A S
Can you explain the significance of this?  

G B
Well, there aren’t discrete morphs among humans. We’re mixtures of our parents; whereas with butterflies, there’s one kind of male with, say, black wings, and then five different female color patterns, each of which has evolved to look like a different species of poisonous butterfly. When they breed, you always get the same males and this array of different female patterns. That’s why it is called sexlimited polymorphic mimicry. Wallace discovered this in the Southeast Asian swallowtail butterfly, Papilio memnon, but it became more famous when something similar was discovered in another swallowtail species called Papilio dardanus in Africa. It was then studied for a hundred years and still, to this day, researchers are trying to work out how the different mimetic morphs actually arose, and the genetics of the process. Wallace must have gotten a batch of eggs, reared the caterpillars, and saw that they produced black males and five different types of females; he realized that all these females he thought were different were actually of the same species.

A S
Didn’t Wallace reject Darwin’s theory of sexual selection?

G B
Interestingly, the modern theory of sexual selection actually has more to do with Wallace’s ideas than Darwin’s. Everyone says that Darwin came up with the theory of sexual selection and Wallace rejected it, but if they knew enough about the modern theory, it’s actually quite the reverse!

A S
Can you explain more about these two theories?

G B
Darwin’s theory says that the females of a species have an appreciation of beauty and that they pick the most beautiful males to mate with because they deemed them to be beautiful. Wallace couldn’t imagine that a butterfly would have an aesthetic sense. Why would a tiny insect brain be able to judge beauty in this way? He couldn’t understand how female butterflies could choose more beautiful males, so he argued against Darwin’s idea, which suggested in essence that these creatures knew what beauty was and chose it for its own sake. Wallace’s idea was that the plumage, for example, had some other function. It was basically the most vigorous males who were able to produce the best plumage, which was a sign of vigor and health. So, by choosing the best plumage the females were choosing the healthiest males. Or, in the case of antelopes, say, it would be the males with the biggest horns who were chosen by the females because they knew their offspring would have those characteristics. That’s what the modern theory of sexual selection is all about, which follows from Wallace’s “better genes” argument for selection, as opposed to the aesthetic sense idea from Darwin. In sexual selection, for Wallace, beauty is an index or register of health and vigor, not an aesthetic quality chosen for its own sake.

A S
Continuing from here, can you summarize what distinguishes Wallace from his contemporaries? Why is he so special in the history of science?

G B
He came from a poor family and was largely self-educated, yet he achieved really great things. When people think of Wallace—if they think of him at all—they think of the Wallace Line, or maybe even the co-discovery of natural selection, but his legacy goes far beyond that. His contributions to biology are very important, much more so than most of the other people in his day, such as Joseph Hooker or T. H. Huxley, even. Only Darwin made similar contributions. Let me read you something I recently wrote on this:

“Wallace’s contributions to biology went far beyond merely co-discovering the theory on which the modern science is based. Unlike Darwin, he always rejected Lamarckism—the inheritance of characteristics acquired during the life of a parent, like 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, ironically, the first neo-Darwinian. Wallace devised the first modern definition of what species are—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, by 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! Interestingly, although many think of sexual selection as being Darwin’s theory, Wallace’s ‘good genes’argument to explain the evolution of sexual characteristics is regarded by many scientists today as more plausiblethan Darwin’s belief that females choose mates on aesthetic grounds. Even the concept of warning coloration in animals (e.g. where caterpillars have evolved conspicuous colors toadvertise 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 thetwo previously isolated continents werejoined together by the formation ofthe Isthmus of Panama about three million years ago) were theories originally conceived by Wallace.”³

There are other things, too, like recognitionmarks in animals; a scientificpaper about facial patterns in monkeysrecently confirmed Wallace’s theoryof recognition marks. He was also thefounder of astrobiology; he came upwith the first plausible evolutionaryidea of aging and death; he was first topropose mimicry in birds and in snakes,and mimetic polymorphism in butterflies.Then there was the Wallace Line,of course, and the fact that he collectedabout 19,000 species new to sciencein the Malay Archipelago.

A S
Can you explain more about he Biological Species Concept? Wasn’t that Ernst Mayr’s idea?

G B
People often believe that Mayr cameup with the Biological Species Concept,but he actually took it from Wallace,who was the first to claim that speciesshould be defined as interbreedinggroups that are reproductively isolatedfrom other such groups. Incidentally,there’s nothing in On the Origin of Species that actually explains whata species is. So, even though it’s a bookabout their origin, Darwin neverdefines what he means by species.

A S
Do you think there is a way that the study of Wallace could contribute to the current discussion of the Anthropocene?

G B
I’m not sure, but I think it should be called the Destructocene.