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Spain is moving to grant basic legal rights to apes. American law schools are offering courses on animal rights. In California it will be illegal to keep a calf, pregnant hog or egg-laying hen in a pen or cage in which the animal can't stretch or turn round.

In the New York Times, Nicholas Kristof argues that these attitudinal shifts stem from the 'deep intellectual ferment' that began with one article by Peter Singer that was published in 1973 in the New York Review of Books.