The original "Joy of Sex" sold 8 million copies and a slightly updated 2002 edition sold nearly 100,000 more, mostly to women, according to the publishers.
The latest overhaul -- done with a team of researchers -- "updates the importance of the clitoris, hormones, pheromones and scientific development in understanding aging and sexual problems," said Quilliam. "There was no real therapy in those days."
"Attitudes have changed completely," said Quilliam. "But we are more inhibited with a new Puritanism, compared to the '70s where Alex Comfort was living the California lifestyle and was very open to sex."
But at the same time, that generation had its own inhibitions. "A lot of people had never heard of sadomasochism," she said. "Nowadays even the most vanilla magazine recommends use of a sex toy."
"The Joy of Sex" was a sensation when it was first published in 1972, according to Pepper Schwartz, professor of sociology at the University of Washington and a relationship expert for perfectmatch.com. The book spawned other racier titles and "fermented" the Sexual Revolution.
"The influence of the original was to make it beautiful enough to be acceptable to look at," Schwartz told ABCNews.com. "Up until then, there wasn't an intermediate form of explicit pictures that wasn't pornographic."
Comfort's book was noteworthy for its detailed drawings, many of which are retained in the new version.
"They looked like nice people who, with their clothes on, would be nice to have coffee with," said Schwartz. "I don't even remember any of the writing. The pictures were unusual, letting you get a good close-up look to get new ideas and permission to try something you didn't know about."
Today's sex books would have been "over the top" by 1972 standards, added Schwartz, author of "Sex Weekend: A 48-Hour Program for Bored, Busy or Bold Lovers." Her book, too, relies on the premise of Comfort's best-seller that without variation, sex is tiresome.
"If you eat steak every day, you would be bored with it," she said. "I think they took a good approach: Strawberries are no better or worse than steak. But you want variety."
And then, as well as now, the illustrations show the reader exactly how. "What would it look like if you were making love with a woman on your lap?" she said. "A picture is worth a thousand words."
But according to writer Quilliam, readers are still looking for answers, nearly three decades later. As an "agony aunt" -- the British equivalent of Dear Abby -- she fields 25,000 letters a year.
"I get a whole age range and a lot of letters from men," she said. "They are relationship questions like the loss of desire or I still want my partner, but they don't want me."
When the book launched in Britain she took two hours of calls from readers. "Some were so basic, just so basic," she said. "I've been with my girlfriend for three months and I know this thing called the clitoris, but I don't know where it is."
"The point is there is an awful lot of information in society, but the problem is a lot of it is inaccurate, useless or positively harmful," she said. "On the Internet a man can see a photo image of women, but it would not help his sex life."
In rewriting the original "Joy of Sex," Quilliam's feminine perspective reflects much of what has changed in the world of sex in 36 years.