Social historians of the future will stroke their chins over a phenomenon that flourished at the start of the 21st century. Scores of European and American movie, television and recording stars, all blessed with fame, money, adulation and public exposure, were seized by a sudden desire to be filmed having sex.
Not only that: in almost every case, their joy in being able to watch the deployment of their limbs and fleshy extremities in acts of penetration and emission swiftly turned to dismay as the resulting private footage was released commercially, to be gawped at by prurient members of the public.
The combination of extreme exhibitionism and mortified embarrassment was a new milestone in the evolution of the human ego. The appeal of making a sex tape may be hard to fathom, but they've been popular for a while.
The first example of in flagrante filming wasn't a tape but a Polaroid photo – that of Margaret, Duchess of Argyll, fellating an unknown man (thought to be Douglas Fairbanks Jnr) while wearing nothing but a triple string of pearls. The compromising snap did the rounds of high society and turned up as evidence in the Argylls' bitter divorce case in 1963.
A sex tape allegedly showing Marilyn Monroe pleasuring herself with a Jurassic-era vibrator has been around for years.
Another, showing Jimi Hendrix enjoying the eager attentions of two hippie girls in 1967 was locked away for 30 years before being made public.
More recently, Paris Hilton, Britney Spears, Lindsay Lohan, Colin Farrell, Nicki Minaj and Kim Kardashian have all expressed horror, in varying degrees of plausibility, at discovering the great unwashed have been able to examine and criticise not only their naked crevices but their Reverse Cowgirl/boy technique.
The responses of the participants have been many and varied. Some claimed the tapes were fake. Some, such as Tommy Lee and Pamela Anderson, shrugged off criticism of their behaviour, content in the knowledge that their bodies had been revealed as impressively awesome.
Kim Kardashian initially denied that a sex tape of her and an ex-boyfriend existed, then, when the tape became a bestseller in adult video stores, sued the distributors for violating her right to privacy and won an out-of-court settlement for $5 million.
None, until now, has tried to put a human face on what is generally held to be typically sleazy "celebehaviour".
This week Tulisa Contostavlos, of the N-Dubz rap combo and The X Factor judging panel, startled the gossip community by making a five-minute tape, not of sex, but of explanation, after mobile-phone footage of her was leaked online allegedly by an ex-boyfriend called Justin "Ultra" Edwards.
With her hair scraped back and her face lit like the girl at the end of The Blair Witch Project, she explained how "devastated" she was by the betrayal of someone once so close to her.
"I practically moved in with him," she tearfully explained. "I loved him deeply, had a lot of respect for him, we talked about kids and marriage. I got my record label to give him a singles deal."
She revealed that she'd learned, six months earlier, that Edwards was threatening to release the footage "for whatever reason – to make money, or ruin my career" and had confronted him, to be met by his denial. She asked viewers to understand that, "When you share an intimate moment with someone you love, that you care about and trust, you never imagine that at any point it will be shared with the rest of the UK or people around the world."
It looked and sounded like a genuinely heartfelt confession in a milieu where couples routinely abuse and attack each other. But it wasn't clear whether Tulisa was apologising for the existence of the tape, or asking for sympathy that it had gone public.
Her video was an indignant rejection that she should be thought a woman of loose morals just because she has joined the ranks of Kim, Pam, Britney et al. That seems to be the moral in this story: the fact that your naked body and hungry mouth are splashed all over cyberspace doesn't make you a slut. It means you've been taken advantage of by someone you trusted, even while he was filming your "intimate moment".
Also, although your PR might say the video was "100 per cent fake", you can later admit that it was 100 per cent authentic, provided you tell the world "I'm not going to sit here and be violated or taken advantage of" – as though the truth captured on videotape is contingent on another form of truth, to which only you have access.
The rules that operate in Planet Celebrity are inscrutable indeed.
There is, however, one rule which should by now be self-evident: the minute your sexual partner brings out the iPhone, the Canon or the Nikon, put your pants back on and call a taxi.