Pornography, however, is a term that would have no meaning in Huxley’s “World State” — or, rather, its meaning would be the reverse of the one it has now. This is in keeping with the sexual topsy-turviness of Huxley’s dystopia, which turns all our taboos inside out. In “Brave New World,” the most obscene word, the one that has the power to make people blush and flee the room, is “mother.” The most antisocial sexual behavior is monogamy, and a man is a “perfect gentleman” if he refrains from paying too much attention to any particular one of the women he’s sleeping with. All this is because, in Huxley’s meticulously imagined future, the cardinal virtue is satisfying your appetites, and the worst vice is repression.

When we talk about “Brave New World,” we usually have in mind the novel’s vision of a society stratified by scientific means into predestined castes — the handsome, intelligent Alphas lording it over the moronic, undersized Epsilons. But the truth is that the novel’s understanding of embryology, and its crudely behavioristic ideas of conditioning, are both badly dated. The more we learn about human nature, the clearer it becomes that it can’t be manipulated as straightforwardly as Huxley imagined.

What has come true in “Brave New World,” to a much larger extent, is the liberation of sexuality. If you compare our generation to Huxley’s, there’s no doubt that we listen to more explicitly erotic music, wear more revealing clothing, form and break sexual attachments much more casually, and teach our children to be free from sexual shame — all things he predicted, queasily, in his novel. There may not yet be a musical instrument called a “sexophone,” but the Internet has done more to make sexual images, and sex itself, available than anything Huxley imagined.

For Huxley, who was born when Queen Victoria was on the throne, sexual freedom was inevitably going to translate into emotional shallowness. Without sublimation, there is no culture: That is the Freudian premise of “Brave New World.” If, today, Huxley’s novel often feels snobbish and reactionary, it is because we have survived the great change and found ourselves not so degraded as Huxley expected. Yes, we live in a time of commodified sexuality, of pornography on demand and of many kinds of vulgarity; Huxley, transported to the year 2013, would smile grimly.

But “Brave New World” was wrong about the essentials. People still seek intimacy and even monogamy, but on a new basis; sexual freedom has given our relationships more dignity, because they are based on choice and not frustrated need. Nor has the weakening of repression stopped us from cherishing art, science and the ideal. Human nature, in this as in other respects, is not so malleable as Huxley thought. “Brave New World” makes the illiberal assumption that giving people more freedom and less authority will degrade them. The challenge the book sets us today is to prove him wrong.