but it is referred to in the book as AF 632. From birth, members of every class are indoctrinated by recorded voices repeating slogans while they sleep (called "hypnopædia" in the book) to believe their own class is superior, but that the other classes perform needed functions. Any residual unhappiness is resolved by an antidepressant and hallucinogenic drug called soma. The biological techniques used to control the populace in Brave New World do not include genetic engineering; Huxley wrote the book before the structure of DNA was known. However, Gregor Mendel's work with inheritance patterns in peas had been rediscovered in 1900 and the eugenics movement, based on artificial selection, was well established. Huxley's family included a number of prominent biologists including Thomas Huxley, half-brother and Nobel Laureate Andrew Huxley, and his brother Julian Huxley who was a biologist and involved in the eugenics movement. Nonetheless, Huxley emphasises conditioning over breeding (nurture versus nature); human embryos and fetuses are conditioned through a carefully designed regimen of chemical (such as exposure to hormones and toxins), thermal (exposure to intense heat or cold, as one's future career would dictate), and other environmental stimuli, although there is an element of selective breeding as well. Comparisons with George Orwell's Nineteen Eighty-Four In a letter to George Orwell about Nineteen Eighty-Four, Huxley wrote "Whether in actual fact the policy of the boot-on-the-face can go on indefinitely seems doubtful. My own belief is that the ruling oligarchy will find less arduous and wasteful ways of governing and of satisfying its lust for power, and these ways will resemble those which I described in Brave New World." He went on to write "Within the next generation I believe that the world's rulers will discover that infant conditioning and narco-hypnosis are more efficient, as instruments of government, than clubs and prisons, and that the lust for power can be just as completely satisfied by suggesting people into loving their servitude as by flogging and kicking them into obedience." Social critic Neil Postman contrasted the worlds of Nineteen Eighty-Four and Brave New World in the foreword of his 1985 book Amusing Ourselves to Death. He writes: Journalist Christopher Hitchens, who himself published several articles on Huxley and a book on Orwell, noted the difference between the two texts in the introduction to his 1999 article "Why Americans Are Not Taught History": Brave New World Revisited In 1946, Huxley wrote