“There is probably no more original, more complex, and bolder concept in the history of ideas than Darwin’s mechanistic explanation of adaptation.”
– Ernst Mayr in The Growth of Biological Thought (1982), p. 481.
Charles Robert Darwin (1809-1882), one of the many grandchildren of Erasmus Darwin (an equally remarkable person), provided the world with the knowledge of a natural mechanism which explains the gradual appearance of organismal traits, backed up by tons of evidence from fossils to domesticated animals, and an appreciation of the immense time span during which this mechanism can act. The last paragraph of Charles Darwin’s Origin of Species has inspired thousands – me included – to embark on a journey to study life in all its glorious diversity.
Charles Darwin’s theory of natural selection, as explained in his book On the Origin of Species (the ‘On’ being dropped in the 6th edition) layed the foundation for modern biology and catalysed a philosophical shift in society (look no further than Russia, where the popularisation of evolution by the plant physiologist Kliment A. Tymiriazev played a key role in its secularisation). As Darwin put it in his Autobiography, “We can no longer argue that, for instance, the beautiful hinge of a bivalve shell must have been made by an intelligent being, like the hinge of a door by man.” The age-old (dating back to Socrates (469-399 BC) and popularised by William Paley in his 1802 book Natural Theology) argument from design was conclusively demolished.
Instead, we have what Herbert Spencer called the “survival of the fittest”. Spencer was a liberal politician and sociologist and coined the term in his Principles of Biology (1864), although in relation to free market economics; Darwin incorporated it in the fifth edition of the Origin onwards. Nonbiological connotations aside, it encapsulates the notion of natural selection as a filter through which only the organisms best adapted to their environment can survive. Or, as Darwin puts it, “the preservation of favorable variations and the rejection of injurious variation”. These adaptations, over a single generation, are slight differences between individuals – a larger eye, longer legs, a coloured spot on the wing – that can cause those individuals to survive to reproductive age (see the picture above (Gregory, 2009)). Darwin’s true genius was to recognise that this process has been continually happening since life first originated. As those suriviving individuals produce more offspring, their traits get passed on and become more common in the population. Over the eons of geological time, this has led to the diversity of life on Earth. The argument from design was made meaningless: over time, as the successful variants reproduce more, they will appear to be designed – yet this apparent design is the reuslt of natural causes, namely Darwin’s natural selection.
This insight has given Darwin the rightful status of the greatest naturalist to have ever lived (and also leads to a bit of hero-worship, an activity that should be strongly discouraged). His impact stands right up there with Nicolaus Copernicus’s, Galileo Galilei’s and Isaac Newton’s. Copernicus’s 1543 De Revolutionibus Orbium Celestium (On the Revolutions of the Celestial Spheres) proved that natural laws govern the universe. Charles Darwin’s Origin proved that natural laws govern the biosphere. Both led to a crisis of faith – the Earth was no longer the special centre of creation and organisms were not designed and created. It was the natural extension to biology of the revolutions that had already taken place in physics, astronomy, chemistry and geology.
In the note of fairness, there are some dissenters (for lack of a better word) who argue that he “lied, cheated and plagiarised in order to be recognised as the man who discovered the theory of evolution” (Davies, 2008, p. 162). A more down-to-Earth, but still somewhat conspiratorial paper to consult is Wainwright (2010). Their thesis is that Darwin stole all the ideas about evolution from literature available at the time, without citing any references. A common misunderstanding, also among the general public, is that Darwin ripped off Alfred Russel Wallace. Both these views are strawmen of Darwin’s achievement. Wallace had come to the same model, but had not accumulated nearly the amount of evidence that Darwin had accumulated.
Were ideas about “common descent” around at the time? Of course. Same goes for notions of natural selection. We refer to them collectively as pre-Darwinian transmutationists (transmutation is what descent with modification was known as). Famous figures included Erasmus Darwin (in his posthumously published poem The Temple of Nature), French zoologists Jean-Baptiste Lamarck (1744-1829) and Étienne Geoffroy Saint-Hilaire, publisher Robert Chambers (1802-1871), physician (and Darwin’s mentor) Robert Edmond Grant (1793-1874), geologist Robert Jameson, Pierre Maupertuis or Georges-Louis Leclerc (a.k.a. Comte de Buffon). Of those, Jean-Baptiste Lamarck was the most prominent and his ideas caused great debates in the 1820s and 1830s. Opponents of transmutation (e.g. William Whewell and Charles Lyell) all focused on him; proponents crowded around him. Noticeably not on the list of pre-Darwinian transmutationists is Georges Cuvier and his student Alcide d’Orbigny – a much better naturalist than Darwin (d’Orbigny had a knack for detail, Darwin for the larger picture).
Darwin would surely have come across their works and been influenced by them. He denied being influenced by Lamarck directly, but an indirect influence is almost certain (through his teachers and the scientific Zeitgeist of the time). As a summary, Lamarck was a significant zoologist and botanist in the 19th century and certainly the most important pre-Darwinian evolutionary biologist. Lamarck posited that species were created many times in the form of their Platonic ideal, and they then got modified according to how much they used or disused their organs; at the origin of this process is a change in behaviour and mechanistically, Lamarck invoked a “nervous fluid” within each organ and structure that stretched it and modified it, changes to be passed on to the next generation. That we have such radically different animal morphologies is explained by saying that the more complex animals originated earlier and so are more modified. Also of note, Lamarck was the first to popularise such terms as “biology”, “invertebrate”, “annelid”, “arachnid”, “crustacean” and “tunicate”.
One scientist in particular stands out among the rest: Giambattista Brocchi, an Italian palaeontologist who wrote much on the similarities between modern molluscan fauna and fossil/subfossil molluscs, and his ideas on species were more or less identical to Darwin’s (and Brocchi was writing first). But nobody until Darwin delivered the empirical proof of all of this and synthesised all of these disparate thoughts into a single, coherent model applicable to life in its entirety. This is why we credit and praise Darwin. As George John Romanes put it in Darwin’s obituary in Nature, Darwin is remarkable for his “many years of labour whereby he tested this idea in all conceivable ways – amassing facts from every department of science”.
