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THE birth of Louise Brown, the first child to spring from an egg fertilised outside the body, caused a sensation in 1978. Fertility experts hailed it as a breakthrough while critics attacked IVF as immoral and dangerous. Now, a quarter of a century later, we may be witnessing the start of another revolution in assisted reproduction that will be no less controversial. Last week, researchers in the US reported that they had transformed mouse embryonic stem cells into mature eggs in the lab, and a Japanese team has produced sperm in a similar way (see “The next IVF revolution?”).…