Hollywood movies would have you believe that you can have sex without taking the time to remove your underwear (or wetsuit). You can also make love effortlessly in a standing position, with both of you climaxing quickly—simultaneously, of course, and while making attractive sounds and facial expressions. At the other extreme is modern pornography, in which coupling (if I may use that word to refer to activities that often involve a roomful of people) is fantastically prolonged and explicit.

What really goes on in the bedroom? Perhaps the cameras should be trained on the largest and most important sex organ, the brain. That's where physical and psychological stimuli get translated into signals important to arousal and orgasm, a process that brain imaging is beginning to reveal, as described in “The Orgasmic Mind” and “Lust's Reward.” Humans might even have a nerve in the head that detects erotic chemical messages (“Sex and the Secret Nerve”).

The brain plays a critical role in our response to locking lips and in sexual dysfunction, explored in articles about the act of kissing (“Affairs of the Lips”), and a surprisingly miserable affliction (“When Arousal Is Agony”). This special edition also reveals what neuroscientists and psychologists have to say about bisexuality, sexual preferences and gender identity in articles such as “Bisexual Species,” “Do Gays Have a Choice?”, “The Truth about Boys and Girls” and “Transgender Kids.”

Science is struggling to catch up with radical transformations in attitudes toward love and sex: In the U.S., the majority of adults now see nothing wrong with premarital intercourse. Sex between people of the same gender has become widely accepted, and gay marriage is legal. Consideration for the rights of transgender people is growing. Pornography is readily available online and heavily consumed, though rarely discussed. (The good news is that it's harmless to most people, as “The Sunny Side of Smut” explains.) The Internet has also become a popular hangout for people seeking partners, and the rise of mobile dating has made hookups easier than ever, as the authors of “Dating in a Digital World” lay out in their guide to online dating.

Some things haven't changed, though, as “Lust for Life” and “The Happy Couple,” respectively, suggest: pure sexual desire and a focus on positive emotions make for happily-ever-after relationships. If not good movies.