By George Beccaloni, October 2017
Wallace's contributions to science went far beyond merely co-discovering the theory on which modern biology is based. Unlike Darwin, he always rejected Lamarckism - the inheritance of characteristics acquired during the life of a parent (for example the enlarged biceps developed by a blacksmith over the course of his career). In fact he was the first natural selectionist to reject this flawed theory and he was therefore in fact, ironically, the first neo-Darwinian. ARW devised the first modern definition of what a species is - a slightly modified version of which would later become known as the Biological Species Concept; in addition he believed that speciation typically occurs in allopatry or parapatry - when diverging populations are geographically separated or abutting. He also proposed what is known as the Wallace Effect (also called Reinforcement) to explain how natural selection against hybrids between incipient species could contribute to reproductive isolation and hence speciation. Darwin in contrast believed that speciation occurs largely as a result of competition in sympatry (within the same habitat) - a theory he called his Principle of Divergence. Given that it is now thought that most speciation is a consequence of geographical isolation, ARW was therefore more correct about the origin of species than Darwin was! Interestingly, although many think of sexual selection as being Darwin’s theory, ARW’s ‘good genes’ argument to explain the evolution of sexual characteristics (i.e. that females select males seen to have genetic advantages that increase offspring quality) is regarded by many scientists today as more plausible than Darwin’s belief that females choose mates on aesthetic grounds, simply because they are more beautiful. ARW could never accept that ‘simple’ animals such as butterflies could have an appreciation of beauty. Even the concept of warning colouration in animals (e.g. where caterpillars have evolved conspicuous colours to advertise their toxicity to potential predators) and the idea of the Great American Interchange (where animals from South America moved into North America and vice versa, when the two previously isolated continents were joined together by the formation of the Isthmus of Panama about three million years ago) were originally conceived by Wallace.
In addition, Wallace was the first to propose how cryptic colouration (camouflage) in animals evolved; he proposed the theory of recognition marks in animals; he produced the first functional classification of animal colours;
And, of course, his pioneering work on evolutionary biogeography led to him becoming recognised as that subject’s founder.
The above is an incomplete summary, more will be added in future.