How human sexual selection evolved over time is becoming clearer with new findings from the University of Colorado at Boulder showing that women in their fertile phase are more likely to fantasize about masculine-looking men and that a man's intelligence has no effect on a female's choice of partner. The researchers say this lack of an observed "fertility effect" related to intelligence is puzzling.
The findings come from a study published in the journal Evolution and Human Behavior. The study was conducted by Steven Gangestad and Randy Thornhill of the University of New Mexico and Christine Garver-Apgar, of the University of Colorado at Boulder. Other studies have shown that women's interest in men with masculine features peaks during ovulation but this is the first to confirm that the effect occurs in real couples.
The researchers define a "masculine face" as having a relatively pronounced chin, strong jaw, narrow eyes and a well-defined brow. George Clooney fits this bill, they suggest, while a less-masculine face, would include a less-pronounced jaw and wider eyes, akin to Pee-wee Herman.
Interestingly, this does not mean that "pretty boys" are less attractive as life partners. "When they rate men's sexiness, in a sense, that's when [women] show the shift," Gangestad said. "If they rate men's attractiveness as a long-term partner, then they don't show it."
The prevailing wisdom during much of the last half-century was that women did not experience estrus, the period in which other primates signal their fertility with swollen genitals. But newer research suggests that women may not have lost all remnants of estrus.
Biologists have documented that women are choosy when fertile, and their freedom to choose mates is increased because their fertile phase is not advertised as it is in other primates. A growing body of evidence suggests that, when most fertile, women gravitate toward males who show signs of good genetic quality.
Masculine facial features suggest that a man is of good genetic quality, because he had the resources during development not only to survive but also to expend energy on a macho visage. Rugged-looking jaws and eyebrows are signals of testosterone.
Instead of using his energy on other features or to maintain his immune system, the masculine-looking male may have had a "surplus energy budget," Garver-Apgar explains.
While it is not surprising that women's gazes would fall on masculine-looking men when they are most fertile, Garver-Apgar says the lack of a similar effect with intelligence is perplexing. "That we didn't find any effect of men's intelligence on their partners' sexual interests across the cycle is important because some evidence suggests that intelligence associates with genetic quality."
If intelligence correlates with good genetic quality, Garver-Apgar wonders, why is it that intelligence is not among those traits that women prefer mid-cycle? "Why don't you see a fertility effect?" she muses.
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