Stay with us here, because it gets very complicated. The authors assert that, evolutionarily, it is in the best interest of parents to distribute resources (money, support) to all of their children in any way that leads to as many grandchildren as possible. Those children, however, must compete with each other to get a greater amount their parents' resources.
The researchers built a computer model to simulate this process: Women were given a genetic preference for a male with an ability to invest resources in raising children. Their simulated offspring inherited both the preference for a partner with resources and the ability to provide those resources.
Then they threw a wrench in the model, allowing the parents of females to interfere with her choice of a male and distribute resources to their children. As a result, the parents invested more in daughters who chose males with little to offer, resource-wise, because it would then put them on equal footing with their better-off sisters and thus produce more babies.
And then it gets even more interesting. Females in the model evolved to be more likely to choose bad mates because it meant that they would get a disproportionate share of parental resources. But because that is clearly not in their best interests, parents also developed a stronger preference for sons-in-law that could provide more for their daughters.
Basically, parents may be evolutionarily predisposed to hate your deadbeat partner.
It's important to note that this is all theoretical. The authors acknowledge that many other motives come into play when choosing a potential partner. This paper is not suggesting that men are naturally meant to have more "resources," or that women only exist to have babies, or that daughters are money hungry; it's more or less a math equation, not a reflection of current gender politics. But just in case your parents do look less than approvingly on your partner, you can always blame evolution. (NYT)