All domestic animals have been improved enormously by scientific breeding, and it is not open to question that human beings could, by similar methods, be changed in any desired direction. It is, of course, much more difficult to determine what we desire in human beings. It may be that if we bred people for physical strength we should diminish their brains. It may be that if we bred them for mental capacity we should render them more liable to various diseases. It may be that if we sought to produce emotional balance we should destroy art.
Source: Bertrand Russell :Marriage and Morals, 1929
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