Popular wisdom and established evolutionary science hold that the sexes seek fundamentally different relationships: men want short-term, no-strings-attached relationships whereas women value longer-term, loyal partnerships. The explanation generally comes down to biological differences between men and women. Because women invest more in reproduction than men do β think pregnancy, morning sickness and stretchmarks β being picky becomes important because choosing poorly can be costly, even devastating.
However, for men, reproduction may only entail a brief sexual liaison and a bit of sperm β there are potentially no long-term costs.
This calculus has been built into our psychology , many argue. Think about it more carefully, though. Where do all the women sleeping with these guys come from? As theorist Hanna Kokko noted , it takes two to tango. If we go by the numbers, in a group with an equal number of both sexes, it is impossible, on average, for men to have more partners than women.
So why do we expect male psychology to be so hellbent on one-night stands? And why, clearly in opposition to this notion, are many men often so devotedly paternal? According to MMT, relationship preferences are expected to follow not simply from these fixed biological propensities, but also to be heavily influenced by partner availability. If we think of the number of men and women in market terms, namely supply and demand, the rarer sex has more bargaining power in the market place.
Individuals of the less numerous sex are more likely to get their way because they are awash with options. In theory, they can, if not pleased with a relationship, or terms therein, easily replace a disappointing partner. The more abundant sex, by contrast, has fewer outside options and must cater to the preferences of the rarer sex. For example, when there are extra women, men face a favorable market and can behave promiscuously, offering little parental investment to their mates.
