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The full range of thoughts and actions that describe sexual motivation and behavior.

While sex is not necessary for an individual's survival, without it a species would cease to exist. The determinants of sexual motivation and behavior include an individual's physiology, learned behavior, the physical environment, and the social environment.

A person's sex is determined at conception by whether one out of the 23 chromosomes in the father's sperm is either X (female) or Y (male). All female eggs contain an X chromosome, so each fertilized egg, or embryo, has a genotype of either XX (female) or XY (male). Reproductive hormones produced by the gonads (male testes and female...