Hello NL888. I think that Dawkins is evoking Paley's design argument at the start of the paragraph: the idea that someone finding a watch on a desert island would say to himself that some intelligent creature had lived on the island - this is the ID argument. The passage you are considering seems to be looking at the idea, familiar to examiners of written university theses, that if a passage in the thesis contains identical words to a passage available on the internet, say, then the passage in the thesis has probably been lifted from the passage on the internet.
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