Breast Symmetry and the Menstrual Cycle.

Psychology Today

Homo Consumericus

The Nature and Nurture of Consumption
Is she ovulating? Watch her breasts.
Published on August 2, 2010
An ongoing debate amongst evolutionists is the extent to which human females experience cryptic ovulation. Of course, if compared to some of our animal cousins, women experience less conspicuous advertisements of estrus. However, there are certain subtle morphological features that change as a function of where a woman is in her menstrual cycle. One such trait is the extent to which a woman’s breasts are symmetric. Whereas there are clear inter-individual differences in breast asymmetry, this metric also varies within women as a function of their ovulatory cycle. On a more somber note, several studies have revealed a link between breast asymmetry and breast cancer (see here and here).

John Manning and his colleagues set out to test the cyclic asymmetry of several traits including women’s ears, digit ratios, and breasts (this last one being a sexually selected trait). Of relevance to today’s post, the researchers used cranio-caudal mammograms of 280 premenopausal women to calculate their breast asymmetry, with thirty-four of the women having used oral contraceptives within the two months prior the mammography. The data contained the necessary information to establish on which day of a woman’s menstrual cycle the mammogram was taken. Accordingly, Manning et al. could test whether scores of breast asymmetry varied across the cycle.


Author: Leslie Carol Botha

Author, publisher, radio talk show host and internationally recognized expert on women's hormone cycles. Social/political activist on Gardasil the HPV vaccine for adolescent girls. Co-author of "Understanding Your Mood, Mind and Hormone Cycle." Honorary advisory board member for the Foundation for the Study of Cycles and member of the Society for Menstrual Cycle Research.