MYTH 12

THAT WALLACE’S AND DARWIN’S EXPLANATIONS OF EVOLUTION WERE VIRTUALLY THE SAME

Michael Ruse

Wallace set forth clearly the same theory as Darwin’s, which he had conceived independently, that species of animals have evolved from each other through the action of natural selection.

—George Ledyard Stebbins, Processes of Organic Evolution (1971)

You said this when I explained to you here very briefly my views of “Natural Selection” depending on the Struggle for existence.—I never saw a more striking coincidence. If Wallace had my M.S. sketch written out in 1842 he could not have made a better short abstract. Even his terms now stand as Heads of my Chapters.

—C. R. Darwin to Charles Lyell (June 18, 1858)

Let’s start with undeniable facts. Charles Darwin (1809–1882) and Alfred Russel Wallace (1823–1913) both became evolutionists; they both discovered natural selection, even though it was Darwin who alone used this term until Wallace urged on him Herbert Spencer’s (1820–1903) alternative “survival of the fittest”; they both saw Thomas Robert Malthus (1766–1834) as a key influence in their discovery; and they both saw adaptation to circumstances as a crucial part of the process/product of evolution. Oh, yes—and the two made their discoveries independently.

There is a good reason why the names of Darwin and Wallace are linked. There is also a good reason why the revolution is “Darwinian” and not “Wallacean.” Apart from the fact that Darwin got there twenty years before Wallace, from the very beginning (the Sketch of 1842) Darwin had a full theory in mind, covering a Whewellian “consilience of inductions” from social behavior, paleontology, biogeography, systematics, morphology, and embryology. Although Wallace was to do seminal work in such areas as biogeography, this was only done later. It is not there at the end of the 1850s, when Darwin and Wallace first published.1

This said, we have all known that there were differences, and I must say that rereading Wallace’s 1858 essay (the one he sent to Darwin) for the first time in several years, I am struck by how great are the differences. I am not into counterfactual history with the enthusiasm of Peter Bowler, and I feel sure that today we would have something along the lines of the theory of evolution that we do have today—apart from anything else, it is true—but I see history with a Wallace and no Darwin as being a bit different, starting with the fact that Wallace might have had trouble getting his paper published and noticed.²

The most obvious difference between Darwin and Wallace—one that people universally comment on—is that whereas the domestic world and artificial selection are a fundamental part of Darwin’s theory, not only are they not part of Wallace’s theory but he goes to some considerable effort to deny their relevance. Wallace agrees with general opinion that domestic change is never permanent, and so he must show that it is unlike natural change. This he does by suggesting that domestic changes, like shorter legs or fatter bodies, would always be deleterious in the wild and so could never persist. Hence, domestic changes in some inherent way are different from natural changes.

In my youth, trained as a philosopher in the logical empiricist tradition, I would have argued happily that none of this is very significant. I would have argued that the domestic world was not really an essential part of Darwin’s argument—which begins only with Malthus and the struggle for existence—and so the talk of the farmyard and the breeders’ clubs could be sloughed off. Darwin and Wallace are back together again. Forty years of doing the history of science has convinced me that this will not do. The domestic world is in the Origin (and the earlier versions) just as much as embryology is, and sauce for the gosling (as one might say) is sauce for the goose and gander.

We know why the domestic world is in Darwin’s theory.3 Unlike everyone else, Darwin had a rural background and knew of the great advances that had been made by breeders in the previous half century or so. His uncle Josiah Wedgwood II (1769–1843)—the father of his wife, Emma (1808–1896)—was a gentleman farmer, much into trials with artificial selection. Darwin knew how effective induced change could be. Also, Darwin was (certainly compared to Wallace) far more methodologically sophisticated. Artificial selection gave him the handle to an empiricist vera causa backing for natural selection—a demand that figured greatly in the thinking of Darwin’s intellectual mentor John F. W. Herschel (1792–1871).⁴ Artificial selection was a force produced by human will that made plausible the analogous force of natural selection, something we cannot experience directly (or so Darwin thought).

I would today take matters further. Artificial selection is inherently bound up with the metaphor of design. Darwin quoted the breeder John Sebright (1767–1846) on this. You decide the kind of animal or plant you want and then you set about producing it. Likewise, natural selection is speaking to design—the functioning of adapted organisms, as picked up by the natural theologians, such as William Paley (1743–1805), and used as proof of the existence of God (see Myth 8). I am not now interested in whether Darwin was likewise theologically concerned (early he did think there was proof, later he went the other way); I am not now interested in whether my good friend Robert J. Richards is right in thinking this points to the neo-Naturphilosoph Darwin seeing life forces pervading nature (he didn’t, and Richards is wrong); and I am not now interested in whether Stephen J. Gould (1941–2002) was right in thinking that this led Darwin into undue adaptationism (it didn’t). I am concerned in stressing that you can’t drop metaphors—I really have gone beyond logical empiricism!—and that this metaphor of selection leading to design is an inherent part of Darwin’s theory in a way that it is not for Wallace.

