"Credit, or blame, the Internet, making information available in such a level playing field that outrageous acts have become so accessible they seem mainstream," she told ABCNews.com.
Throughout history kinky sex has emerged in myth, literature and in anthropology. Urban legends still persist that Catherine the Great had a special relationship with her horse.
Dunlap cites studies that in some African cultures, older women guide younger boys into their manhood and are "revered."
But today, according to sex-perts, couples are looking for more intensity in sex lives, and interest in sado-masochism appears to be rising.
"After the pain threshold is crossed, they describe a type of ecstasy called 'flying," Dunlap found in his research. "It is no longer painful and gives an entirely sexual as well as psychological, transcendent place. Flying is bigger than any drug."
British relational therapist Susan Quilliam, whose revision of the 1972 classic, "Joy of Sex" sold 30,000 copies in three weeks when it was released this year in the U.S., confirms, "A lot is changing culturally."
"First of all, we live in a more sexualized society and there's the Internet," she told ABCNews.com. "Interest groups communicate with each other and reinforce their identity."
"It gives people permission and normalizes it and encourages them to explore the outer boundaries of their preferences," she said.
And now, her spin-off book, "The Adventurous Lover," is being billed as "perfect for the couple who want to push the boundaries: sections include fantasy, fetish, sex-clubs, foursomes and bondage."
Quilliam, who doles out advice on her "Sex in the City" radio show, has seen an increased interest in BDSM – or bondage, dominations, sado-masochism, as well as "swinging."
Creating a "safe" arena for experimentation is critical, she said, and couples should have special words, should they be uncomfortable, to call for "an immediate halt to the activity."
She also warns, "Be careful, very careful if have a fantasy and you're putting it in to reality. It often disappoints."
"It has to be safe, sane and consensual," she said.
According to Hani Miletski, a Maryland sex therapist and author of the 2007 book, "Mother-Son Incest: The Unthinkable Broken Taboo Persists," a search for the words "mother son incest" yields nearly two million links on the Internet. Clearly an abusive behavior, she said it "breaks down the natural development of boys' sexuality."
Miletsky wrote another book -- "Understanding Bestiality and Zoophilia" -- after one of her patients admitted a "love affair" with his dog. She interviewed nearly 100 men who had indulged.
"People do it with all kinds of animals," she told ABCNews.com. "A lot of people are into dolphins and other sea animals."
"We also found a minority who prefer animals to humans," she said. "It's like a sexual orientation and they marry animals and treat like spouse whole love affair."