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In The Descent of Man (1871) I applied evolution to human origins, society and mental abilities and developed sexual selection; in The Expression of the Emotions (1872) I traced human psychology back to animal behaviour.

In November 1854 I realised why descendants of one species differ more and more: each becomes adapted to "diversified places in the economy of nature". This principle of divergence completed my theory.

Critics said my theory failed because it did not explain the origin of life. I answered that science accepted Newton's law of gravity though the cause of gravity was unknown.

In my 1837 B notebook I sketched descent as a single branching tree and wrote that "It is absurd to talk of one animal being higher than another", discarding Lamarck's ladder of progress.

I built my research data by questioning expert naturalists and, unconventionally, farmers and pigeon fanciers, then ran my own selective-breeding experiments and a worldwide correspondence network.

In my 1861–62 orchid research I used natural selection to make a testable prediction: a Madagascar orchid with a sixteen-inch nectary implied an unseen moth with a proboscis long enough to drain it.

From 1846 I dissected and classified the barnacles from my voyage, producing the definitive work on the group. Using my theory I found homologies and tiny parasitic males, and in 1853 the research won the Royal Society's Royal Medal.

After Wallace's parallel work forced the issue, our theory was read at the Linnean Society on 1 July 1858. Thirteen months later I finished On the Origin of Species, whose 1,250 copies were oversubscribed on its first day of sale.