It is true that Wallace (in his 1858 essay) acknowledges adaptation and its importance, and later (in the 1860s), under the influence of Darwin, he does important work on the adaptations of butterflies and moths; but in the essay I just don’t see the design intoxication that we find in Darwin, from the first jottings to the Origin (and later). Wallace sees adaptation as important for success, but he is not using design to peer into the very nature of organisms, as does Darwin. To use Aristotelian categories, there is something deeply teleological about Darwin’s thinking that I don’t sense in Wallace. Final cause is also at issue. For Wallace, one bird flies better than another simply because it has stronger wings—there is something sadly ironic that his example of a success is that of the passenger pigeon—whereas for Darwin, the better wings exist to fly faster. In the end, of course—pace Richards—they are both mechanists (this is all before Wallace became a spiritualist), but at the very least, Darwin has a heuristic tool that Wallace does not have: a way to look for adaptation in a way that Wallace doesn’t.5

So much for the domestic-world analogy; I’ll come back to it at the end. I want to turn now to something that Peter Bowler spotted some thirty years ago.⁶ Both Darwin and Wallace realize that the Malthusian struggle takes place among individuals. One bird flies faster than another and thus escapes the predator. For Darwin, this is fundamental. Change starts (and I would say ends) here. “Hence, as more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life.”7 For Wallace, however, the individual struggle seems more of a purifying process within the group. If you are second rate, you are going to get wiped out. Change is a group phenomenon. One variety is going to do better than another. The very title of Wallace’s essay flags the reader to this: “On the tendency of varieties to depart indefinitely from the original type.” More than just this, the change doesn’t seem to come about because one variety goes to war with another variety and wins—at least not directly. It is all a matter of change of circumstances and of one variety doing better in the new circumstances than do other varieties. So if you have a new variety within a species and circumstances change and the new variety does better than the mother species, the mother species gets eliminated and change has occurred. This is very different from Darwin’s picture, in which change can certainly occur because of a change of circumstances—a new predator, for instance—but can also occur internal to the group, like when one form uses a little less food than the others.

In a way, therefore, I see Wallace as being more passive than the active Darwin. For Wallace, you wait for the world to impose change. For Darwin, you can start the change yourself. I am not sure if this has any linkup with Darwin’s acceptance of the inheritance of acquired traits (so-called “Lamarckism”) and Wallace’s rejection thereof—another difference, and obviously here one that posterity judges Wallace right and Darwin wrong (see Myth 10). More significantly, I see this as a clear mark of another difference that always existed between Darwin and Wallace. Darwin, the child (particularly the grandchild) of industrialists, always bought into the Adam Smith (1723–1790) philosophy—that is, nobody does anything for anybody else without a hope of return. “It is not from the benevolence of the butcher, the brewer, or the baker that we expect our dinner, but from their regard to their own interest.”⁸ He was, in today’s lingo, ever an individual selectionist. Wallace, the man who first heard the socialist Robert Owen (1771–1858) as a young teenager and who at the end of his life said that Owen was one of his greatest influences, was ever a group selectionist. For Darwin, it is always one organism against all others—allowing that the Darwin-Wedgwood-embedded Darwin (he married his own cousin, as did his sister, and remained cocooned at Down after he became sick) considered the family to be part of self. For Wallace, it was always one group sticking together and going through life pressured by the outside world. It is worth noting that Darwin and Wallace became very much aware of their differences on this matter and in the 1860s argued the topic fully without either budging the other.9

At this point I join together the difference over the domestic world and the difference over the focus of change, individual or group. From the beginning, Darwin had a secondary mechanism—sexual selection—and this he divided into male combat and female choice (see Myth 14). It is obviously an idea that comes from the domestic world, where we have selection for food and other useful attributes and selection for our sport and amusement, and where the latter generally comes in one of two forms: fighting animals (usually males) and beautiful animals (again often males). Up to and including the Origin, sexual selection was really secondary, but with Darwin, it became incredibly important. Shocked by Wallace’s apostasy, arguing that humans could not have been created naturally, but agreeing that Wallace was right that many features (such as hairlessness) cannot be explained by natural selection, Darwin turned to sexual selection for support, and this mechanism became a major topic and tool in The Descent of Man (1871).¹⁰

Wallace expectedly had nothing on sexual selection in his 1858 essay, and then, although he accepted sexual selection through male combat, quickly rejected sexual selection through female choice, arguing that the reason why males are often gaudy and females rather drab has nothing to do with choice and everything to do with camouflage. Females sitting passively with their eggs or young needed to escape detection, and so they evolved colors accordingly.¹¹

I need hardly say that sexual selection is the epitome of individual selection. It takes place only among members of the same species, and for sure no one is doing anything for anyone else. It is quintessentially Darwinian. I don’t know that Wallace rejected sexual selection because it was individualistic—he always accepted male combat—but he had no urge to go that way, and the drab-females hypothesis does rather fit into his picture of change coming to varieties because of outside pressures.

Of course Darwin and Wallace had the same theory, but when you start to dig into things, beneath the surface their theories were not quite as similar as most people assume.