THE march of sex-selective abortion in Asia seems relentless. Not every society adopts the practice, but those that do—and they include the two largest countries on earth—have seen it spread through every social group, unhampered by growing wealth. Indeed, middle-income couples seem more willing and better able to manipulate the sex of their children than are the poor. And they are more likely to want smaller families, increasing the premium on sons in countries where males are seen as more valuable.