Alfred Russel Wallace and Charles Darwin
Alfred Russel Wallace (8 January 1823–7 November 1913) and Charles Darwin (12 February 1809–19 April 1882) are jointly credited with contributing the doctrine of natural selection to the scientific literature. There can be no doubt that they independently conceived of the same theory; the priority question was settled amicably by a joint publication in 1858.
Darwin has become, with considerable justification, the flag-bearer of evolution, but many of his (near-)contemporaries poured over the same questions. The obverse side of hero worship is indignation over those who were overlooked: the perniciousness of Darwinists allegedly shown by the manner in which Wallace, a formidable biogeographical scientist in his own right, was robbed of the priority credit. However, history and human relationships can be, and thankfully often are, more subtle than squabbles over priority. In reality, Darwin’s response was admirably honorable, and the real interest resides in appreciating both men’s contributions against the backdrop of contemporary views on varieties in nature.
Affinity and mutability: the origins of an idea
Evolution, as phenomenon, is the corpus of observations attesting to the fact that life on earth has not always been the same. Over the course of mega-anni, ecosystems and the species that inhabit them have changed, often and dramatically. Evolution, as theory, is any account seeking to explain these facts, including contrarian accounts that attempt to explain the facts away, that is, to repudiate the measurement of the deep time scale, or the sweeping nature of the changes, or both. Or, spurred by an urge to reconcile respect for scientific observation with religious piety, one might countenance a theory of intelligent redesign, in which the creator continually revises and recreates.
The philosophical landscape was quite different in the time of Darwin and Wallace. The nature and media of the changes observed took center stage. Mendelian genetics was being developed at the time, but would not be widely recognized until the turn of the century (Fisher 1936) – and molecular genetics lay even further in the future. Even if such gaps in contemporary knowledge seem all but fatal handicaps to us, we should examine without prejudice the development of evolutionary thought against the intellectual backdrop of the time.
The similarity or “affinity” that exists between parent and child, raven and crow, perhaps even shark and tiger, or octopus and jellyfish, must always have been evident to naturalists. But what were they to make of this affinity, and how could it allow one life form to pass into the other?
The idea of inheritance of acquired characteristics, previously widely accepted, had begun to fall by the wayside. This doctrine, traditionally associated with Jean-Baptiste Lamarck (1744–1829), who certainly gave it a crisp wording (Lamarck 1809), presupposes that the next generation may somehow be imprinted with the striving of the parents. We observe adaptive changes through the course of an individual’s lifetime, e.g., hypertrophy of muscles under strain, or learning – and we also observe adaptive changes over the course of generations. It is natural to suppose that similar mechanisms are at work and that, consequently, adaptive changes can be passed on through gamete or spore. In Lamarck’s thought this was wedded to the concept of an inherent force striving toward greater complexity; whereas Darwin imagined a neat mechanism for the inheritance of acquired characteristics, whereby each organ or tissue brings forth a microscopic representative “avatar” that contributes to the gamete (stretching this idea perhaps beyond its limit, we may here vaguely discern the outlines of modern epigenetics), Wallace roundly considered the experiments refuting Lamarckism to have settled the question, which, in any case, he felt was rendered moot by the operation of natural selection.
The ineffable affinity that ties living beings together finds a striking expression in Genesis 1:26: “God said, Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing.” If man is made in God’s likeness, then the stuff that life is made of (muscles, sinews, blood, etc.) must be present in the human body in perfect proportion and harmony. Moreover, such perfection must be lacking in all other live forms, in increasing degree as we descend a hierarchy known as the great chain of being. One could view all nonhuman beings as lacking in reason, for instance, or regard the Mollusca as being out of proportion, relative to the divine formula of man, in being mostly composed of muscle. Thus we account for both the affinity and diversity of life and even have a rudimentary form of genetics in which species are defined by a divinely ordained “formula of (dis)harmony/(dis)proportion.”
This point of view severely constrains the definition and malleability of species and forbids transmutation, the ability of species to evolve into one another. We concur with Darwin that it is “absurd to talk of one animal being higher than another,” but if we momentarily allow that life is ordered hierarchically, we should applaud Lamarck for his boldness in proposing that life strives to move up this ladder. Going against such radical ideas, prima facie evidence for an immutable, ingrained (and Divinely ordained) “formula” was seen in the tendency for domestic animals, when released into the wild, to “revert to type,” that is, while breeding in captivity may have stretched the makeup of the beasts away from the divine formula, when left to its own devices, the species springs back, or regresses, to its true inborn form. Varieties may temporarily depart from the original type, but not forever, nor without bound.
It is precisely this doctrine that Wallace seeks to refute in his essay “On the Tendency of Varieties to Depart Indefinitely From the Original Type” where he argues that the apparent “regression” of domesticated animals gone feral can be explained precisely because the harsh conditions of the natural environment that produced “the original type” must again give rise to something quite like it. But as these challenges change, so will the way the species respond to them, free to wander away arbitrarily far in morphogenetic space.
It seems uncanny to modern eyes that Wallace is talking so eloquently about natural selection without ever using these words; but that is just the terminology that was introduced with Darwin. Wallace’s thinking is clearly along the familiar lines of linking the lifetime reproductive success of an individual to its ability to, first, survive through to these reproductive events and, second, amass the resources that are to be invested in offspring. He cites the stock examples of characteristics such as camouflage, strong thigh muscles, and sharp claws as the sort of traits that aid the organism in achieving this success. He observes that, were nature to provide for every zygote to grow into an adult, the biomass of every species would grow exponentially – a manifest absurdity on a finite planet, which explains why selective pressure is huge.
One may well imagine Darwin’s consternation when Wallace sent him his essay in March of 1858: “If Wallace had my MS. sketch written out in 1842, he could not have made a better short abstract.” Darwin offered to help Wallace publishing his views. Moreover, Darwin had previously communicated writings on his ideas, which would allow him to “prove that I take nothing from Wallace. I should be extremely glad now to publish a sketch of my general views in about a dozen pages or so. But I cannot persuade myself that I can do so honourably… I would far rather burn my whole book than that he or any man should think that I had behaved in a paltry spirit” (Darwin 1958).
A compromise was found, and Wallace’s essay was published along with an extract from Darwin’s essay of 1844 (Darwin and Wallace 1858). Darwin’s “Origin of Species,” on which he had been working since the mid-1850s, was published a year later (Darwin 1858). Darwin’s ideas on evolution had first crystallized during his voyage on the Beagle in the 1830s and had been maturing ever since (Darwin 1958).
The wealth of case studies, the breadth of knowledge of natural history and biogeography, as well as its thoughtful style of argumentation made “Origin” the standard-bearer for evolution. The primary obstacle it overcame during its day was the doctrine of immutability, which was abandoned in favor of ongoing speciation and common descent.
Against a background of pre-Mendelian genetics, rejection of the transmutation of species for traditionalist-religious reasons, and expeditions yielding a wealth of biogeographical data, Wallace formulated the mechanism of natural selection independently of Darwin, who recognized Wallace’s insights as essentially identical to his own and shared the credit, in what effectively amounted to a preview publication of his “Origin of Species.”
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