As an aside, some have argued that had Darwin and Wallace not existed, natural selection would have been discovered at the time anyway. They point to the precedent of scientific revolutions happening when the societal climate was right. In Victorian England, talk of competition for survival was rife. Charles Dickens in 1846 had published a book called The Battle of Life: A Love Story. Thomas Malthus (1766-1834) published An Essay on the Principle of Population, wherein he took a pessimistic view on population control where famine and other struggles for resources serve to keep the booming human population in check (see Appendix 1) – Darwin himself admits this essay influenced his thinking. Thomas Henry Huxley (1825-1895) in England, Ernst Haeckel (1834-1919) in Germany or Asa Gray (1810-1888) in the USA are all prime candidates who could plausibly have discovered it.
Thomas Henry Huxley, a.k.a. Darwin’s Bulldog, was a zoologist, comparative anatomist, philosopher and education planner. He was also a flaming agnostic (he popularised the term) and the founder of Nature (1869). One of his discoveries is that birds are dinosaurs, and he created the names “Hydrozoa” and “Sauropsida” (among others). The Huxley line is in general quite famous even now thanks to his three grandchildren: writer Aldous Huxley (Brave New World), biologist and UNESCO general secretary Julian Huxley (discoverer of allometry and one of the architects of the Modern Synthesis) and 1963 Nobel Prize in Physiology or Medicine laureate and biophysicist Andrew Huxley (of Hodgkin-Huxley equations fame).
Ernst Haeckel, the German zoologist, anatomist, freethinker, artist, doctor, philosopher and science populariser was the spreader of Darwin’s ideas in Germany, a role no doubt helped by his professorship in zoology at the university of Jena. He developed the concept of phylogeny, using tree diagrams to illustrate the relationships between organisms on Earth. He popularised and defined the term “ecology”, described thousands of species and drew them in spectacular paintings. His Generelle Morphologie was a highly-influential textbook. Nowadays also known for his now-disproven theory that “ontogeny recapitulates phylogeny” (also known as recapitulation theory or biogenetic law).
Charles Darwin himself was seemingly the best candidate though. He was brilliant, humble and a perfectionist. He had intuition, creativity and a curiosity that extended to all parts of the natural world, from extinct animals, to orchids, to earthworms, to barnacles, to finches, to pigeons, to climbing plants, to volcanic islands, to self-fertilisation. Everything in the natural world excited him.
But it cannot be denied that some hyperboly always accompanies such iconic scientists as Darwin. The image of Newton as an eccentric man of genius is a creation of the British scientists of the 19th century. Michael Faraday received a similar treatment, as did Darwin – although with Darwin, it began as he was still living, in the last 20 years of his life (who could mistake that beard designed specifically to make him look like a prophet?). By his death, he was “for some a secular saint, for others the epitome of wisdom, respectability and honesty, a man who cautiously and assiduously accumulated a mountain of evidence in order to overturn humanity’s view of itself” (Browne, 2005, p. 257). He was a mystery to the public – he had toppled religion’s hold on society, yet nobody knew what his beliefs were, other than probably a deist. And this knowledge was considered crucial to understanding how his theory of evolution was meant to be understood. The image of Darwin was free to be manipulated, with the view of him we have now having been set since the rediscovery of Mendel’s work in 1900 (by Hugo de Vries (1849-1935), Carl Errich Correns (1864-1933) and Erich von Tschermak-Seysenegg (1871-1962)) and the 50th anniversary celebrations of 1909.
A total of 10 biographical books were published in the 18 years after his death. All sought to portray Darwin as an upstanding man of virtue and science, and not much was actually written about his theory. In fact, most simply stated that while theology was now garbage, teleology has made a comeback, and left it at that (implying the true nature of natural selection would have been too controversial). Of course, there were exceptions. Bacon emphasised natural selection, while Bettany fell back to the same old canard that many evolutionists are Christians, therefore they’re compatible; in fact, he goes further and states that natural selection supports natural theology. The first set of biographies, listed below, came out during the first five years.
Louis Compton Miall (1842-1921, entomologist). “Life and Work of Charles Darwin”, 1883.
George Washington Bacon (1830-1922, map publisher). “The Life of Charles Darwin with British Opinion on Evolution”, 1883.
Grant Allen (1849-1899, science populariser). “Charles Darwin”, 1885.
George Thomas Bettany (1850-1891, anthropologist, historian). “Life of Charles Darwin”, 1887.
Then came the monumental Life and Letters of Charles Darwin (1887), by Charles Darwin’s son Francis Darwin (1848-1925) and included an autobiography. It showed how Darwin struggled personally to get to grips with his theory of natural selection, how he worked tirelessly to “force the truth to reveal itself” (Darwin, 1887, p. 149).
The next set of biographies attempted to decouple Charles Darwin (the person) from his theory – to let them both stand on their own merit. The first two are children’s books. Here, we notice that natural selection and its implication had become settled in society: Poulton feels no reservations about blasting those who still support natural theology (including Grant Allen and T. H. Huxley).
Walter Mawer (natural history magazine editor). “Truth for Its Own Sake: The Story of Charles Darwin Written for Young People”, 1889.
Charles Frederick Holder (1851-1915, naturalist, museum curator). “Charles Darwin: His Life and Work”, 1891.
Earnest Albert Parkyn. “Darwin: His Work and Influence”, 1894.
James Hutchison Stirling (1820-1909, philosopher). “Darwinianism: Workmen and Work”, 1894.
Edward Bagnall Poulton (1856-1943, zoologist). “Charles Darwin and the Theory of Natural Selection”, 1896.
Three themes dominate all these biographies: Darwin as a scientist, Darwin’s character and Darwin’s beliefs, and their conclusions directly shaped how we view Darwin today. Of course, they were also influenced by the climate of society at the time.
