Men could be genetically attracted to easy sex, according to the findings of a recent study based in evolutionary theory.

Researcher Cari Goetz of the University of Texas used photographs of women looking vulnerable in different ways (called cues) which she then showed to 76 males students, asking them whether they considered the women in the photographs as sexy.

Goetz included 22 cues that indicated vulnerability, which included women who appeared sleepy or drunk, and found that 19 of these correlated with sexual attraction for the men.

Looking to evolutionary theory for an explanation, Goetz and her team believe that the male sex drive is programmed to be opportunistic. In evolutionary terms, this means that men choose women that appear more likely to give into their advances.

Given that a male produces around 85 million sperm cells on a daily basis, she believes that men are programmed to be less concerned about casual sex. On the other hand, women are generally more concerned about the consequences of sex and therefore are a little more cautious when it comes to one night stands and casual sex.

To begin with, Goetz asked the students to identify physical cues that they felt suggested a woman was potentially available. Amongst 88 of these were gestures such as licking or biting their lips, touching their breast, wearing sexy clothing, looking drunk, attention-seeking and appearing unintelligent.  

Once they had these cues from the students, the researchers found pictures that represented these 88 gestures. They asked the students to look at each picture and give a rating for how easy they thought it would be to exploit the subject using anything from a pick-up line to physical force. They also asked the men to state whether they would consider the women suitable for long or short-term relationships.

Pictures of women looking childish, drunk or sleepy were rated as the most likely to be sexually exploitable and more attractive than those women who appeared intelligent and alert. However, men also rated them as only suitable for short-term relationships.

When asked to rate these women on their suitability as girlfriends or wives, the men changed their opinion, saying they weren't at all suitable long-term partners.   

Further investigation conducted by David Lewis found that men who were less empathetic and who led more promiscuous sexual lives were most likely to take advantage of women in compromised positions.