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Before the 1858 publication of On the Origin of Species, Charles Darwin developed his theory of natural selection in five notebooks. In them he first expressed one of natural selection's principles: that species produce more offspring than available resources can sustain. He also listed books he read, such as Charles Lyell's Elements of Geology. A fall 1838 entry in one of Darwin's notebooks mentions species struggle for survival in a world of insufficient resources "as inference from Malthus," referring to a 1798 essay by economist Thomas Malthus asserting that population growth will outpace agricultural production. A later notebook, begun in October 1838, mentions "the grand crush of population." This suggests that ____