Christie's has just sold two iconic works of art by Andy Warhol for record sums. By far the more expensive was Green Car Crash, which sold for more than £36m; few of the papers reporting the story, however, bothered to reproduce the picture itself. Instead, the less pricey Lemon Marilyn, a snip at £14m, graced the front pages - because even when she costs less, Marilyn always sells more.
In 1945, when at the age of 19 she was successfully modelling as Norma Jeane Dougherty, an advertising association named her "The Most Advertised Girl in the World!". Even with a different name, she's still making everyone else rich. Warhol's coloured Marilyns are some of the most recognisable, and valuable, 20th century works of art, each now worth about the same as a Van Gogh.
When Marilyn Monroe died, she left the bulk of her estate to her mentor, Lee Strasberg, requesting that he distribute her personal effects among her friends. Legal wrangling delayed the settling of the estate for decades; the lot was inherited by Strasberg's third wife, Anna, whom Marilyn never met. In 1999 Christie's sold some of the effects, which were not given to friends, for $13.5m (£6.8m). Marilyn's driver's licence sold for $145,500; two snapshots of her poodle went for $222,500; her piano was purchased by the singer Mariah Carey for $632,500; the dress she wore to sing Happy Birthday to John F Kennedy at Madison Square Garden was bought for $1.26m.
When Marilyn became the centrefold of the first issue of Playboy magazine in 1953, she neither gave consent nor received payment. For $500 Hugh Hefner had bought the negatives of a nude 1949 photoshoot, for which the then struggling starlet had been paid $50. He became a millionaire over Marilyn's nude pictures; she never made another dime from them.
No one outside the art world had heard of Warhol until Marilyn died in August 1962. Using a publicity photo advertising Niagara, a 1953 film, Warhol launched his career over Marilyn's dead body. Lemon Marilyn was bought in late 1962, after Warhol's first one-man show, for $250. It is now approximately 112,000 times more valuable. And Marilyn? She has become a cartoon with a purple face. Clearly Warhol stumbled on to something in the cultural psyche with those garish, stylised silkscreens - call it an inclination for travesty.
Our fondness for these cartoons hardly suggests a shared aesthetic of subtlety or discrimination - now only a bad word. Critics maunder tirelessly about the oracular meaning of these prints: apparently, they reveal astonishing insight into the processes of commodification, into the manufacturing of celebrity, or - they say - into the nature of Marilyn. Some even say the prints acknowledge Marilyn's talent for self-fashioning, which at least is generous, if wishful, thinking. Clearly, Warhol is taking all the credit, and these supposed revelations are mostly cultural cliches.
In addition to his famous quip guaranteeing us all the right to 15 minutes of fame, Warhol opined that "repetition adds up to reputation". These observations have become edicts: everyone feels entitled to 15 minutes; reputation now comes only from repetition. It is not pious nostalgia to point out that we are evacuating our values of meaning: reputation once meant character; fame once meant honour. The old studio system was no slouch at exploitation, but Hollywood once made movie stars by creating franchises out of personality; now it creates franchises out of spin-offs. We live in a world of derivatives, and Warhol's many Marilyns helped get us there. The price we continue to pay for them is not really £14m. It's that we can no longer tell the difference.
· Sarah Churchwell is the author of The Many Lives of Marilyn Monroe