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.

Evolutionary biologists had built this kind of model before to understand mating preferences in other animals, but 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.

We’re not suggesting that the person you choose as a partner comes down entirely to your genes. Cultural factors, personal development and chance events presumably have a far greater influence. But given the prevalence of mate-choice conflict, it seems likely that evolution has played an important role.