At least for humans, this most basic of acts is anything but basic. As the pioneering sex researcher Alfred Kinsey put it, the only universal in human sexuality is variability itself. From attraction to action, sexual behavior takes many forms. Human interest in sex is not a matter left to chance but more a built-in imperative; survival of the species depends on it. The decks are stacked in sex's favor, as a passport to bonding, to intimacy, to pleasure, and even to human growth and healing. Bodies and interests change over the course of time, and the complexities of physiology and psychology mean that most people experience a sexual problem at some point in their lives. Although sex can be one of the most difficult topics for partners to discuss, it's one that also stands to draw couples closer together. The moral and political implications of sex vary greatly from culture to culture, and even within cultures and over time; still, there is agreement on one certainty: It's why we're alive today and what future generations depend on.
The Fundamentals of Sex
The Science of Desire
Desire is part biology, part psychology, often as subtle as it is predictable, and takes shape differently in men and women. For men, arousal typically precedes desire. But for women, desire precedes arousal, in response to physical intimacy, emotional connection, and an atmosphere free of distractions and everyday concerns. Scientists are continuously exploring the interplay of biological influences, such as neurohormones that suppress or enhance desire, and psychological influences, such as emotions and relationships. Smell plays an often subtle role in attraction; research shows that women are attracted to mates whose natural body odor (sometimes referred to as pheromones) signals a genetic profile distinct from their own. Low sexual desire is a common occurrence, among both sexes, and often it can be resolved by regularly exchanging affection and conversation outside the bedroom as well as in it, making sufficient time for each other and for sex, and addressing conflicts within a relationship.
The pleasure of sex arises from many factors including the release of neurochemicals such as oxytocin and dopamine, which flood the system during orgasm, as well as the sense of connection communicated by touching, massaging, and cuddling. Given the enormous variability in activities that people find arousing, there is no one way to be sexual. Men are especially stimulated by visual imagery, and about 90 percent of young men report using pornography with some regularity, often because they lack a partner or don't know how to bridge the differences in sexual appetite and interest that can occur between partners in the absence of discussion of their sexual pleasures. Many people engage in behaviors that were once perceived as atypical, such as dominance play and anal intercourse. Researchers know that flexibility in sexual repertoires is healthy and generally enhances relationships; they regard a specific behavior as problematic only when it creates harm or distress for one or both partners or when the behavior is compulsive—that is, it becomes the only means of arousal. "Sex addiction" is a label often used to suggest excessive interest in sex, but studies show it may be more related to the moral/religious environment in which a person lives.
Sex and Age
Sexual behavior changes over time as a reflection of age, experience, and one's relationship. And the trajectory of change may vary between men and women. Women may encounter difficulties in navigating cultural attitudes about sexual behavior and promiscuity as they first explore their sexuality; age brings confidence and skill at communication that can enhance sex life. Young men often have concerns about performance, penis size, or premature ejaculation—and anxiety is no friend to performance for either men or women. Men often experience challenges with arousal and erectile dysfunction as they age. Couples tend to report that their sex life is most robust when they are in their 30s and 40s, but sex life is often most deeply rewarding for older partners. People can enjoy satisfying sex throughout the lifespan if they make adjustments for the many changes that time brings; that can mean relying less on penile penetration and more on massage, whole-body touching, and oral sex.