While a previous study showed that men respond differently to ovulating women, a new study holds that women’s flirting behaviour differs when ovulating, especially when in high or low fertility parts of their ovulatory cycle.

In the study, 31 women  interacted with men during high and low fertility times of their cycle, and during each interaction, displayed “purported markers of genetic fitness”. These included characteristics such as charisma, confidence, and social dominance – the “sexy cad”, and a man who was more reliable and reserved: the “good dad”.

Both men in the study was played by the same actor using different transcripts. Women preferred the “sexy cads” for short-term relationships when pregnant, but not for long-term. They also flirted more when they were fertile, but only with the “sexy cads.” Fertility was found to have a clear and precise effect on women’s behavior.