Scientific Legacy

By George Beccaloni, October 2017 (last updated January 2023)

Theories Devised by Wallace Which Have Withstood the Test of Time

Unlike Darwin, Wallace 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 (in his seminal 'Ternate Essay' of 1858) and he was therefore in fact (ironically), the first neo-Darwinian. Darwin, in contrast, believed that the inheritance of acquired characteristics operated alongside natural selection, and infamously even proposed a mechanism to explain it - his erroneous theory of Pangenesis. A strong case could be therefore made that Wallace was the first to propose a correct theory of adaptive evolution, since Darwin's 'hybrid' theory was flawed.

Wallace's contributions to science actually went far beyond 'merely' co-discovering the theory on which modern biology is based (evolution by natural selection). He 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. 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, Wallace was therefore more correct about the origin of species than Darwin was, inheritance of acquired characters aside! Wallace importantly, 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. Letters between Darwin and Wallace show that Darwin failed to grasp Wallace's theory. Darwin did not himself provide a mechanism which could explain the evolution of reproductive isolation.

Interestingly, although many think of sexual selection as being Darwin’s theory, Wallace's ‘good genes’ argument (Wallacean Sexual Selection) 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. Wallace could never accept that ‘simple’ animals such as butterflies have an appreciation of beauty. He was always "more Darwinian than Darwin" in believing that evolution is a result of natural selection alone.

Wallace made many other major contributions to our understanding of animal colouration as well. He devised the concept of warning colouration (aposematism) in animals (e.g. where caterpillars have evolved conspicuous colours to advertise their toxicity to potential predators); he was the first to propose how cryptic colouration (camouflage) in animals evolved; he proposed the concepts of luring colours, deflection markings and disruptive colouration; he devised the theory of recognition marks in animals (a study on facial patterns of monkeys recently gave support to this theory); and he also proposed a theory to explain sexual dimorphism in animals. He was the first to suggest mimicry in birdssnakes and Pachyrhynchini weevils; he discovered polymorphic sex-limited mimicry in butterflies; he proposed what is known as the morphological defence hypothesis to explain how the extremely hard exoskeletons of certain weevils have evolved to make them 'unprofitable prey' for potential predators; he also proposed that other beetles have evolved to mimic these weevils to benefit from the weevil's defence. He also was the first to suggest that the brilliantly-coloured fishes from warm seas are in fact "well concealed when surrounded by the brilliant sea-weeds, corals, sea-anemones, and other marine animals, which make the sea-bottom sometimes resemble a fantastic flower-garden”. In 1868 he proposed that natural rather than sexual selection could explain the striking differences in avian plumage dichromatism. Thus, he predicted that nesting habits, through their association with nest predation, could drive changes in sexual dichromatism by enabling females in cavity nesters to become as conspicuous as males. His hypothesis has recently been tested and it received some support. He also produced the first functional classification of animal colours.

In the field of evolutionary biogeography (a discipline he is regarded as being the 'father' of), Wallace not only discovered the famous Wallace Line, but his map of the World's Zoogeographical Regions has stood the test of time remarkably well. Wallace was a pioneer of the study of latitudinal gradients in species richness. In his 1878 book Tropical Nature, and Other Essays he attributed the greater diversity of the tropics to the greater age of tropical regions and their having escaped the catastrophic extinctions caused by glacial climates at higher latitudes. This is now known as the 'Species-Time Hypothesis'. He also originated what was later called the "Pleistocene pump hypothesis" of speciation in his 1880 book Island Life. He believed that the repetition of glacial and warm periods promoted the spread and subsequent isolation of populations, hence promoting speciation. His earliest biogeographical theory, known as the riverine barrier hypothesis, is still a topic of research today. His many other important contributions to evolutionary biogeography are discussed by Heaney in his Introduction to a reprinted edition of Wallace's book Island Life (see HERE).

