Among human beings, it is women who have tended to be considered more attractive when rated by both men and women, and female appearance receives more attention than male appearance, even across cultures. Indeed, it is much easier to find examples of the adoration of feminine rather than masculine beauty within literary record. As Jean-Antoine Petit-Senn put it: ‘There is no beauty on earth which exceeds the natural loveliness of woman.’ So too within the arts: depictions of idealised feminine beauty far outweigh those depicting the ideal man.What for the art historian John Berger (1977) was an unfair emphasis on women’s attractiveness as a result of men’s dominance in most societies—what he termed the ‘male gaze’—is for evolutionary psychologists a natural result of evolutionary history. Competition among women for high-quality reproductive potential. Among the attributes that some evolutionary psychologists argue signal the reproductive capacity of a woman is her breasts.At first glance, female breasts would seem to be a primary candidate of a sexually selected signal in humans. Permanently large breasts are an evolutionary novelty in primates, and in human breasts are perceived as an important component of sexual attractiveness, at least in some cultures. This is underscored by the willingness of women to undergo breast augmentation surgery in order to enhance their physical attractiveness. Of course, women may choose breast augmentation surgery for different reasons (aesthetic purposes, relieve physical discomfort, and so on), but the comparable frequencies of both augmentations and reductions suggest that, as far as breasts are concerned, both smallness and largeness may be experienced as undesirable or unattractive.There appears, however, to be little evidence to suggest that breast size is associate with fertility, lactational output or health, which would seem to rule out a ‘good genes’ explanation for why men find female breasts attractive. An alternative explanation is that female breasts evolved under runaway selection as a sign of nulliparousity in women. Because breasts develop most intensely at the beginning of the reproductive age, some researchers have suggested that breasts evolved as a sexual signal of reproductive value rather than fecundity as such. In short, because breasts are a signal of reproductive age, men should have evolved mechanisms eliciting preferences accordingly. In particular, men should find large breasts more attractive than small breasts because this is a larger signal of reproductive value.  However, when psychologists have included breast size as a variable in their studies of physical attractiveness, they have generally not found consistent preferences. For instance, it was reported by Kleinke and Staneski (1980) that medium breasts evoked the most favourable ratings from participants of both sexes, when written stimuli were used. In another study, using colour photographs, the same experimenters found that women with smaller breasts were rated as competent, ambitious, intelligent, moral and modest. Women with large breasts were judged to have the opposite characteristics by both female and male participants. On the other hand, using silhouettes of the female figure that varied in breast size, Furnham and Swami (2007) found that participants rated small breast size as the most physically attractive.Gitter et al. (1983) also conducted a study with male and female participants, but in contrast to the above findings their results suggested that men preferred large breasts whereas smaller breasts were rated more favourably by women. Yet, large breasts on overweight women are not considered especially attractive.Clearly, existing studies do not present a conclusive picture of what is considered an attractive breast size in women. Related evidence that breast size preferences are highly variable was documented by Mazur (1986), who showed that ‘ideal’ breast size grew continually from its flat period in the 1920s to the large-breasted ideal of the early 1960s. Since then, in tandem with a societal idealisation of extreme thinness, preferred breast size has become smaller, although there has been a recent trend towards large-breasted figures in media appealing to men. Certainly, size is only one of several characteristics that can affect preferences to upper body shape, but it is the most public variable and principle way in which women’s breasts have come to be embodied in popular culture.Recent studies have suggested that breast size may be the least important characteristics in men’s ratings of women’s physical attractiveness, after body weight and shape. On the other hand, it is unclear whether such variability in preferences remains true when cross-cultural samples are included, although there is every reason to believe this is the case. In short, then, breast size does not appear to be a reliable predictor of physical attractiveness, despite being a good candidate for having evolved by sexual selection.