In the 18th and early 19th century, science was viewed as advancing by momentary flashes of genius – an apple falling from a tree on to Newton’s head due to gravity, William Herschel immediately identifying a new planet without any calculations. This was the Romantic ideal of a scientist. In the Victorian era, this was changing to cultivate a picture of the working scientist, conducting slow, thorough experiments, sacrificing his opinions in order to adopt the new evidence as it comes – the true objective, rational scientist. The natural historian – one who tried to order nature from a natural theology perspective – was being replaced by the biologist – one who studies organisms for their own sake.
Emphasis was placed on Darwin’s observational talents – this was especially common in books for children. He was portrayed as the ultimate field naturalist, looking at the world with wonder, noting down the intricacies and the details, the raw material for his theory, and how it was that because of Darwin’s observational prowess, “now all the world looks at things differently” (Anon, 1880, p. 13) – Darwin and his theory taught us how to properly look at life. Of course, as Holder’s biography says, “nothing escaped his watchful eye,” (p. v) and some remarked on Darwin’s geology and anthropology. The final effect is a picture of Darwin as being as one with nature as possible, a view encapsulated in the picture above, taken from Holder’s biography.
Of course, this view clashed with Francis Darwin and T. H. Huxley’s portrait of the experimentalist, which emphasised long hours spent in isolation, deep in his thoughts, considering how to further probe nature to make her reveal her secrets. They were reconciled in Poulton’s biography, where Darwin was a discoverer. In this account, the observations made by Darwin during the Beagle voyage were the grape juice to natural selection’s wine [Author’s Note: excuse my horrible metaphor]. “Powers of observation, however acute, could never make a scientific discoverer; for discovery requires the creative effort of the imagination,” writes Poulton. This imagination expressed itself in Darwin the experimentalist.
On the nonscientific aspects of his life, he was unanimously agreed to have been a moral, upstanding saint – this is the way to interpret the picture above: he’s the repectable, gentlemanly unbeliever. In fact, much of what was written about this could well be classified as hagiography (e.g. Mawer’s biography states that Darwin “was destined to become the most illustrious of the good and noble since Jesus and Socrates”) – no doubt to counteract the notion of the time that only Christians could be moral. It was politically needed: most of his critics, much like the creationists of today, were unscientific dolts who objected to natural selection due to misplaced ethical and religious reservations. Their criticisms were as laughable as they are today, and include such gems as evolution is immoral aestheticism or that the Descent of Man is pornographic. The only exception to the biographies that portrayed Darwin’s character as good was by the deeply religious philosopher James Hutchison Stirling, in which he calls Darwin an attention-seeking “arch little rogue”. Stirling was also a huge fan of German idealism and viewed Darwin as some sort of demonic High Priest of materialism, stating that it “has had an enormous advance since Darwin: from him on, my brethren, the doctors have had it all their own way” (as if that’s a bad thing).
Hysterics aside, what did Darwin believe? Edward Aveling, in his 1883 book Religious Views of Charles Darwin tried to pass him off as an atheist. Darwin himself states in an 1879 letter that he was a theist while writing the Origin, but then became an agnostic. On the concept of an intelligent God, he displayed some classic skepticism: “can the mind of man, which has, as I fully believe, been developed from a mind as low as that possessed by the lowest animals be trusted when it draws such grand conclusions?” Of course, his religious views were something of a taboo subject, and Francis Darwin’s Letters were carefully selected to maximise the public’s perception of Darwin’s character.
Biographies begged to differ, though. Mawer ridiculed any notions of a religious Darwin with such classic lines as “His devotion to Truth as Truth, when assailed most bitterly and violently by orthodox people, and his meekness under these assaults, never returning one unkind word upon his adversaries, together with his universal benevolence … reveal a religious mind more than does a professed adherence to all the creeds,” or commenting on the “bitter theological hatred which has so often disfigured the search for truth”. Holder claimed Darwin “was a firm believer in a First Cause”, i.e. a liberal Christian. So the question is ultimately unanswered.
By the way, a note on the last paragraph of the Origin, with the bit about the Creator. This was not present in the first edition. All subsequent edition of the Origin, while including precious updates (e.g. Archaeopteryx, the first feather of which was found in the years of the Origin’s first edition, with the first skeleton coming next year and another one several years later, or Batesian mimicry included since the 4th edition), had to have some emendations added for political correctness – the Creator line being one of them. It was not representative of Darwin’s thought, as can be seen in this 1863 letter to Joseph D. Hooker: “But I have long regretted that I truckled to public opinion, and used the Pentateuchal term of creation, by which I really meant “appeared” by some wholly unknown process.”
Similarly unanswered were the interpretations of the ‘deeper meaning’ of natural selection. Miall and Parkyn combined natural selection with teleology and a notion of progress, Bettany used it to support natural theology, while Allen applied it to the entire world – cosmos and all. Poulton was the sensible one, seeing it for what it is: a mechanism that explains the diversity of life. A purported link between philosophy (especially moral philosophy!) and evolution exists only in those vacant cavities that pass for brains of creationists and other “skeptics” (for the best example of this, see Benjamin Wiker’s 2002 book Moral Darwinism, where he traces the decline of moral society with the rise of materialism. Do not keep desks or palms near your face or head while reading this book).
Darwin’s conviction in the truth of natural selection was exemplary, and at times prophetic. On human evolution, he matter-of-factly stated that “Much light will be thrown on the origin of man and his history” due to his theory. Furthermore, he predicted that Africa would be the cradle of humankind – despite the fact that no human fossils were known at the time. Some would brand him as provocative because of this. No. He simply pursued the truth for the sake of knowing it – and he was not afraid of admitting his limitations, for example when he calls the origin of the flowering plants “an abominable mystery” in an 1879 letter to J. D. Hooker. This is the quintessential scientific attitude.
Manipulations of history aside, one thing is clear: Darwin was a hard worker and extremely productive. After publishing his accounts of the HMS Beagle voyage, he could very easily have retired in his Downe mansion; he was rich and set for life, after all. But he didn’t, and this tells us all we need to know about his character: that he was not some attention-seeker, as Stirling implied, but a curious scientist searching for the truth at any cost, both mental and physical (imagine undertaking a Beagle voyage back then, away from civilization for months, with no hopes of rescue should any accident happen and at risk of getting infected by all sorts of unencountered diseases with no cure).
