“Evolution must have involved the simultaneous change in many genes, which doubtless accounts for its slowness. Here matters would have been easier if heritable variations really formed a continuum, as Darwin apparently thought, i. e. if there were no limit to the possible smallness of a variation. But this is clearly not the case when we are considering meristic characters. …the atomic nature of Mendelian inheritance suggests very strongly that even where variation is apparently continuous this appearance is deceptive.”

Source: The Causes of Evolution (1932), Ch. IV Natural Selection, pp. 103-104.

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J. B. S. Haldane 32
Geneticist and evolutionary biologist 1892–1964

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