In
Darwinism fifteen chapters,
Alfred Russel Wallace sets out his understanding of the theory of
evolution by
natural selection. He begins by defining "
species", discussing
creationism, opinion before
Charles Darwin, and Darwin's theory. He then describes the
Malthusian struggle for existence, given the ability of organisms to reproduce in a world of finite resources. He explains the importance of variability within species, giving examples. He describes variation in domesticated animals and cultivated plants, and the process of
artificial selection by breeders. Wallace then explains the process of natural selection acting on pre-existing variation. He lists various issues and objections to the theory. He discusses how
interspecies hybrids are usually infertile, and how this can contribute to reproductive isolation. He then examines the purpose of
animal coloration, including
camouflage and
mimicry, arguing that these are
evidence of natural selection. He gives detailed examples of
warning coloration and mimicry, discussing how these are produced by selection. Animal coloration and ornamentation that differs between the sexes are discussed, though he largely disagrees with Darwin's theory of
sexual selection. Wallace then explores the co-evolution of flowers with their pollinators including insects and birds. He then describes the
geographical distribution of organisms, arguing that this was created by long-distance dispersal of pioneer organisms, such as insects blown across the sea. He explains the geological evidence for evolution, the
fossil record in successive layers of rock. He then examines objections to Darwinism concerning variation and heredity. Finally, he looks at how Darwinism may apply to humans. File:Darwinism 1889 page 219.jpg|Wallace discusses the purposes of herbivore coloration as danger and recognition
signals, with an illustration of
Soemmerring's gazelle. File:Darwinism 1889 page 259 image of mimicry.jpg|Wallace discusses
Batesian mimicry with a plate of
a beetle that closely mimics a wasp. File:Darwinism 1889 page 320 flowers adapted for bird pollination.jpg|Wallace discusses the
coevolution of flowers and pollinators, illustrating it with a
bird-pollinated flower. == Analysis ==