Another of Wallace's ideas was 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. He also devised the first evolutionary theory to explain aging and death (now known as the Wallace-Weismann hypothesis); he was the first biologist to seriously attempt to evaluate the likelihood of life on other planets; and he was an important pioneer of statistical epidemiology. In addition he was the first Westerner to observe and document the spectacular mating displays (leks) of male Birds of Paradise; the first person to point out that the average size of beetles is no greater in the tropics than in temperate regions; and perhaps the first to argue that flightless ratites evolved several times, independently, from a flying ancestor.

How Wallace is Regarded Today

In most biographies I have read about Darwin, Wallace is only briefly mentioned, which seems extraordinary given that the publication of natural selection with Wallace, was such a notable and dramatic event in Darwin's life. One would think that the full story of how the two men came to publish the theory together would be documented in detail, but this is not the case. [My detailed account can be read HERE]  Also missing are details of their ongoing friendly relationship, both personal and professional. They often discussed their theoretical ideas together, and did not always agree. Wallace became a very vocal defender of their joint theory, yet it is usually Thomas Huxley who is mentioned as filling this role, even though, as Wallace and Darwin scholar Jim Costa has pointed out "Wallace out-Huxleyed Huxley" in this regard!

In literature about Darwin' life and work, I have seen some authors trying to diminish Wallace's discovery of natural selection by trying to argue that because Darwin discovered the theory 20 years before Wallace, he deserves more credit. This is not, however, the way that credit is apportioned for scientific discoveries: discoverers are only credited once they publish their work, and in cases of multiple authorship the credit is divided equally between the co-authors. So, given that Darwin and Wallace simultaneously published their identical theories of natural selection in their 'joint paper' of August 1858, credit for the idea should be equally shared between them. It is interesting to note that Wallace had been actively searching for a mechanism to explain adaptive evolutionary change for 10 years before he discovered natural selection in February 1858. He had specifically gone to Brazil with Henry Bates in 1848, to investigate evolution, and although he made little progress there, he made rapid strides during his trip to the Malay Archipelago which began in 1854. In 1855 he published his notable "Sarawak Law" essay, which argued on the basis of several lines of evidence, that evolution was the true explaination of life's diversity, and this was followed by several other significant articles, all of which were written in the field, often under difficult conditions. He was even making notes for a book on evolution, which he later abandoned when Darwin's Origin of Species was published in 1859 (see HERE).

Another ploy which authors use to give Darwin more credit for the theory, is to say that the 1858 paper was largely ignored, and it was only with the publication of Origin of Species, 15 months later, that the theory was brought before scholars and the public. That the paper was largely ignored is, however, incorrect, a fact I hope to demonstrate in a paper I am currently working on. Even if this had been the case, it doesn't alter the fact that Darwin and Wallace were co-discoverers of natural selection.  

Others point out that Wallace always gave Darwin the bulk of the credit for the discovery, even naming his 1889 book on evolution Darwinism. Although that was certainly true and very generous of Wallace, it again cannot alter the fact that his and Darwin's ideas were published jointly, so they should receive equal credit.

One final tactic used to attempt to diminish Wallace in the eyes of readers, is to point out that he was a spiritualist. However, not only was Wallace an atheist when he discovered natural selection (he only became a convert to spiritualism in his 40s after his return from the Malay Archipelago), Darwin was actually a Christian when he first conceived the theory! In any case, such beliefs are irrelevant to the issue of credit, as they do not alter the fact that both men co-authored the theory.

Wallace became one of the most famous people in the World during his lifetime and was given numerous prestigious scientific awards for his work, including for his independent discovery of natural selection (for which he received five medals). He was highly thought of by his contemporaries, Darwin and Huxley included, and his spiritualism and stance against compulsory vaccination did not seriously damage his reputation, despite what later biographers might say.

This short obituary of Wallace in Nature, 13 November 1913, just 6 days after his death, gives a good concise summary of his work and indicates how highly regarded his work was by his contemporaries. There has not been another biologist who has made such a multitude of important contributions to evolutionary biology as Wallace.

DR. ALFRED RUSSEL WALLACE, O.M., F.R.S.

