"I wish I knew," sighs Louanne Cole-Weston, a sex therapist in the Sacramento, Calif., area, who is the "Sex Matters" columnist for OnHealth.com. "But I'll tell you one thing: There's a surprising amount of interest in pubic hair removal. The recent column I did on it got more responses than anything else I've ever written for 'Sex Matters' -- and not just from women. Many men are interested in getting rid of their pubic hair, too. I was surprised at all the interest."

It's not easy to track the history of pubic presentation. Ancient Chinese, Greek and Roman erotic art generally depict genitals -- both male and female -- without pubic hair. Did the ancients remove it? Or did the artists simply not include it? Art historians are silent on the subject.

Trackable pubic fashion dates from the mid-19th century invention of photography. Compared with today's crotch close-ups, surviving erotic photos of nude women from the Civil War era tend to be demure. They show naked breasts and buttocks, but often not the pubic area. However, in those that show frontal nudity, the amount of pubic hair varies from full to none.

Early pornography -- the "blue movies" of the 1920s and 1930s -- show a similar range of female pubic hair, from bushy to bald.

But in recent decades, there has been a clear trend in the sex media toward bush wacking. "If you track Playboy and Penthouse over the years," explains Marty Klein, a Palo Alto, Calif., sex therapist and author of several books (most recently "Let Me Count the Ways: Discovering Great Sex Without Intercourse"), "you see full bushes through the 1970s, then from around 1980 through the present day, a steady trend toward less and less hair."

"I was a Penthouse model in the early 1980s," says retired porn star Kelly Nichols, "and I posed with a full bush. No one in adult entertainment shaved back then. Now everyone does."

"For many years, I've been a lifeguard at a pool at a large university," writes one woman contributor to the Shaving Forum on Joan Elizabeth Lloyd's Secrets for Lovers Web site, one of the many Web sites devoted to the smooth look, "so I see a lot of naked college-age women in the shower and locker room. Over the years, there's been a trend toward pubic trimming and shaving. Most college women these days keep their pubic hair trimmed short. And it's not uncommon to see them completely shaved."

But the lifeguard adds that pubic trimming might be an age-specific phenomenon: "I still see full bushes, but usually on high school girls, or women out of college, in their mid-20s or older."

"The trend toward shaving might just be fashion," Cole-Weston speculates. "In another 10 years, the full look might return."

Unlikely, says Betty Dodson, a sex educator based in New York City, and producer of "Viva La Vulva," a video celebrating the beauty of women's genitals: "I think we have changing ideas about what's public and what's private. Nudity is less private than it used to be. When women's clothing began showing bare arms and legs in the 1920s, leg and underarm shaving followed soon after. Not all women shave their legs and armpits, but most do. And now that nudity is more public -- nude beaches, routine nudity in film, and the enormous amount of exhibitionism and porn on the Web -- I'm not surprised to see a trend toward pubic shaving. I think it's probably here to stay."

If anyone should know how the porn stars get so smooth, the producer of "Viva la Vulva" should. "Honey," Dodson says, "I have no idea."