Anthropologists have been interested in menstruation from numerous perspectives, which include the cross-cultural attitudes toward it, its evolutionary significance, variations in ovarian function across populations, and the health implications of the menstrual cycle. Some cultures celebrate this visible sign of women's reproductive powers while others regard it as a pollutant. Several theories have been proposed to understand the evolutionary and adaptive significance of menstruation, which include ridding the body of pathogens, the metabolic costliness of maintaining the endometrium, and maternal self-protection. A much greater understanding of ovarian function and its relationship to many factors such as living conditions, energetics, and nutritional status, has been attained. Cross-cultural attitudes toward menstruation continue to vary and are a significant area of interest in light of the introduction of cycle-suppressing contraception. The suggestion that hormonally-induced amenorrhea is healthy because it represents an ancestral condition of few lifetime menstrual cycles is challenged.