of computer simulation I used to write to discover behavioral tendencies among populations of stock traders. Like all simulations, it can only be suggestive because good results depend on duplicating the important features of both the simulated people and their environment; but it can reveal the underlying reason why certain traits and behaviors are preserved and strengthened over time.

…We added some new ingredients. First, we allowed a female’s parents to interfere with her choice of a male. Second, we allowed parents to distribute their resources among their children.

We found that over time, parents in our model evolved to invest more resources in daughters who chose mates with few resources. This unequal investment was in the parents’ best interests, because a daughter with an unsupportive partner would profit more from extra help than her more fortunate sisters (the principle of diminishing returns on investment). By helping their needier daughters, parents maximized their total number of surviving grandchildren.

But this unequal investment created an incentive for daughters to “exploit” their parents’ generosity by choosing a partner who was less supportive. A daughter who was less picky than her sisters would accept a less helpful partner, but since her parents picked up the slack she ended up with a similar amount of support, while sparing herself the costs of holding out for the perfect man.

As a result, the choosiness of females gradually declined over evolutionary time. To counterbalance this, the parental preference for caring sons-in-law increased. Hence the conflict.

It is only in the modern era that it became safe in the West for daughters to strike out on their own and put off marriage while gaining independence; parental control over mate selection is now much weaker than in traditional societies. And yet the evolved preferences for “bad boys” and the expectation that parents would come to a daughter’s assistance if resources were short as a result of the bad husband’s unreliability continued. And now we have added a state apparatus to channel resources to unwed mothers and enforce child support orders on deadbeat dads, further decreasing the downside risk of unwise partner choice.

More reading on this topic:

Why We Are Attracted to Bad Partners (Who Resemble a Parent)
“Why Are Great Husbands Being Abandoned?”
Evolve or Die: Survival Value of the Feminine Imperative
Perfect Soulmates or Fellow Travelers: Being Happy Depends on Perspective
Mate-Seeking: The Science of Finding Your Best Partner
“The Science of Happily Ever After” – Couples Communications


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