Faith is powerful enough to immunize people against all appeals to pity, to forgiveness, to decent human feelings. It even immunizes them against fear, if they honestly believe that a martyr's death will send them straight to heaven.

Science has taught us, against all intuition, that apparently solid things like crystals and rocks are really almost entirely composed of empty space. And the familiar illustration is the nucleus of an atom is a fly in the middle of a sports stadium, and the next atom is in the next sports stadium.

Cloning may be good and it may be bad. Probably it's a bit of both. The question must not be greeted with reflex hysteria but decided quietly, soberly and on its own merits. We need less emotion and more thought.

Nowadays theologians aren't quite so straightforward as Paley. They don't point to complex living mechanisms and say that they are self-evidently designed by a creator, just like a watch. But there is a tendency to point to them and say 'It is impossible to believe' that such complexity, or such perfection, could have evolved by natural selection. Whenever I read such a remark, I always feel like writing 'Speak for yourself' in the margin.

Never say, and never take seriously anyone who says, 'I cannot believe that so-and-so could have evolved by gradual selection.' I have dubbed this kind of fallacy 'the Argument from Personal Incredulity.' Time and again, it has proven the prelude to an intellectual banana-skin experience.

Yesterday's dangerous idea is today's orthodoxy and tomorrow's cliché.

It is possible in medicine, even when you intend to do good, to do harm instead. That is why science thrives on actively encouraging criticism rather than stifling it.