Alfred Russel Wallace : biography
Defence of Darwin and his ideas
After the publication of Darwin’s On the Origin of Species, Wallace became one of its staunchest defenders on his return to England in 1862. In one incident in 1863 that particularly pleased Darwin, Wallace published the short paper "Remarks on the Rev. S. Haughton’s Paper on the Bee’s Cell, And on the Origin of Species" in order to rebuke a paper by a professor of geology at the University of Dublin that had sharply criticised Darwin’s comments in the Origin on how hexagonal honey bee cells could have evolved through natural selection.Slotten pp. 197–99.
An even lengthier defence of Darwin’s work was "Creation by Law", a review Wallace wrote in 1867 for The Quarterly Journal of Science of the book The Reign of Law, which had been written by George Campbell, the 8th Duke of Argyll, as a refutation of natural selection. After an 1870 meeting of the British Association, Wallace wrote to Darwin complaining that there were "no opponents left who know anything of natural history, so that there are none of the good discussions we used to have."Slotten p. 261.
Differences between Darwin’s and Wallace’s ideas on natural selection
Historians of science have noted that, while Darwin considered the ideas in Wallace’s paper to be essentially the same as his own, there were differences. Darwin emphasised competition between individuals of the same species to survive and reproduce, whereas Wallace emphasised environmental pressures on varieties and species forcing them to become adapted to their local environment.Larson p. 75.Bowler & Morus p. 149.
Others have noted that another difference was that Wallace appeared to have envisioned natural selection as a kind of feedback mechanism keeping species and varieties adapted to their environment. They point to a largely overlooked passage of Wallace’s famous 1858 paper:
The action of this principle is exactly like that of the centrifugal governor of the steam engine, which checks and corrects any irregularities almost before they become evident; and in like manner no unbalanced deficiency in the animal kingdom can ever reach any conspicuous magnitude, because it would make itself felt at the very first step, by rendering existence difficult and extinction almost sure soon to follow.
The cybernetician and anthropologist Gregory Bateson would observe in the 1970s that, though writing it only as an example, Wallace had "probably said the most powerful thing that’d been said in the 19th Century". Bateson revisited the topic in his 1979 book Mind and Nature: A Necessary Unity, and other scholars have continued to explore the connection between natural selection and systems theory.
Warning colouration and sexual selection
In 1867, Darwin wrote to Wallace about a problem he was having understanding how some caterpillars could have evolved conspicuous colour schemes. Darwin had come to believe that sexual selection, an agency to which Wallace did not attribute the same importance as Darwin did, explained many conspicuous animal colour schemes. However, Darwin realised that this could not apply to caterpillars. Wallace responded that he and Henry Bates had observed that many of the most spectacular butterflies had a peculiar odour and taste, and that he had been told by John Jenner Weir that birds would not eat a certain kind of common white moth because they found it unpalatable. "Now, as the white moth is as conspicuous at dusk as a coloured caterpillar in the daylight", Wallace wrote back to Darwin that it seemed likely that the conspicuous colour scheme served as a warning to predators and thus could have evolved through natural selection. Darwin was impressed by the idea. At a subsequent meeting of the Entomological Society, Wallace asked for any evidence anyone might have on the topic. In 1869, Weir published data from experiments and observations involving brightly coloured caterpillars that supported Wallace’s idea. Warning colouration was one of a number of contributions Wallace made in the area of the evolution of animal colouration in general and the concept of protective colouration in particular.Slotten pp. 251–54. It was also part of a lifelong disagreement Wallace had with Darwin over the importance of sexual selection. In his 1878 book Tropical Nature and Other Essays, he wrote extensively on the colouration of animals and plants and proposed alternative explanations for a number of cases Darwin had attributed to sexual selection.Slotten pp. 353–56. 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 "æsthetic preferences of the insect world".