In formulating his approach to natural history in 1837–8, Darwin combined ideas and techniques from several areas, of which five are identified. But these do not show why he formulated such an all-embracing approach, going from geology to human instincts, morality, and aesthetic responses. The hypothesis presented here is that Darwin was responding to a Romantic view of natural history such as the one held by Willian Whewell. The Romantics challenged the adequacy of reductionist systems which, they said, could not explain the ‘higher’ faculties. Darwin sought a reductionist (‘materialist’) system which would meet the Romantic objections.