Mr Robertson, who wrote a book, The Dawkins Letter, in response to the scientist's The God Delusion, claimed Prof Dawkins' visit was not to promote science but to "advance a polemic", or controversial argument.

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Now this is probably the most difficult and controversial question to answer, but it is a valuable argument worth thinking about.

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In what will no doubt be the most controversial argument in this first volume, Mr Strachan makes a convincing case for the outbreak of war in 1914 as a product of blunder and delusion, not of deliberate German aggression.

ECONOMIST: 20th-century history

Moreover, the argument that the two species were interbreeding over such a long time is, to say the least, controversial.

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