Human Breast Morphology and Sexual Selection

This entry was written by H Roshelle Martin as part of a project done in BIAN2133 ‘Human Reproductive Strategies’ at the Australian National University in 2019 Semester 2.


Female humans are unique in the primate world because they develop larger breasts during puberty which remain for the rest of their lives. Other female primates’ breasts are temporary, only enlarging during pregnancy and nursing. Female human breasts also have a significantly different morphology than male chests (i.e. there is a high degree of sexual dimorphism) (Dixson, Duncan, & Dixson, 2015). Breasts may communicate information about reproductive quality to potential mates. Hence, the morphology of female breasts may influence the amount of attraction from potential mates. Hence, male choice may have driven the evolution of human breast form (Havlíček et al, 2016).

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Large breasted women generally have higher oestrogen levels, which contribute to higher fertility. Breasts are also primarily comprised of fat which, along with permanent fat deposits around the buttocks, hips and thighs, provides energy required to meet the high physiological demands of pregnancy and breastfeeding. These permanent fat reserves also assist in bipedal locomotion during pregnancy by contributing to a strong centre of gravity. Hence larger breasts may have evolved together with larger buttocks, hips and thighs to sustain reproduction (Havlíček et al, 2016).

In their cross-cultural study, Havlíček et al (2016) observed that men in the Czech Republic, Brazil and Namibia preferred medium sized breasts and men in Cameroon preferred large breasts. However, all cultures preferred medium or large breasts over small breasts. Dixson et al (2011) observed that men from Papua New Guinea (PNG) showed a stronger preference for big breasts than men from Samoa and New Zealand. This variation concurs with previous studies where culturally different populations showed preferences for different sizes, or no size preference at all. The variation could be the result of cultural influences or the effect of the breasts’ relationship with other aspects of female physiology.

Communities in developing nations, in environments with higher resource scarcity or unpredictability, may show preference for larger breasts than subjects from societies with higher living standards. Dixson et al’s (2011) results support this hypothesis since subsistence farmers living in a food-scarce environment (PNG), where women engaged in physically demanding work, strongly preferred large breasts. Havlíček et al’s (2016) results were less conclusive. Cameroon has a comparatively higher maternal and adult mortality and lower per capita gross national income. The preference of larger breasts in Cameroon, then, supports the theory that fatter women are preferred in scarce or unpredictable resource communities. However, of the two Cameroonian sub-samples (university students and rural community members), the less prosperous group (rural) showed a weaker preference for larger breasts, indicative of variability in individual taste.

If men are more attracted to larger-breasted women (as several studies have shown) they may increase intrasexual competition among women. Fink, Klappauf, Brewer, and Shackelford (2014) found that mated women perceived other women with moderately large breasts as more liable poach their mates. The largest breasts in the stimuli were not perceived as the greatest threat, possibly because they were associated with being overweight and therefore less attractive.

Areola pigmentation

Dixson et al (2015) found that breast size, together with areolar pigmentation, influenced male assessments of age, attractiveness, sexual maturity, reproductive health and maternal ability. Areolar pigmentation lightens over the course of adolescence, then darkens with age, pregnancy and lactation. In the study results, small and medium sized breasts with lighter areole, and large breasts with darker areole, were perceived as more sexually mature. This supports the hypothesis that lighter areole with small to medium sized breasts signal reproductive development and darker areole with larger breasts signal full reproductive maturity. In medium sized breasts, lighter areolas were deemed more attractive than darker areolas. This may be because lighter areola on signal youth and higher residual reproductive value and medium sized breasts signal sexual maturity. Conversely, on large breasts, darker areolas were rated as more attractive than lighter areolas. They were also perceived as belonging to more maternal women. This could be because darker areola signal higher fertility since pigmentation increases with pregnancies. Dixson et al’s (2011) results more definitively showed a male preference for dark areolae as a signal of sexual maturity, over light areolae signalling nubility and youth. However preference for areola size in this study was variable, suggesting cultural variability.


Breasts lose firmness as parity and age, which reduce residual fitness, increase. That is, ptosis (breasts drooping onto the chest and flattening and nipples pointing down) increases with age and pregnancies and breasts appear more pendulous. Breasts that appear firmer, therefore, may signal youth and fewer pregnancies. This hypothesis was supported by the results from the Havlíček et al (2016) study, where men across all four cultures in their study preferred breasts that showed the least ptosis.

Symmetry might indicate high genetic quality, developmental stability and pathogen resistance in various animals, including mammals. Breast symmetry could indicate the same in human females. Past studies have found a correlation between breast symmetry and fecundity, as well as a male preference for symmetrical over asymmetrical breasts (in America, Spain and the United Kingdom). Dixson et al (2011) hypothesised that subjects living in higher-pathogen environments (i.e. PNG) would value breast symmetry. Their results did not strongly support this. While the PNG participants did show a preference for symmetrical breasts, men from NZ and Samoa showed a stronger preference.


Human females may have evolved permanent breasts as a result of male choice in sexual selection. Breast morphology may also contribute to intrasexual competition between females. Studies indicate that breast size, shape, symmetry and areolae size and pigment may convey information regarding, sexual maturity, nubility, health and ability to sustain pregnancy and lactation to potential mates. However, breast morphology interacts with other aspects of female physiology to influence male preferences. Studies have also shown the high degree of cultural and individual variability in male preferences.

Literature Cited

Dixson, B. J., Duncan, M., & Dixson, A. F. (2015). The Role of Breast Size and Areolar Pigmentation in Perceptions of Women's Sexual Attractiveness, Reproductive Health, Sexual Maturity, Maternal Nurturing Abilities, and Age. Archives of sexual behavior, 44(6), 1685-1695.

Dixson, B. J., Vasey, P. L., Sagata, K., Sibanda, N., Linklater, W. L., & Dixson, A. F. (2011). Men's preferences for women's breast morphology in New Zealand, Samoa, and Papua New Guinea. Archives of sexual behavior, 40(6), 1271-1279.

Fink, B., Klappauf, D., Brewer, G., & Shackelford, T. K. (2014). Female physical characteristics and intra-sexual competition in women. Personality and Individual Differences, 58, 138-141.

Havlíček, J., Třebický, V., Valentova, J.V., Kleisner, K., Akoko, R.M., Fialová, J., Jash, R., Kočnar, T., Pereira, K.J., Štěrbová, Z., Varella, M.A.C., Vokurková, J., Vunan, E. & Roberts, S.C. (2016). Men's preferences for women's breast size and shape in four cultures. Evolution and Human Behavior, 38(2), 217-226.

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