He was a loner and did not participate much in public discourse – that was left to T. H. Huxley, most memorably when he gave Bishop Samuel ‘Soapy Sam’ Wilberforce a thorough spanking at an Oxford Museum meeting. In Darwin’s defence, while he could have suspected that some would be offended by the contents of his writings, he couldn’t have predicted that such a social firestorm would erupt, especially since the facts were on his side. He was also quite sick after his return to England, possibly due to Chagas disease (a condition made worse by his hypochondriac tendencies).
Ernst Mayr summarised this social opposition thus: “No other work advertised to the world the emancipation of science from philosophy as blatantly as Darwin’s Origin. For this he has not been forgiven to this day”. Whereas before, humans were special, now we are nothing more than apes. We are a part of nature, not above it. Another point of contention was geological time. James Usher (1581-1656), Anglican Archbishop of Armagh and Primate of All Ireland in 1625-1656, calculated that the Earth was created by God on the night of 22nd October 4004 BC. This magic date was held as dogmatic truth until James Hutton (1726-1797) and, much more thoroughly, Charles Lyell (1799-1875) demonstrated how slowly geological processes take place. Lyell, by the way, was one of the founders of modern geology, with his greatest contribution being the principle of actualism: that processes taking place now have been active during Earth’s entire history, overturning the then-predominant catastrophism theory. He revolutionised the field of stratigraphy; he also was the first to conclusively show that humankind is much, much older than was thought at the time. Lyell greatly influenced Darwin (Darwin was also a geologist and read Lyell’s books) and his Principles of Geology lay behind Darwin’s insistence on the enormous time span of organic evolution (Lyell himself accepted this, eventually, but never for humans). If the age of the Earth was not a problem, the age of the Sun was. Before Henri Becquerel (1852-1908) discovered radioactivity in 1896, William Thomson (1824-1907) had calculated that the sun was 20-40 million years old, so this was another stumbling block (albeit a more reasonable one).
He was a family man, his wife Emma Darwin (née Wedgewood) (1806-1896) standing behind him the whole time, even though his theories directly contradicted her strong Christian beliefs.
One question of interest is when exactly did Darwin think up that species were not fixed. There are two hypotheses: the early conversion and the late conversion hypotheses. In the former, the vertebrate fossils he had found in South America plays a key role, as can be seen from the very first sentence of the Origin: “When on board HMS Beagle, as naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to throw some light on the origin of species.” Basically, it was during the voyage that Darwin had begun to question the concept of the immutability of species. However, in an 1877 letter to German naturalist Otto Zacharias, he wrote: “When I was on board the Beagle, I believed in the permanence of species but, as far as I can remember, vague doubts occasionally flitted across my mind. On my return home in the autumn of 1836, I immediately began to prepare my journal for publication, and then saw how many facts indicated the common descent of species so that in July 1837, I opened a note-book to record any facts which might bear on the question. But I did not become convinced that species were mutable until, I think, two or three years had elapsed.” In other words, he hadn’t thought of it until after he was back in England.
He contradicts himself, so we can’t really take his word for it. George Gaylord Simpson wrote that “Darwin’s collections of fossil mammals could not and did not lead directly to evolutionary conclusions. [N]one of [his] fossils could reasonably be considered as ancestral, in an evolutionary sense, to any living species.” Transmutational thoughts can be traced in his Diary, when he commented on the fer-de-lance snake in Bahia: “I also caught a large snake, which at the time I knew to be venomous; but now I find it equals in its poisonous qualities the Rattle snake. In its structure it is very curious, and marks the passage between the common venomous and the rattlesnakes. Its tail is terminated by a hard oval point, & which, I observe, it vibrates as those possessed with a more perfect organ are known to do so.” In his zoological notes, he goes further and writes “how beautifully does this snake both in structure & habits connect Crotalus & Vipera”. That’s evolutionary thinking right there. Lyell’s Principles of Geology Volume 2 was a point by point refutation of Lamarckianism, so Darwin was already aware of the concept. His observations of both geographic (especially with the birds) and temporal (fossils) replacement of species had already triggered transmutational thoughts in his mind. Whether he was personally convionced of it, we can’t know. I personally find it very likely: he landed on the Galápagos fully expecting to find a varied form of South American flora and fauna, as he had already experienced in the Falklands. To me, that says that he was already thinking in terms of evolution.
Darwin’s complete conversion to transmutation definitely took place on opening his first notebook on transmutation in July 1837.
Random note: his nickname in school was “Gas”, because he had a great interest in chemistry.
He wasn’t a book worshipper. For him, books were tools and he didn’t go to great lengths to take care of them. Large books were cut in half so he could easier hold them; uninteresting pages were torn out and discarded to save space. In later years, the margins would be filled with Darwin’s scribbled notes. After finishing with a book, he wrote a summary of it.
Now that we’re done with Darwin as a person, some history on the Origin‘s origin [Author’s Note: I just had to write this line, no matter how cringe-worthy].
In 1844, Robert Chambers published Vestiges of the Natural History of Creation. Its reception by the scientific establishment was hostile; all reviews were devastating. This made Darwin nervous, as by then he had completed two sketches of his own about the question of the origin of species. He saw it as a sign of what would happen if he published his ideas prematurely: Chambers’ book was full of speculation and errors. Hence Darwin set to work amassing evidence in his favour. He started establishing himself firmly as a respectable biologist with many publications (such as his barnacle classification, completed in 1854), culminating in Royal Society Medal to cement his reputation among the scientific community.
