MATING

The union of male and female, necessary for internal fertilization, is encouraged in nature. Most lower animals have definite seasons, governed by endocrine secretions. In most female mammals, estrus, or receptivity to mating, is operative only for short periods during the year. Animals such as the cow have several such periods of estrus during the year, the dog one or two. The human female normally has a 28-day reproductive, or menstrual, cycle, with ovulation usually occurring about 14 days before the onset of the menstruation, but sexual interest in humans is more culturally determined than tied to the reproductive cycle. In most animals, copulation is preceded by a period of courtship; the courtship ritual is stereotyped to a large extent. In humans, courtship and mating practices have been strongly modified by social and religious codes of behavior set by society.