Percy Bysse Shelley was at the heart of a family whose writings contributed mightily to the development of anarchism, animal liberation, and women's liberation.
Shelley father-in-law and ideological inspiration was William Godwin, founder of philosophical anarchism and an early utilitarian. His mother in law was Mary Wollstonecraft, author of "A Vindication on the Rights of Women", viciously parodied by Thomas Taylor in his "A Vindication on the Rights of Brutes" which satirically demonstrated that Wollstonecraft's logic could also make the case for rights for animals, a position Taylor considered absurd. Yet irononically, as a neoplatonist who sought to translate the works of his intellectual forbears, Taylor would go on to translate third century philosopher Porphyry's" "On Abstinence from Animal Food", which advanced arguments remarkably similar to modern animal liberation concepts, despite having directly referenced and mocked Porphyry's work in Vindication. This is of course well known to anyone who has read Peter Singer's Animal Liberation -- he references Shelley's book and Taylor's parody as he builds his case for why supporters of women's liberation should support animal liberation in the book's first chapter. Singer, of course, is a utilitarian like Godwin. Singer learned of Taylor's parody of Wollstonecraft's book from the appendix of Henry Stephens Salt's 1892 classic Animals' Rights Considered in Relation to Social Progress.
Shelly's wife was Mary Wollstonecraft Shelly, author of Frankenstein; or, The Modern Prometheus. An analysis of the vegetarian subtext of Frankenstein constitutes a major portion of Carol Adams' The Sexual Politics of Meat: A Feminist Vegetarian Critical Theory and is also the subject of Adam's 2007 Bedside Bathtub and Armchair Companion to Frankenstein.
"Best known as a poet and leading voice of the Romantic movement in English literature, Percy Shelley was also a social reformer who campaigned for the rights of the poor and working people not as a matter of charity, but as a question of social justice.
An advocate for unions, socialism, and animals’ right not to be exploited and slaughtered for our benefit, Shelley was among the first important spokespersons in the modern era to regard our treatment of animals as a progressive political issue on a par with our treatment of other human beings.
A Vindication of Natural Diet is an extended version of a long footnote that Shelley appended to the narrative poem Queen Mab, published in 1813, which recounts his vision of a future Utopia. Shelley regarded the slaughter of animals for food as the root crime of the human race and the ultimate cause of all of our other crimes and sorrows. In Vindication, he speaks of Prometheus as a criminal who brought evil into the world by giving humans fire with which they could make animal flesh edible by cooking it, thus bringing about the slaughter of animals for food. A vegetarian diet, with the attendant end to the slaughter of animals, would, Shelley believed, inevitably lead to the end of crime, poverty, war, capitalism, and all forms of social injustice."
-- The Animals’ Top Forty: the forty most important books (including several shorter works) in the history of animal advocacy by Norm Phelps
Here's the complete text of A Vindication of Natural Diet: