The nubility hypothesis

Abstract

A new hypothesis is proposed to explain the perennially enlarged breasts of human females. The nubility hypothesis proposes that hominid females evolved protruding breasts because the size and shape of breasts function as an honest signal of residual reproductive value. Hominid females with greater residual reproductive value were preferred by males once reliable cues to ovulation were lost and long-term bonding evolved. This adaptation was favored because female-female competition for investing males increased once hominid males began to provide valuable resources.

Resource Security Impacts Men’s Female Breast Size Preferences

“…If this were the case, then larger breast size should be no more important than fat stored in any other part of a woman’s body [17]. Rather, breast size may also act as a cue of nulliparity, age, sexual maturity, or fertility [14]–[17] and, furthermore, there may be other more important cues of fat storage compared to the breasts, such as overall body size [57], [59].…”

“…If this were the case, then larger breast size should be no more important than fat stored in any other part of a woman’s body [17]. Rather, breast size may also act as a cue of nulliparity, age, sexual maturity, or fertility [14]–[17] and, furthermore, there may be other more important cues of fat storage compared to the breasts, such as overall body size [57], [59]. This may help to explain the small-to-moderate effect sizes uncovered in both studies reported here: all things being equal breast size may indicate fat reserves, but in reality breast size is likely correlated with body mass [72], which may act as a more reliable indicator of such reserves.…”

“…More broadly, it is also possible that larger breasts size signals greater physical maturity, a trait that may be preferred under conditions of environmental insecurity. For example, it has been proposed that men may use breast size to gauge the age of a woman [17], with larger, non-sagging breasts signalling that a woman is mature but not old. Both of these perspectives lead to the prediction that hungry men will rate women with larger breasts as more attractive than satiated men, which we tested in Study 2.…”

“…On the other hand, it is possible that biomechanical constraints as a result of sexually dimorphic fat deposition placed unique demands on human female morphology, which resulted in the selection of breasts [12]. Once enlarged, sexual selection may have enhanced the expression of permanently enlarged breasts [13], with breasts variously argued to act as a sign of nulliparity, age, sexual maturity, or fertility [14]–[17].…”

Evidence to Suggest That Teeth Act as Human Ornament Displays Signalling Mate Quality

“…Age-related changes in colour mean that women’s teeth are also serving to signal residual reproductive value (e.g. [76]). Hence women smile more than men [77], [78], [79] and are the only sex to commonly enhance the prominence of their tooth displays by the wearing of lipstick [80].…”