Wallace attributed less importance than Darwin to sexual selection. In his 1878 book "Tropical Nature and Other Essays", he wrote extensively about the coloration of animals and plants and proposed alternative explanations for a number of cases Darwin had attributed to sexual selection. He revisited the topic at length in his 1889 book "Darwinism". In 1890, he wrote a critical review in "Nature" of his friend Edward Bagnall Poulton's "The Colours of Animals" which supported Darwin on sexual selection, attacking especially Poulton's claims on the "aesthetic preferences of the insect world".