NEW YORK (AP) -- Writer Shulamith Firestone, who published her influential "The Dialectic of Sex" at age 25 and then retreated into isolation and mental illness, has died at age 67.
Firestone was found dead Tuesday in her Manhattan apartment, said her sister Laya Firestone Seghi. The death was from natural causes.
"The Dialectic of Sex: The Case for Feminist Revolution" was published in 1970 during the height of the women's liberation movement.
Firestone applied Marxist analysis to the status of women and argued that true liberation would come only when women were freed from childbearing. In Firestone's utopian future, babies would be gestated outside the womb and raised by both sexes.
"The tyranny of the biological family would be broken," she wrote.
The book joined works like Kate Millett's "Sexual Politics" and Germaine Greer's "The Female Eunuch" as a 1970s feminist standard and is still assigned in college courses.
But Firestone retreated from public life after the book was published and was hospitalized with schizophrenia in the 1980s.
More recently she became so reclusive that according to her landlord, Bob Perl, she had been dead for about a week when her body was discovered.
Firestone was beloved despite her struggles, Perl said. People often called his office to volunteer to pay the rent on her East Village apartment.
"Family, friends and strangers supported her because she so moved them with her work," Perl said.
Firestone was born to an Orthodox Jewish family in Ottawa, Ontario, and raised in St. Louis. She earned a degree in painting at the School of the Art Institute of Chicago.
She moved to New York in the 1960s and co-founded three feminist groups intended as radical alternatives to mainstream groups like the National Organization for Women.
Firestone's only book other than "The Dialectic of Sex" was "Airless Spaces," a fictionalized account of life in and out of psychiatric hospitals, published in 1998.
In addition to Seghi, survivors include her mother, two brothers and another sister.
Seghi called Firestone "a brilliant mind and a totally creative person."
"It's a great loss," she said.