A new study has found that the rise of 'hookups', or sex without commitment, could be having an unexpected impact, particularly on the way women assess men's bodies.
This new research, on the kind of ideal body men and women prefer in romantic heterosexual partners, also reveals surprising differences between what men and women are looking for in each other.
The study, from Kenyon College in the USA, examined body ideals that heterosexual college women and men choose for romantic partners, by comparing responses to body silhouettes that vary in thinness, shape, and in women's breast and men's chest size.
Evolutionary theory predicts that what we are attracted to in the opposite sex is in some way genetically programmed in our brains.
Perhaps certain preferences had some kind of survival value in the ancestral environments we evolved to survive in. For example, women might seek muscular men for 'short-term mating' because muscularity is linked with dominance, and dominant men might help protect women in dangerous environments.
Previous research has found that women rated their ideal body as significantly thinner than what men selected as most attractive, and this might be because of the pervasive media representation of unrealistically thin women as attractive.
The authors of this latest study, published in the academic journal 'Body Image', conclude that from their results, it is difficult to say which gender was more critical in their assessment of the body of a romantic partner.
Women chose a body ideal for men larger, or more muscular, than men's actual bodies. In contrast, men chose a body ideal for women quite close to women's actual body size.
Women's ideal for men's chest size was significantly larger than men's actual chest size, but women's ideal for men's chest size was smaller than the ideal men had for themselves.
The study found that w omen's ideal for men's thinness was slightly smaller than the ideal men had for themselves.
The ideal that men had for a woman partner for breast size was slightly larger than women's actual rating, and it was significantly larger than the ideal that women had for themselves.
The ideal that men had for the thinness of a woman partner was not significantly different from women's actual rated thinness, yet women's ideal for themselves was significantly smaller than men's ideal for women.
Also the importance that men placed on the thinness of women was less than the importance that women placed on thinness for themselves.
Viewing more sports on television seemed to predict which men rated as more important female body ideals and the size of breasts, followed by watching more reality television.
But the more men were interested in 'hookups', and the more sexually permissive their peer culture, the thinner the ideal woman that was chosen.
So another factor, according to the authors, Sarah Murnen, Katherine Poinsatte, Karen Huntsman, Jesse Goldfar and Daniel Glaser, is that recently, "hookups," or brief sexual encounters outside the context of a committed romantic relationship, have almost become the norm among college students.
'Hookups' appear to have overtaken committed relationships in popularity and priority amongst those of college age. But because 'hookups' emphasize the physical rather than emotional, young adults who participate in 'hookup' culture might be more likely to select partners based on physical features of attractiveness.
For women, 'adversarial sexual attitudes' emerged as the most important predictor of women rating body ideals as important for a male partner.
'Adversarial Sexual Beliefs' are beliefs that heterosexual relationships between women and men are adversarial due to being opposite to one another. Those who subscribe to adversarial sexual beliefs endorse views such as "Men and women cannot really be friends" and "Men are out for only one thing". They believe that men and women are out to "use" each other, and may be more likely to invest in body ideals that magnify the differences between women and men, a thin body for women and muscular body for men.
The study, contends that women who participate in 'hookup' culture (who also have more adversarial attitudes about relationships), are more willing to judge men's bodies because they are part of a culture in which their own bodies are being judged.
Perhaps judging men by their bodies is considered "fair play." Preferring 'hookup' culture to dating was also related to the importance of the chest ideal silhouettes as rated by women.
Although women generally placed less importance on the ratings they chose for an intimate partner's body, if they believed that men and women are adversaries in romantic relationships, they were more likely to do so.
So, the rise of 'Hookup' culture might lead women to objectify men's bodies in ways similar to what men already do with women's bodies.
The problem is that body dissatisfaction rates among both women and men are increasing in recent times.
The authors of the study, entitled 'Body ideals for heterosexual romantic partners: Gender and sociocultural influences', point out that unrealistic, yet influential, images people are exposed to in the media means that recently the ideal image of women has become unrealistically thin, while the ideal image of men has become unrealistically muscular.
Perhaps we should encourage young people to try to value their bodies for what they can do, rather than what they look like.