Charles Darwin’s celebrated work ‘The Origin of Species’ appeared in 1859, work that he himself described as ‘one long, continuous reasoning’. What are the consequences of the ‘Darwinian philosophy’? Has the place of mankind in nature been modified? How does Darwinian thought affect our traditional ways of thinking? Before considering the discovery itself, let us first revisit some historical facts.
The work’s construction and its immediate success
Due to its biology unifying function, Darwin’s theory is considered as an important, if not the most important paradigm of the discipline. According to the biologist Ernst Mayr, he was at the origin of a fundamental event that ‘shook the world to its foundations’. Other biologists like James Secord maintain even today the relevance of the ‘revolutionary’ vision of the history of sciences.
The first edition of The Origin of Species appeared on 24 November 1859 and sold out in only a few weeks. The second edition appeared on 28 December. The book sold 3800 copies the first year and 28,000 copies would be sold during the life of the author. Darwin already had a solid reputation as a naturalist at the moment his work was published.
Graduating from Cambridge in 1831, Darwin was employed by Henslow, his friend and professor of botanics as naturalist on the HMS Beagle’s exploratory voyage. Between 1832 and 1836, Darwin navigated the length of the South American coasts and made incursions onto land. He visited the Galapagos Islands in September and October 1835. The journey completed, Darwin published different works regularly cited by his colleagues. In 1859, Darwin’s new work was the result of years of study, patience and observations. He developed an original theory of zoology that encompasses all phenomena of the organic world. He started to write notes on the question of the ‘transmutation of species’ in 1935, and in 1944 related his ideas to a few confidents. To one friend, botanist J.D.Hooker, he writes:
I was so struck by the distribution of Galapagos organisms, ...with the character of the American fossil mammifers... that I determined to collect blindly every sort of fact, which could bear any way on what are species... At last gleams of light have come, & I am almost convinced (quite contrary to opinion I started with)... that species are not (it is like confessing a murder) immutable."Charles Robert Darwin (1809 – 1882), English naturalist whose works on the evolution of living species revolutionised biology.
He continued and finished the section on natural selection in 1957. But in 1958, he received a letter from a young naturalist, Alfred Russel Wallace containing a manuscript entitled ‘On the tendency of varieties to depart indefinitely from the original type’. Surprised, Darwin wrote to Charles Lyell:
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!"
Darwin feared that his priority over the work in which he had invested himself over 20 years would be taken away. A common reading was finally organised comprising Wallace’s manuscript, extracts from Darwin’s unpublished essay, and a letter from Darwin to the American botanist Asa Gray in 1847.
Thus ‘The Origin of Species’ released one year previously gave rise to a lively interest in 1859.
Did Darwin discover evolution?
Darwin, however, was not the first to put forward a theory on the transformation of species. The Frenchman Jean-Baptiste Lamark, and an anonymous work, released in 1844 and entitled ‘Vestiges of the natural history of creation’ had already advanced theories of the transformation of species. Darwin wrote to Reverend Baden Powell at the start of 1860:
No educated person, not even the most ignorant, could suppose that I meant to arrogate to myself the origination of the doctrine that species had not been independently created. The only novelty in my work is the attempt to show how species become modified, & to a certain extent how the theory of descent explains certain large classes of facts; & in these respects I received no assistance from my predecessors."
Thus Darwin proposed a mechanism of natural selection to take adaptation into account. But who then is the father of the theory of evolution, Darwin or Lamarck? A majority of French people recognise Lamarck’s works as precursors, yet the English unhesitatingly recognise Charles Darwin as being at the origin of the discovery. Lamarck and Darwin have a theory in common according to which living forms differ due to the accumulation of a whole series of gradual modifications. They both claim that the different groups (animal and vegetable) actually share a genealogical relationship. The two systems are however often differentiated through the overused example of ‘the giraffe that stretches its neck to reach the highest branches’. For adherents of Lamarck’s theory it is because a giraffe stretches its neck, or the use and the will, that the animal strengthens and lengthens its neck, and so becomes more and more effective at reaching high leaves. For Darwinians, a large diversity of giraffes, with both long and short necks, is born every generation. During droughts, only giraffes with long necks survive, and so, with the successive elimination of giraffes with short necks, a population of long-necked animals emerges.
In his lifetime Darwin saw his theory of evolution accepted by the scientific community and the general public
We can, then, reasonably ask ourselves what Darwin brought in addition to his colleagues in ‘The Origin of Species’.
The pillars of Darwin: variability and limitation
The first pillar of Darwin’s system is the idea that infinitesimal variations can sufficiently accumulate to produce large differences over time.