In 1858, Darwin received a letter from the Far East, sent by Alfred Russel Wallace (1823-1913). It was a manuscript containing a theory of natural selection similar to his, wherein Wallace concluded that “the life of wild animals is a struggle for existence”. Like Darwin, Wallace was also inspired by Malthus’s essay. Encouraged by this, Darwin asked Charles Lyell (1797-1875) and Joseph Dalton Hooker (1817-1911) to read both manuscripts at a meeting of the Linnean Society. The reception was cold. But then Darwin published his Origin of Species. This single-handedly shook the entire world, explaining the diversity of nature in a mechanistic, not supernatural way. In 1889, this was followed up by Alfred Russel Wallace’s book Darwinism, which explained the theory again, as well as took down the common arguments against it.
Contrary to popular perception, The Origin was not Darwin’s planned magnum opus. To him, it was merely an abstract he had rushed to prepare after Wallace’s surprising letter – hence why it contains no references. His final work, Natural Selection, is in bits and pieces in the form of several manuscripts published posthumously by his son in 1909. He had been working on it since his return to England. In 1855 he wrote to William Darwin Fox saying, “I am hard at work at my notes [from the Beagle voyage] collecting and comparing them, in order in some two or three years to write a book with all the facts and arguments, which I can collect, for and versus the immutability of species”. Progress was slow, as he wrote to Lyell in 1856: “I have found it quite impossible to publish any preliminary essay or sketch; but I am doing my work as completely as my present materials allow without waiting to perfect them”.
Then came Wallace’s letter and the reading of the manuscripts for the Linnean Society. Darwin then told Wallace in January 1859 that “I look at my own career as nearly run out. If I can publish my Abstract [On the Origin of Species] and perhaps my greater work on same subject [Natural Selection], I shall look at my course as done”. In November 1859, The Origin was published. His “big book”, as he liked to call it, never came.
In 1975, after no doubt painstaking work (Darwin had shitty handwriting, see letter above and try to find where he writes “abominable mystery”), Stauffer had transcribed over 1000 pages of Darwin’s manuscripts and spliced them together in the book Charles Darwin’s Natural Selection: Being the Second Part of His Big Species Book Written from 1856 to 1858. As Mayr wrote in his 1992 book Natural Selection, “Darwin presented his reasoning and his evidence in far greater detail than in the Origin of Species. This permits a new and indeed more definitive analysis”. And it’s true – Natural Selection, or what we have of it, is phenomenal and is a true demonstration of Darwin’s scientific abilities.
Back to Wallace, he was not a poor man, although he started off as one. By the time that this whole story went down, he was settled, built a large complex of houses and wrote many, many books – he was an excellent science populariser. But he is now also known as the father of zoogeography (not biogeography – that was von Humboldt), discovered the Wallace Line (a distinct line between Asia and Australia, with the faunas on both sides of it being very different), pioneered the concept of ß-diversity (not known as that back then, of course) and he also discovered the Wallace effect, where natural selection produces barriers between two varieties in a population, leading to speciation. He also wrote extensively on mimicry and described plenty of new species. He was married to Anne Mitten (1846-1914) and was a very influential social activist.
Darwin also published other books, although they were more academic in nature, all containing the results of his experiments and/or further thoughts on evolution. His systematic treatise on barnacles remains to this day one of the best examples of how to do systematic biology. He also researched orchids and insects and their co-adaptations, climbing and insectivorous plants, plant reproductive diversity, domesticated animals, emotions (with experiments conducted on his dog Polly) and earthworms. On the theoretical front, sexual selection and human evolution were the topic of his Descent of Man.
Both Wallace and Darwin were avid entomologists: Darwin was Vice President of the Royal Entomological Society in 1838 and Wallace its President in 1870-1871 (back then, it was known only as the Entomological Society, the ‘Royal’ tacked on at the 100 year anniversary in 1933). Darwin had a love of beetles (“Whenever I hear of the capture of rare beetles, I feel like an old warhorse at the sound of a trumpet”), Wallace of lepidopterans (moths and butterflies).
Darwin’s coleopterology was nothing strange: beetle-collecting was a favourite pastime among students in Victorian England, most probably a response to the recent expansion of urban areas. His cousin William Darwin Fox was also a coleopterologist. During the Beagle voyage, he noted the distributions of beetles. He collected beetles living in the open sea, unaffected by salt water (the aquatic ones were drifted there by a stream, the terrestrial ones blown by the wind – or so he assumed). In the Origin, he used the modifications of aquatic beetle legs as evidence for natural selection. Despite his passion for beetles and entomology in general (he devoted a whole chapter in the Descent of Man to butterflies), he never did pursue beetle or insect systematics, instead choosing (somewhat surprisingly) the barnacles (crustaceans).
With the cast list done, a short note on the Beagle voyage (I won’t be narrating the whole thing!). The HMS Beagle, carrying 75 people on board, was captained by Robert FitzRoy, a man only 4 years older than Darwin (Darwin was 22 when they left England). The purpose of the voyage had nothing to do with biology: the South American coast had to be charted, and some longitudes had to be measured with new, more accurate instruments. FitzRoy had asked John Stevens Henlow, Darwin’s botany professor, to recommend a companion for the trip – he would have been awfully lonely, as the captain was not supposed to converse with his sailors. Darwin was not the official naturalist – he only got that position when Robert McCormick ditched the ship in Rio de Janeiro.
With him, Darwin took a small 6×4 inch microscope, a compass, a taxidermy book, a geological hammer, a Bible, Milton’s Paradise Lost, Lyell’s first volume of the Principles of Geology (with the second and third volumes arriving later), a magnifying glass, plenty of alcohol for preserving specimens, and German naturalist Alexander von Humboldt’s Personal Narrative. Darwin was seasick throughout the whole voyage, sometimes spending days eating only raisins (back then thought to be a cure for seasickness), which is why he spent as much time on land as possible, and why he never left England again after returning.
The voyage took 4 years, 9 months and 2 days. The first stop was St. Jago, Cape Verde Islands, where he found fossilised shells that seemed to belong to the same species as those that were on the beach. 63 days after setting off, they set anchor in Bahia (El Salvador), where Darwin ate his first banana “but did not like it, being maukish and sweet with little flavor”. He also encountered slavery and ranted uncompromisingly against it, as he also did against the genocide of indigenous people by colonialists. At Punta Alta and Mount Hermoso came significant finds: giant extinct mammal fossils (e.g. giant sloth). This caused some stirring thoughts in his mind about why these animals were no longer alive.
