GENEROSITY: An Enhancement, by Richard Powers. A Frances Coady Book/Farrar, Straus and Giroux, 296 pp., $25.

No other major American novelist places science front and center in his fiction more often than Richard Powers.

His protagonists include a self-doubting molecular biologist ("The Gold Bug Variations") and an inspired artificial intelligence researcher ("Galatea 2.2"). In his previous novel, the National Book Award-winning "The Echo Makers," a neurological condition in which victims believe their loved ones are impostors kick-starts a story about the odd permutations of identity. For this novelist, science is not only a source of wonder and an engine of progress, but a Pandora's box of ethical dilemmas.

At the heart of Powers' new novel lies another syndrome, hyperthymia, a temperament marked by extreme, chronic happiness. "Generosity: An Enhancement" opens with a writing instructor at a Chicago art college falling under the spell of one of his students. Russell Stone can't quite believe that Algerian refugee Thassadit Amzwar is as blissfully content as she seems.

After all, the 23-year-old's father was assassinated in his country's endless civil war, and her mother has succumbed to cancer. Yet there Thassa is, seemingly hard-wired to shrug it off and focus on the upbeat. She's the polar opposite of Russell's too-bored-to-care other students. They ironically dub her "Miss Generosity."

In the plot's other major thread, scientist Thomas Kurton claims to have discovered a genetic basis for happiness, while TV science journalist Tonia Schiff piggybacks on his fame to boost her own. Eventually, a media scramble to cover what is inaccurately called "the happiness gene" expands to ensnare Thassa. Her meeting with Kurton and appearance on an "Oprah"-like TV show will doom any possibility of life outside the fishbowl.

The novel tosses out lots of themes, perhaps too many. The nature of happiness, nature versus nurture, the ethical consequences of scientific advance, information overload, loss of privacy in a world of social networking - all these jostle for our attention.

Then Powers adds the question of whether fiction itself can survive in such a media free-for-all. His narrator's intrusive interruptions to lament the novelist's inability to be heard or to tell the truth seem ham-handed and unnecessary - especially since this novel demonstrates otherwise. It keeps the reader glued to the page, eager to see whether Thassa survives the spotlight, whether Russell casts aside his fears and embraces love. What's unusual for Powers is that Kurton and Tonia shade into stereotype. The other, more important, characters grip us, and won't let us go.

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In "Generosity," Powers fuses riveting narrative and spot-on dialogue with thought-provoking social analysis. Amid the hoopla over Thassa's bliss, he highlights a crucial debate about what makes us human. If genetic engineering could make us happier, should we permit it? Are we with Kurton, who asserts that "technology changes what we think is intolerable"? Or do we side with Russell, who rebuts: "Nothing as complicated as feeling can possibly reduce to genetics"?