A woman’s willingness to share money or other material possessions with strangers is tied to the variation of estrogen levels produced during menstruation and ovulation. The results only apply to women that do not use synthetic contraception like birth control pills. The study conducted by Christine Anderl and colleagues at the Goethe University in Frankfurt am Main in Germany is the first to tie sharing behavior in women to estrogen levels.
The 400 women in the study were selected based on not using hormone-based contraceptives, not being pregnant, and having a natural menstrual cycle. The levels of estrogen and progesterone were estimated in each woman based on a self-report of the woman’s menstrual cycle. The women’s willingness to share resources was measured by a standard test called the Social Value Orientation that measures a person’s willingness to share fictitious money with a stranger.
All of the women were more willing to share their resources with strangers during and shortly after menstruation when estrogen levels were low. All of the women were less inclined to share resources with strangers few days after ovulation when estrogen levels were highest. This is the first study that shows a specific social behavior like sharing is tied to estrogen levels in women.
One potential explanation of the behavior is that women who are in a post ovulation phase are more likely to wish to keep resources in anticipation of possible pregnancy. The behavior may be an evolutionary response but the researchers do not rule out the possibility that the behavior cannot be controlled by thought that supersedes hormonally induced behavior. The researchers presume that women that take hormone-based contraceptives may be more willing to share their resources all of the time because estrogen levels are kept low artificially.
