Many of the fans milling into this year’s postseason baseball games have been wearing authentic major league uniforms, with GUERRERO, say, or OSWALT, stitched on the back. True, society has traditionally encouraged kids to fantasize about what they’ll be as adults. But most of the people I’ve seen in $200 regulation shirts are adults. What they’re fantasizing about is an alternative adult identity for themselves.

Why do they do this? The literary critic Paul Fussell once speculated that wearers of “legible clothing” like T-shirts were merely losers trying to associate themselves with a success, whether it be a product (Valvoline) or an institution (The New York Review of Books). A conservative view held that dressing like a child meant shirking the responsibilities of adulthood. It was a subset of dressing like a slob. But these explanations do not cover the ballpark people or (to take a similar phenomenon) those weekend bicyclists in their expensive pretend-racer costumes, with European team logos and company trademarks. The message in their clothing is aimed not at others but at themselves. It is a do-it-yourself virtual reality.

Abandoning your own world for a made-up one is an ever larger part of adult life. For the futurist Ray Kurzweil, this is only the beginning. According to his new book The Singularity Is Near, we are approaching the age of “full-immersion virtual-reality.” Thanks to innovations in genetics, nanotechnology and robotics, you’ll be able to design your own mental habitat. You’ll be able to sleep with your favorite movie star – in your head. (It is not lost on Kurzweil that you can already do that, but he insists it will be really, really realistic.) Those same technologies will help us “overcome our genetic heritage,” live longer and become smarter. We’ll learn how brains operate and devise computers that function like them. Then the barrier between our minds and our computers will disappear. The part of our memory that is literally downloaded will grow until “the nonbiological portion of our intelligence will predominate.”

But this raises questions: What will then be the point of unenhanced human beings? And what will become of our relations to one another? A willingness to run head-on at these moral-technological issues has made the French novelist Michel Houellebecq one of Europe’s best-selling writers and arguably its most important. His Elementary Particles (2000), set in the year 2079, recounts the near-total extinction of ordinary human beings. His new novel, “The Possibility of an Island,” due out in the United States next spring, describes the triumph of a cult that believes man was created by nondivine extraterrestrials and sees genetic engineering as a path to “immortality.”

The novel cuts between a sex-obsessed comedian, Daniel1, and two of his enhanced clones, Daniel24 and Daniel25. It would not surprise Houellebecq that Kurzweil, like other technological optimists, should use sex to sell his utopia. For Houellebecq, the important line the cult crosses is not a scientific but an anthropological one. By making credible promises of longevity and sex, it manages to elevate materialism (more specifically, consumerism) into a religion. Daniel1’s girlfriend, the editor of a magazine called Lolita, explains, “What we’re trying to create is an artificial humanity, a frivolous one, that will never again be capable of seriousness or humor, that will spend its life in an ever more desperate quest for fun and sex – a generation of absolute kids.”

But something gets left out of sex when it is idealized, marketed, venerated or souped up: other people. Regardless of whether your girlfriend can handle your sleeping (virtually) with Angelina Jolie, it is very likely you’ll find the hard work of maintaining a relationship less rewarding when so many starlets beckon. Americans may be surprised that Houellebecq attributes the bon mot about masturbation being sex with someone you love not to Woody Allen but to either Keith Richards or Jacques Lacan. But whatever its source, the narrator Daniel25 views it as one of the more profound insights of our time.

Human interactions of all kinds, especially those that involve caring for others, appear less and less worth the trouble. Houellebecq is fascinated by young couples who have pets instead of children, and by the French heat wave of 2003, which killed thousands of senior citizens who were forgotten by their vacationing children and abandoned by their vacationing doctors. Daniel1 mocks the newspaper headline “Scenes Unworthy of a Modern Country.” In his view, those scenes were proof that France was a modern country. “Only an authentically modern country,” he insists, “was capable of treating old people like outright garbage.”

If we treat our fellow humans this way, why should we expect posthumans to care for us any better? We shouldn’t. In the novel, when an acolyte witnesses a murder that, if revealed, could derail the cult’s DNA experiments, the chief geneticist orders her thrown from a cliff. He feels no shame, nor does the narrator see any reason why he should. “What he was trying to do,” Daniel1 writes, “was to create a new species, and this species wouldn’t have any more moral obligation toward humans than humans have toward lizards.”

In his recent book, Radical Evolution, Joel Garreau suggests a “Shakespeare test” to determine whether Prozac or cloning or full-immersion virtual reality robs us of our humanity: would the user of these innovations be recognizable to Shakespeare? Houellebecq suggests that the answer is tipping toward No. “Nothing was left now,” Daniel25 notes, “of those literary and artistic works that humanity had been so proud of; the themes that gave rise to them had lost all relevance, their emotional power had evaporated.”

Many Westerners looking to the future think they’re about to attain the prize of a fantasy-filled high-tech life that lasts until a ripe old age. Houellebecq warns that second prize may be a fantasy-filled high-tech life that lasts forever.