There are three separate forces that drive all human behavior: biology, psychology and society. These forces work together in a complementary and integral fashion, and all must be considered in any attempt to understand human sexuality. Psychologists originally explained human sexuality as a biological need to reproduce, a built-in instinct. But when scientists observed homosexual behavior in the lower primates, who have no higher thoughts for reproduction, they concluded that such animals were engaging in sexual acts merely for pleasure, and revised their theories. Currently, the leading explanation is that sex is a psychological desire for sensory pleasure.
Scientists have two leading psychological explanations for the human sex drive. The first is that psychological factors are representative of biological factors, that our thoughts about sex are expressions of our needs. The second is that our patterns of human sexual behavior are acquired through psychological and social mechanisms: we use sex as a vehicle for obtaining and sustaining love, it is an important part of our self-esteem, it develops our sexual identity, and is part of one’s moral and spiritual identity. Socially, sex functions as a form of communication in a relationship, and often symbolizes a person’s status.
With human beings, similar circumstances for learning sexual behavior can be observed. Often, the first sexual experiences, the most intense experiences and the latest experiences have the maximum effect on subsequent behavior. Surveys of sexually active men show that individuals may be involved in relationships that fluctuate between homosexual and heterosexual within the same year, month, week, or even day. “No matter how strongly conditioned an older person may have become to a given class of sexual stimuli…the acquisition of new tastes remains a possibility”.