In Chiloé off the coast of Chile, Darwin saw a volcanic eruption (Mt. Osorno). From 15th September to 20th October 1835, he was on the Galápagos Islands, where his keen observant eye and active mind were delighted – the five weeks he spent there were the most influential on his thinking. He saw giant tortoises: “In my walk I met two very large Tortoises (circumference of shell about 7 ft). One was eating a Cactus & then quietly walked away. The other gave a deep & loud hiss & then drew back his head. They were so heavy, I could scarcely lift them off the ground.” I do not know why he wanted to lift the tortoise. He also tried to ride it. We can identify three observations that got Darwin really thinking about transmutation. “My attention was first thoroughly aroused, by comparing together … the mocking-thrushes, when, to my astonishment, I discovered that all those from Charles Island belonged to one species (Mimus trifasciatus); all from Albemarle Island to M. parvulus; and all from James and Chatham Islands … belonged to M. melanotis,” he says in the Voyage of the Beagle. Basically, he noticed that closely-related populations vary in their appearance on every island. The second observation is that “It is probable that the islands of the Cape de Verd group resemble, in all their physical conditions, far more closely the Galapagos Islands, than these latter physically resemble the coast of America, yet the aboriginal inhabitants of the two groups are totally unlike; those of the Cape de Verd Islands bearing the impress of Africa, as the inhabitants of the Galapagos Archipelago are stamped with that of America.” In other words, the populations’ affinities are determined more by biogeography, not by physical conditions. The third realisation came after his return to England, when the ornithologist John Gould confirmed to Darwin that the birds he had observed on the Galápagos were all members of the same family: the Darwin finches. “Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species has been taken and modified for different ends.” And so it was that Darwin officially became set on his theory of descent with modification.
Basically, it was on islands where Darwin’s thoughts were first really set in motion. He made other observations which we now realise are also intimately tied to evolution on islands: that trees have large seeds and so are poor long-distance dispersers was noted by Darwin – we now know that this is why young islands have many tall plants with tree-like morphologies, as they grow taller to compete for light in the absence of the trees. He noted the evolution of flightlessness in many island birds (“A gun is here almost superfluous; for with the muzzle I pushed a hawk off the branch of a tree”) and insects, explaining them in a nifty metaphor: “As with shipwrecked mariners near a coast, it would have been better for the good swimmers if they had been able to swim still further, whereas it would have been better for the bad swimmers if they had not been able to swim at all and had stuck to the wreck.” Similarly, he noted the loss of dispersal abilites in island land animals and plants. On inhabited islands, he noted the evolution of tameness in many vertebrates (I doubt any other tortoise would have allowed him to ride it). While we can now explain the reasons for all of these observations, they follow directly on from Darwin’s observations (take not of that, those biologists who think field naturalists are now a thing of the past).
Moving on to Tahiti, he lamented the difference between the unspoiled “Paradise” that Joseph Banks had sailed to in 1769 and the colonialised mess that the Christian missionaries had turned it to. In general, he made many comments on the loss of biodiversity, e.g. “It is impossible to reflect on the changed state of the American continent without the deepest astonishment. Formerly it must have swarmed with great monsters: now we find mere pigmies, compared with the antecedent, allied races.” Wallace had similar concerns: “We live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared.” In all these islands, Darwin commented on the unusual character of the floras, noting that they were different on every island. In the Falklands, he described the now-extinct Falkland wolf and its strange appearance. After spending time in this area of the world, they set off to Tasmania and New Zealand, then to Mauritius and Cape Town, returning quickly to South America before going through the Azores and back to England.
Some more randomness: Darwin was one of the first to study aerobiology, collecting air samples and finding “17 different organic forms” (interestingly, these samples were reexamined recently and the organisms were still alive (Gorbushina et al., 2007)). Louis Pasteur was the first guy to systematically study aerobiology though.
From a palaeontological point of view, while he discovered some gigantic fossil oysters, much has been made of his vertebrate fossil finds. These included ten ‘megafaunal’ animals and two rodents; I compiled most of them in the picture up there. They were what caused him to start thinking about how modern species could be replacing the extinct forms – he knew that they were related to modern forms, but that they had clear differences. Why would they go extinct? (Hint: Natural selection.)
If you really want to know all the details, then read Darwin’s Voyage of the Beagle. In fact, I recommend reading that before moving on to the Origin, since it allows you to really trace how his mind was working and how his ideas were falling into place. It also serves as an excellent travel guide: as I said already, Darwin was an excellent observer, and you can tell by the entries in his journal, where the amount of detail is enough that you can picture yourself walking alongside him making notes.
To finish off, let’s take a look at some aspects of Darwin’s work. Not a review, just random notings and musings.
First, speciation, the “single most important event in evolution” (Mayr, 1963, p. 11). Darwin’s theory of natural selection explains how populations change morphologically and ecologically as the environment changes. Speciation is simply the end point of this: from all the individual variations come adapted varieties, and this, coupled with extinctions, leads to new species. In other words, new species arise because of changes in the environment – ecological speciation. He didn’t acknowledge the role of geographical barriers in speciation, and the general consencus nowadays is that his view of speciation was at best very muddled. As some biologist [I could not find who or where this comes from] said once, “Sometimes I think that Darwin, at least on speciation, is like the Bible: one can buttress any view by choosing the right quotations”.
He did not have a definition of species, telling Joseph D. Hooker in 1856 that the term is “undefinable”, due to his theory now dismantling the idea of a species being a fundamental, unchanging building block of nature. Despite its title, On the Origin of Species was not much focused on explaining the origin of species, since species was now a meaningless, arbitrary term. This discrepancy between book title and book content was noted from very early on, even by supporters including T. H. Huxley and George John Romanes, and later much more thoroughly by Ernst Mayr; it is now common to see the anecdote in any evolution textbook or book on speciation.
