Menstrual Cycle

Abstract

Evidence that women are less likely to be raped near ovulation than at other times in the ovarian cycle may reflect behavioral adaptations against the risk of fertile insemination by rapists. Chavanne and Gallup [Evol. Hum. Behav. 19 (1998) 27] proposed that women selectively reduce behaviors that expose them to a risk of rape during the ovulatory phase of their menstrual cycle, and reported supportive evidence. However, their study suffered from certain methodological shortcomings. In an improved test involving 51 subjects, repeated measurement, and an explicit distinction between risky and nonrisky activities, we confirmed all predictions: During the ovulatory phase, naturally cycling women reduced risky behaviors and increased nonrisky ones. Women using contraceptives causing hormonal suppression of ovulation showed neither effect.

1. Introduction

Forced copulation is taxonomically widespread, and in many cases it clearly represents an evolved reproductive tactic (Cox & Le Boeuf, 1977; Gowaty & Buschhaus, 1998; Smuts & Smuts, 1993; Thornhill, 1980; Thornhill & Thornhill, 1987).