I would like to defend the untutored reaction of incredulity to the reductionist neo-Darwinian account of the origin and evolution of life.3 It is prima facie highly implausible that life as we know it is the result of a sequence of physical accidents together with the mechanism of natural selection. We are expected to abandon this naïve response, not in favor of a fully worked out physical/chemical explanation but in favor of an alternative that is really a schema for an explanation, supported by some examples. What is lacking, to my knowledge, is a credible argument that the story has a nonnegligible probability of being true. There are two questions. First, given what is known about the chemical basis of biology and genetics, what is the likelihood that self-reproducing life forms should have come into existence spontaneously on the early earth, solely through the operation of the laws of physics and chemistry? The second question is about the sources of variation in the evolutionary process that was set in motion once life began: In the available geological time since the first life forms appeared on earth, what is the likelihood that, as a result of a physical accident, a sequence of viable genetic mutations should have occurred that was sufficient to permit natural selection to produce the organisms that actually exist?There is much more uncertainty in the scientific community about the first question than about the second. Many people think it will be very difficult to come up with a reductionist explanation of the origin of life, but most people have no doubt that accidental genetic variation is enough to support the actual history of evolution by natural selection, once reproducing organisms have come into existence. However, since the questions concern highly specific events over a