Natural Selection

Barthelme's bracingly cynical novel of marital discord and midlife crisis in a Houston suburb aches with tenderness and hurt. At 40 Peter Wexler feels ``stuck in the job, in the life, marking time.'' He tells his nine-year-old son things like ``You're small and sort of dumb.'' Coming unhinged, Peter separates from his second wife, Lily, an arts administrator who is adept at baby-sitting his depressions. Before Peter reunites with Lily on their kitchen floor, he will do much soul-searching and make love to her strung-out ex-sister-in-law on the front fender of a Chevy. Not bad for a guy who agonizes over whether his marriage was based on ``frightened-of-loss longing,'' a PR hack who concocts tiny wind-up ape toys for ``ape concept promotions.'' The Darwinian overtones of the novel's title take on a dark irony in the shattering, unforeseen finale, whose senseless violence echoes the angst of all the characters. (Aug.)