Speaking of terms, Darwin was initially not fond of the term “evolution”, preferring “descent with modification”. The reason is that back then, evolution had a different meaning and was used by embryologists such as Ernst Haeckel to describe ontogeny (development from embryo to adult). This carried on from the earlier tradition when evolution was used in its literal meaning “to unroll”: earlier embryologists thought that embryos came prepackaged with all the adult organs and tissues (homunculi) and simply ‘unrolled’ into the adult. Haeckel translated descent with modification as transmutation or transformation. In Germany, evolution only got its modern meaning in the 1920s. As of the 6th edition of the Origin though, Darwin had already become comfortable with the word evolution, after being convinced by Herbert Spencer’s use of it. Herbert Spencer also co-opted the term fitness to use in an evolutionary context. Darwin was very grateful to Spencer.
On human evolution, unlike what most people who’ve never read his works say, Darwin never claimed that humans and chimps share a last common ancestor. He thought about it, but in his Descent of Man and unpublished manuscripts, he clearly places humans as a separate ape clade – gibbons are more closely related to chimps, according to him. Nonetheless, the wonderful nonteleology of this would still have shocked the world at the time: man is just another ape. Like Hume and Kant, Darwin maintained that humans are special because of their sense of morality. But Darwin went further and realised that morality is a product of culture – in a sense, he was applying natural selection to morality. He saw how natives lived in non-European societies and realised that what he considered as moral absolutes could not be applied to those people: you can’t tell an indigenous tribesperson that infanticide is immoral, because they do it routinely out of necessity [Note: this particular example is from Joseph Banks and Tahiti]. To Darwin, morality was a natural consequence of human intelligence and arose biologically through natural selection, and moral norms are not innate biological lines, but ones determined culture and society. This distinction is fundamental and another law of anthropology (no matter what certain neuroscientists say).
On the evolution of flowering plants, Darwin famously called it an “abominable mystery” in a letter to J. D. Hooker (commenting on Ball’s 1879 essay On the origin of the flora of the European Alps, where he also introduces his own theory on angiosperm origins at higher altitudes, where they weren’t fossilised, at times when carbon dioxide levels in the atmosphere were higher [he was assuming that flowering plants can’t stand higher CO2 and that CO2 decreases with altitude]), a phrase that is quoted in every paper and article on the subject. Darwin’s thinking on the subject can be followed to several years earlier than that letter, to correspondence with Swiss botanist, entomologist and palaeontologist Oswald Heer. Heer was proposing that there was very rapid evolution of the flowering plants – in opposition to Darwin’s gradualism. The fossil record at the time was rich in mid- to Late Cretaceous angiosperms, but no Early Cretaceous ones; in other words, they had seemingly appeared ‘immediately’ (much like the animals in the Cambrian). This obviously caused Darwin some unease, as he viewed his notion of evolution as critically dependent on gradualism.
Darwin’s solution to the “abominable mystery” consisted of a “wretchedly poor conjecture”, as he admits to Hooker in the very same letter. Darwin explained it to Heer so: “plants of this great division must have been largely developed in some isolated area, whence owing to geographical changes, they at last succeeded in escaping, and spread quickly over the world”. He thought of some isolated microcontinent on which they were isolated and evolved gradually, before spreading on the continents in the mid-Cretaceous.
The first to think up of co-evolution in the context of angiosperm evolution was French palaeontologist Gaston de Saporta, with whom Darwin also corresponded. Here’s his own explanation of it, from an 1877 letter to Darwin: “You know how the delayed evolution of Dicotyledons has always preoccupied me, as one of the most curious phenomena, as much by its immense importance, as by the apparent speed with which it was formerly manifest. Now, the role that you attribute to Insects in fertilization [pollination, referring to Darwin’s work on orchids and their insect pollinators], coupled with the need for crossing, explains everything: the earlier poverty of the plant kingdom, reduced for so long in the absence of certain categories of insects, to anemophilous plants alone, whose number and diversity were never able to exceed a certain limit, and in which nutritive and succulent substances were never very abundant nor well diversified. The absence of sucking insects during the Jurassic had struck me as well as Mr. Heer. I mentioned this absence or its rarity in my introduction to the Jurassic flora, vol. 1, pp. 53 and 54 …
Now one can conceive very well that the angiosperms, whose floral combinations and crossings of individuals to individuals and of flower to flower depend on the role of insects, could only appear and increase under the impetus of the latter, and the latter for their part, could become numerous and active [as pollinators], and cling to a certain determined type, for which reason the appearance of plants favoured their existence; insects and plants have therefore been simultaneously cause and effect through their connection with each other, plants not being able to diversify without insects and the latter not being able to provide many pollen and nectar feeders so long as the plant kingdom remained poor in arrangements and was composed almost exclusively of anemophilous plants.”
Darwin loved it and recognised its plausibility and importance, replying that “Your idea that dicotyledonous plants were not developed in force until sucking insects had been evolved seems to me a splendid one. I am surprised that the idea never occurred to me, but this is always the case when one first hears a new and simple explanation of some mysterious phenomenon … [Y]our idea, which I hope you will publish, goes much further and is much more important”. Saporta did go on to publish his hypothesis in the 1885 book L’Évolution du Règne Végétal; since then, no other hypothesis has come close to its explanatory power.
Note that Darwin’s “abominable mystery” did not involve homologies between flowering plants and the rest of the plant kingdom, which is what current research is mostly about. He was remarking on the rate of evolution – gradualism vs. saltationism – not the specifics of plant phylogeny. Our fossil record today shows gradual and orderly cladogenesis occurring in the Early Cretaceous – but these findings have only come in the last 30 years. If Darwin were alive right now, his “abominable mystery” would go the way of the birds: just as Archaeopteryx cleared up the mystery of abrupt bird origins, so too would the fossil record of flowers now be gradual enough for Darwin’s liking.