The second pillar of his system is what is referred to as the fight for existence: the fact that, as long as there are no ‘breaks’ applied, the growth rate of a species mathematically produces an abundance of individuals. As this abundance is only rarely observable, one must suppose that breaks limiting the number of individuals of any given species do exist in nature. These breaks are the existence of predators, illnesses, the limitation of resources and so on. The fight for existence is not a ‘struggle for life’, but simply the fact that, when placed somewhere, an organism faces a number of constraints that limit or hinder its multiplication.
By combining the two pillars that he isolated, Darwin deduced the idea of natural selection: a mechanism that sorts amongst variants and modifies new forms. Traditionally, the constancy of populations was explained through the wisdom of a creator who regulates the balance. Darwin was to turn these conceptions upside-down. Instead, his writings suppose that nature, such as we see it, is active and changing. Adaption for example is an active process, a process of conformation and gradual transformation of the organisation, not a fundamental principle.
The origin of species as it stands: existence, competence and responsibility
Darwin relies on the principle of vera causa to support the ideas in his work. He takes Issac Newton’s Principia, and more specifically the first of the rules included therein (entitled Regulae Philosophandi) as the starting point for his thinking. This text is essential for everything relating to ‘true’ causes
First hypothesis: we should not introduce more hypotheses than are sufficient and necessary for the explanation of observed facts
The essence of this principle is summarized as follows: A true philosophy must employ only truly existing causes in the explanation of nature; it must not search for laws by which the almighty could have produced the admirable order that reigns in this universe if he had judged it right to employ them; but only those that he really established by a free act of his will... cf Mathematical Principles of Natural Philosophy.
So Darwin had difficulty proving that the natural selection that he had described is a cause – that is to say that it exists and that it is competent. In 1863 he wrote to the botanist Georges Bentham:
In fact, the belief in natural selection must at present be grounded entirely on general considerations. (1) on its being a vera causa, from the struggle for existence; & the certain geological fact that species do somehow change (2) from the analogy of change under domestication by man’s selection. (3) & chiefly from this view connection under an intelligible point of view a host of facts."
Darwin also refers to the epistemological principle of ‘consilience’ developed by William Whewell to support his ideas. The term designates the type of display that appears as numerous independent sources converge to discern a particular historic phenomenon. The ‘consilience’ research strategy consists of coordinating apparently disparate results and gathering facts from different sources within the same, coherent group. I the last chapters of The Origin of Species, Darwin shows that natural selection is at the centre of a ‘consilience’.
Thus, in The Origin of Species Darwin poses a three-pronged question:
- The existence of natural selection. This is established in chapters I and II of the work. Darwin shows that there are conditions of variation in domestic and wild species as well as a struggle for survival that occurs following the differential reproduction of individuals.
- The competence of natural selection. This selection exists today and functions in favour of the formation of species and their adaptive diversification over the long term, in genres, in families and so forth. This concept is established in chapter IV of the work. Natural selection is much more powerful (both in scale and over time) than artificial selection.
- The responsibility of natural selection in the production of new species. Natural selection has probably been the primary agent in the production of species that exist today. From chapter IV in the work, Darwin attempts to regroup different geological, geographical, morphological and embryological facts in relation to present and extinct species.
The origin of species made evolution (from a common ancestry) the dominant scientific explanation of the diversification of natural species.
To conclude, in The Origin of Species Darwin advances a theory of descent with modification that functions in a two-step process. First of all, a large number of variations are produced in all directions. Next, a process of natural selection guides the evolution, not by imposing a fixed direction, but in reaction to circumstances. Thus Darwin equipped the theory of evolution with a general theoretic model and a reliable mechanism that proved itself to be extremely fruitful. What is more, the Darwinian mechanism allowed the unification of many different fields of biology. Embryology, palaeontology, geographical species distribution, and comparative anatomy all entered into a common paradigm.
If, from a Darwinian point of view it is false to say that ‘mankind descended from the monkey’, one must however accept that mankind and the monkey have a common ancestor. Darwinism is a constant reminder of the resemblance and the affinity between humans and animals.
© Tony Baggett; Duris Guillaume; kamphi – Fotolia.com
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1) The Origin of Species, originally entitled On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, Charles Darwin, translation by Edmond Barbier, verified by Daniel Becquemont, Flamarion.
2) Thierry Hoquet, Darwin contre Darwin, Comment lire l’Origine des espèces ? Paris, Le Seuil, collection « L’ordre philosophique », 2009