Sex is a necessity and a pleasure; it's also a problem. It exalts some, degrades others. It generates offspring. It's dynamite. Taboos concerning it are as old as humanity. Laws regulating it predate civilization. Nowhere is the human libido absolutely unfettered. Incest is nowhere tolerated, marriage in some form, until very recently, everywhere requisite to socially sanctioned coupling.

Prostitution is called the world's oldest profession. That it is so testifies to something lacking in marriage. Even in early Japan, where a nobleman could take as many wives as he pleased, the trade flourished. Prostitutes were known as asobi-onna (women of pleasure; asobi for short). A courtier named Oe Yukitoki (955-1010) writes, "The younger women melt men's hearts with rouge and powder and songs and smiles, while the older women give themselves the jobs of carrying the parasols and poling the boats."

Boats. It was, in part, a riparian trade. "By the end of the 10th century," explains historian Janet Goodwin in "Selling Songs and Smiles," "asobi had developed their distinctive practice of using small boats to stage entertainments for men at ports" on rivers near Kyoto, the capital. She quotes a courtier writing a friend to propose a visit to a boat: "In one evening of delight, we'll forget that we must grow old."