female hetero- and homosexual individuals indicate that some of the aforementioned increases in brain activity are restricted to images of faces of the gender participants feel sexually attracted to. With regard to brain activation related to the perception of attractive bodies, one study with heterosexual participants suggests that activity in the nucleus accumbens and the anterior cingulate cortex increases with increasing attractiveness. The same study finds that for faces and bodies alike, the medial part of the orbitofrontal cortex responds with greater activity to both very attractive and very unattractive pictures. For both men and women, there appear to be universal criteria of attractiveness both within and across cultures and ethnic groups. When considering long-term relationships, some studies have found that men place a higher emphasis on physical attractiveness in a partner than women do. On the other hand, some studies have found few differences between men and women in terms of the weight they place on physical characteristics when they are choosing partners for short-term relationships, in particular with regard to their implicit, as opposed to explicitly articulated, preferences. Other recent studies continue to find sex differences for long-term relationships. While still valuing physical attractiveness, women tend to prioritize a man's status over his physical attractiveness, while men prioritize physical attractiveness over status. There is also one study suggesting that only men, not women, place greater priority on bodily compared to facial attractiveness when looking for a short-term as compared to a long-term partner. Some evolutionary psychologists, including David Buss, have argued that this long-term relationship difference may be a consequence of ancestral humans who selected partners based on secondary sexual characteristics, as well as general indicators of fitness which allowed for greater reproductive success as a result of higher fertility in those partners, although a male's ability to provide resources for offspring was likely signaled less by physical features. It is argued that the most prominent indicator of fertility in women is youth, while the traits in a man which enhance reproductive success are proxies for his ability to accrue resources and protect. Studies have shown that women pay greater attention to physical traits than they do directly to earning capability or potential to commit, including muscularity, fitness and masculinity of features; the latter preference was observed to vary during a woman's period, with women preferring more masculine features during the late-follicular (fertile) phase of the menstrual cycle.