The Na of China, farmers in the Himalayan region, live without the institution of marriage. Na brothers and sisters live together their entire lives, sharing household responsibilities and raising the women's children. Because the Na, like all cultures, prohibit incest, they practice a system of sometimes furtive, sometimes conspicuous nighttime encounters at the woman's home. The woman's partners -- she frequently has more than one -- bear no economic responsibility for her or her children, and "fathers," unless they resemble their children, remain unidentifiable. This lucid ethnographic...