On 16 September 1835 the British survey ship HMS Beagle made landfall on the Galapagos, a group of volcanic islands in the Pacific scattered like so many heaps of cinder on either side of the equator. On board was a 26-year-old English naturalist named Charles Darwin. The gruelling five-year expedition had given the young Darwin every opportunity to indulge his passion for exploring, observing and collecting specimens. He had already seen much that had impressed him deeply, yet he was still filled with awe by the unique geology, flora and fauna of the Galapagos, whose wonders included ground finches and mockingbirds, seaweed-eating iguanas, and giant tortoises.
The inspiration Darwin derived from these extraordinary encounters, on the Galapagos and elsewhere, helped him to formulate a theory that offered a compelling solution to what remained to most biologists the ‘mystery of mysteries’: the origin of the innumerable species of life on earth and an explanation of its astonishing diversity. Darwin’s theory of evolution by natural selection has since established itself as the cornerstone and unifying principle of the biological sciences. And its significance extends far beyond the confines of science. No other scientific theory has forced humans to make so radical a reappraisal of their own position in the world and their relationship to other living things.
The origin of species When the Beagle entered Falmouth harbour on 2 October 1836, the young naturalist on board, weighed down by thousands of specimens and reams of notes, was beset by many riddles prompted by his journey. Again and again, he had been brought face to face with the wondrous beauty and dreadful brutality of nature – not least of human nature. All he had seen helped to reinforce his sense of the impermanence of the environment and of the vast time scales over which the seemingly unchanging features of the earth had come and gone. Yet, in spite of the awesome scale of the undertaking, within a year of his return Darwin had begun to formulate the ideas that would eventually define his theory of evolution.
‘I am almost convinced … that species are not (it is like confessing a murder) immutable … I think I have found out (here’s presumption!) the simple way by which species become exquisitely adapted to various ends.’
Charles Darwin, letter to J.D. Hooker, 1844
It was more than two decades, however, before Darwin would publish (in 1859) the classic statement of the theory: the momentous On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. The long delay has usually been attributed to the author’s anxieties about the public reception that would greet his ideas. It is true that the orthodox scientific view in Darwin’s day was that each species was immutable and the product of an independent act of divine creation. But the idea of evolution itself – or ‘descent with modification’, as Darwin called it – was not new. Many, including the naturalist’s own grandfather, Erasmus Darwin, had speculated on the notion that the various kinds of plants and animals might be derived from earlier forms and share common ancestors. Such thinking was widely condemned on theological grounds, as it appeared to displace God from his central role in creation, but without any explanation of how such modification might occur, it remained mere speculation. Indeed, the ideas of natural theology – in particular, the so-called ‘argument from design’, which inferred the existence of a creator from the wonderful complexity and order of the natural world – were generally held to be decisive in favour of the orthodox view.
Natural selection Darwin’s genius was in effect to undermine the argument from design by providing an alternative mechanism that could account for the ‘perfection of structure and coadaptation’ of living things. He went to extraordinary pains to gather evidence to support his theory and to anticipate likely objections and criticisms – it is this effort that accounts for the long years he spent ‘patiently accumulating and reflecting on all sorts of facts’. Most notably, in his own view, he made ‘a careful study of domesticated animals and cultivated plants’, where he saw a process (which he called ‘artificial selection’) closely analogous to the natural mechanism he proposed. In the end, though, the attraction of his theory was its simplicity and its capacity to reconcile otherwise-baffling facts, such as the existence of fossils and the geographical distribution of plants and animals.
‘Evolution advances, not by a priori design, but by the selection of what works best out of whatever choices offer. We are the products of editing, rather than of authorship.’
George Wald, 1957
In the Origin, Darwin succinctly summarizes natural selection as follows:
‘As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.’
‘Variation, whatever may be its cause, and however it may be limited, is the essential phenomenon of Evolution. Variation, in fact, is Evolution.’
William Bateson, 1894
This epoch-making development in biological thought thus came down to the combination of a few simple ideas: variety, heredity, competition and selection. In nature, resources such as food and mates are limited, so there will always be competition for access to them. As all individuals are different from one another, some will inevitably be better equipped than others to prevail in life’s struggles, and it is these individuals that will (on average) live longer and produce more offspring. And, to the extent that the characteristics that help an individual survive and succeed can be passed on to its offspring, those characteristics will persist and become more common in the population. So it is that, by minute and gradual changes over innumerable generations, animals and plants become better adapted to their surroundings; some species or kinds disappear, to be replaced by others that have proved more successful in the struggle for existence.
The fifth ape In the first edition of the Origin, Darwin offers no more than hints of the implications of his theory in its application to humans. He was acutely conscious of the uproar that would follow the suggestion that the difference between humans and (other) animals was one of degree only, not kind, and hence that man was not the special and favoured object of divine creation. The public furore came anyway and has blazed away ever since. Indeed, as the target of Creationists and Intelligent Design theorists, the theory of evolution, or ‘Darwinism’, is today as contentious in some quarters as it has ever been. Among the vast majority of scientists, however, the theory is unquestioned and its significance beyond doubt. As the evolutionary biologist Theodosius Dobzhansky starkly put it: ‘Nothing in biology makes sense except in the light of evolution.’
the condensed idea
Survival of the fittest