Response rates were low, which increased random variation from one period to the next.

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The small effect was just a random variation, not due to the treatment.

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But are accident black spots simply the result of random variation or are there some areas where speeding is a particular danger?

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But natural selection requires random variation to generate the various properties.

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The short answer is: calling into question whether the processes of random variation and natural selection are all we really need in order to understand the origin of species.

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In other words that if the occurrence of something is abnormally high or abnormally low simply because of random variation, the statistical chances are that it will be much closer to the average the next time you measure it.

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Retrotransposons could provide that variation, by affecting gene expression at random, depending on where they pitch up.

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