Darn, I keep saying that we Boomers invented sex, but I'm wrong.
According to an article by Roger Dobson in the Sunday Times Online (UK), prehistoric men and women left evidence of a swinging lifestyle: bondage, group sex, sex toys, and other evidence that even then, people recognized that sex was for fun, not just for procreation.
Dobson interviewed Timothy Taylor, reader in archeology at Bradford University, who reviewed evidence from dozens of archeological finds and scientific studies. “The widespread lay belief that sex in the past was predominantly heterosexual and reproductive can be challenged,” said Taylor. Intercourse, Taylor says, was "a vital part of social interaction, communication and inventiveness." His research has been published by Haworth Press in the Handbook of the Evolution of Human Sexuality.