A woman's voice becomes more attractive when she is most fertile. That's according to Nathan Pipitone and Gordon Gallup of the State University of New York at Albany.

The pair recorded women counting from 1 to 10 at four occasions during their menstrual cycle. They then replayed the recordings at random to male and female students and asked them to rate the attractiveness of the voices. Both males and females judged the women's voices to be most attractive if they were recorded during the peak fertility period of the menstrual cycle, and less attractive if they were recorded during non-fertile periods (Evolution and Human Behavior, DOI: 10.1016/j.evolhumbehav.2008.02.001).