THE death of Alfred Russel Wallace on November 7, at ninety years of age, marks a milestone in the history of biology. For he was the last distinguished representative of a type that can never be again - a combination of naturalist-traveller, biologist, and geographer, a knower of species, and yet from first to last a generaliser "inquisitive about causes," and, with all this an investigator who stood outside any of the usual methods of analysis, with "a positive distaste for all forms of anatomical and physiological experiment." It will probably be a very long time before a biologist again rises to real distinction apart from experimental analysis in some form or other. His career and scientific work were described in these columns by Prof. H. F. Osborn in June of last year (vol. lxxxix., p. 367 [Click HERE]), and we hope to publish a further appreciation of him next week. Here, therefore, we do little more than record his death and point to some outstanding characteristics of his life.

In thinking of Wallace's contributions to science, we recall first the feverish week at Ternate, when he wrote his famous letter to Darwin, "like a thunderbolt from a cloudless sky," expounding the idea of natural selection - a letter which was communicated, along with extracts from Darwin's unpublished work, to the Linnean Society at the historical meeting on July 1, 1858. Everyone is proud of the magnanimity with which each discoverer treated the claims of the other. Their detachment from everything but getting at the truth was congruent with the nobility of both. It was indeed just what might have been expected, but there was throughout an instinctive generosity which has always appealed to the ethical imagination. Darwin's helpful friendliness was met by Wallace's devoted loyalty, which was conspicuous, for instance, when he gave his fine book of 1889 the title "Darwinism," or emphasised at the 1908 celebration the fact that the idea of natural selection had occurred to Darwin nearly twenty years before the joint paper of 1858. Well was it said of him, "Darwinii aemulum, immo Darwinium alterum."

After natural selection, one thinks of the geographical distribution of animals, and it may be justly said that this study, whlch has evolved vigorously in many directions in the last generation got its modern start from Wallace's standard work (1876), which fulfilled its intention of bearing to the eleventh and twelfth chapters of the "Origin of Species," a relation similar to that which "Animals and Plants under Domestication" bears to the first. It was followed up by the more popular "Island Life," which has been a stimulus to many a travelling naturalist, and has prompted numerous investigations.

The building up of a science often reminds one of the waves making a new beach - multitudes of particular movements which are not in themselves permanent, but make others of more lasting effect possible. Perhaps the same should be said of much that Wallace's fertile mind contributed, for instance, in regard to sexual selection, concerning which he was wisely sceptical, in regard to "warning colours" and "recognition marks," in regard to the part played by instruction and imitation in the development of instinctive behaviour; and many more instances might be given. As an old man he was impatient of the recent work which centres round Mendelism and mutations but it was a fine example of his earlier plasticity of mind that he entirely agreed with Weismann in finding the transmission of acquired characters unproved. His independence was conspicuously shown by the vigour with which he maintained in his "Darwinism" and elsewhere that the facts of man's higher nature compel us to postulate a special "spiritual influx," comparable to that which intervened, he thought, when living organisms first appeared and when consciousness began. He may have lacked philosophical discipline, but he was never awanting in the courage of his convictions. Throughout his life he was given to puzzling over difficult problems far beyond the range of biology - in economics and astronomy, in psychology and politics, and perhaps it was this width of interest in part that kept him young so long.

There was a great humanity about Alfred Russel Wallace, which won affection as surely as his services to science commanded respect. Like many hard workers he found time to be generously kind to young men; he did not suffer fools gladly, but he was always ready to champion the cause of the oppressed; he could never divest himself of his citizenship, and almost to his last breath he was thinking of how things might be made better in the State. By nature quiet, gentle, reflective, and religious, he had no ambitions save for truth and justice and the welfare of his fellow-men; he was satisfied with plain living and high thinking, with his garden, and with that "double vision" which was always with him. For, whatever we may think of his "spiritualism," it was peculiarly his

To see the world in a grain of sand,
And heaven in a flower;
To grasp infinity in the palm of the hand
And eternity in an hour.

To see many more obituaries of Wallace click HERE

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