Sexual selection is arguably the second most important discovery that Darwin made – and is undoubtably his own discovery (even if natural selection were plagiarised, sexual selection would have been more than enough for a heaping dose of recognition), although not without controversies. Darwin and Wallace disagreed on evolution by mate choice. Darwin clearly emphasised sexual selection as a process operating distinctly from standard natural selection (females like pretty things, regardless of whether they’re adaptive or not); Wallace’s view dominated though, and stated that sexual selection is just another process within natural selection (females like pretty things, but as long as they’re not harmful in the long run). Darwin’s obsession with sexual selection was somewhat damaging. For example, he attributed human skin colour to sexual selection (humans like smooth skin), rather than the predominant view (since Hippocrates’s times, and proven by John Mitchell and Samuel Stanhope Smith in the mid-18th century) that skin colour is correlated with sunshine; he could very easily have made a point for skin colour as an adaptation to sunshine and added another point of proof for natural selection. However, he had other reasons for not doing so: slavery at the time was accepted due to the underlying notion that dark people were another, inferior species. Darwin was vehemently (and rightly) opposed to this splitting of humans into several species. In any case, sexual selection was rather ignored for a good century and has only recently made a comeback to the forefront of animal behaviour research.
While Darwin is best-known for evolution, he may as well have been a botanist or plant physiologist. He had an early interest in pollination biology, with such statements in letters as “Nothing in my life has ever interested me more than the fertilisation of … plants”. Probably inspired by German botanist Christian Sprengel’s (1750-1816) 1793 book Das entdeckte Geheimnis der Natur, where Sprengel writes that “It appears that nature has not willed that any one flower should be fertilised by its own pollen”, Darwin made many observations of his own on the adaptations plants have against self-fertilisation, knowing full-well from his own domestication experiments the consequences of inbreeding (although that didn’t stop him from marrying his first cousin. ZING!). As a plant physiologist, his 1867 Climbing Plants book established his reputation as a plant biologist. He continued with the theme of plant movements, concluding with his circumnutation theory it is through modification of basic movements that specialised movements (e.g. tropisms) evolved (it’s not a valid theory, but his raw empirical work is excellent; other syntheses, such as his analogy between the root of a plant and the brain of an animal are valid). He was one of the first to realise the importance of light to plant movement and growth. He also devoted two books on insectivorous plants (1875) and flowers (1877).
While these were incorporated into mainstream scientific knowledge of the time, disagreements soon arose. Julius Sachs (1832-1897) disregarded Darwin’s work on the basis of what he perceived as inappropriate experimental protocols (accusations unfounded). Botanist and geneticist Hugo de Vries (1848-1935), Sachs’s student, ended up starting the anti-Darwinian phase of biology of the early 20th century. This had much to do with the fact that Darwin did not discover genetics.
Darwin had no idea about genetics. Yet he also envisioned some sort of particle – a “unit of life” (he termed it a “gemmule”; gemmules worked under the rule of “blending inheritance” – the ones from the parents blended together to form the offspring, hence characters that reappear from grandparents are impossible to explain) that causes “sports” (= mutation) and variation that are the raw material for natural selection. This is rather vague, of course, but the idea of the gene is in there; Mendel’s work was nothing more than the calculation of the mathematical proportions of these “particles of life”; even later, Erwin Schrödinger, in his book What is Life?, speculated on the nature of these “particles of life” and concluded that they were proteins. This succession of thought was finally capped off by Watson, Crick, Wilkins and Franklin’s double helix DNA model. Darwin’s concept seems almost prophetic. In addition to these, he also invoked pangenesis and Lamarckian inheritance of characters according to use and disuse; an example for the latter comes from his observation on cave animals: “it is difficult to imagine that eyes, although useless, could be in any way injurious to animals living in darkness” – he attributes the loss of eyes to disuse, as Lamarckian inheritance would have it.
One could wonder why Darwin never discovered the laws of genetics. After all, in his plant fertilisation experiments, he got the exact same ratios as Mendel did. While the question is ultimately unanswerable (Darwin’s dead, we can’t slap him on the back of his head for being too stupid to think up of it), one reason could be the nature of Darwin’s experiments. In The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom, Darwin was testing whether the progeny produced by self-fertilisation were less fit than those by cross-pollination. While we see it as a classic genetics experiment, for him it was merely a test of survival. He wasn’t trying to figure out what causes the variations in traits, he wanted to know how the traits varied in the first place. He measured seeds, but wasn’t planning on finding out what caused those differences in seed sizes.
Basically, while we nowadays see his experiments as genetically-based, he had no concept of the idea – he couldn’t have had it either. In The Different Forms of Flowers on Plants of the Same Species, we see that Darwin was performing heterozygotic backcrossings. We can determine from his experimental results that dimorphism in Primula is caused by a single locus (actually three closely-linked genes that can’t be separated in his elementary experiments). But this was not Darwin’s goal, and complaining or questioning his intelligence (which is what prompted me to write these couple of paragraphs) is disingenuous. You, as a person living in the 21st century and having basic genetics hammered into your head from basic high school biology, can’t criticise someone 100+ years ago working in the dark for not seeing the results you see. When looking at the work of historical scientists, the first rule is to forget your own education and put yourself in their shoes (unless, of course, you’re comparing their work to today).
Darwin’s theory of natural selection depended on infintessimally small differences that would gradually be selected for or against. He wasn’t interested in the large-scale patterns. He focused on continuous variation, not discontinuous variation. That is no fault of his own though: he searched for what his hypothesis and experiments dictated. One could argue that he needed a unit of inheritance – but he already had his gemmules theory and, to be fair, his concepts of it actually do fit in with his data. As a final point to lay this to rest, Darwin had little education in mathematics, physics and other sciences, unlike Gregor Mendel. This almost definitely played a role. So in summary, don’t read too much into Darwin not having discovered Mendelian genetics even though he had the data in front of him.
In fact, the discovery of genetics was nearly the death of natural selection. The earliest geneticists, such as Hugo de Vries, William Bateson and Richard Goldschmidt, were skeptical of natural selection, instead emphasising the role of mutation. Hugo de Vries conducted experiments, similar to Darwin’s, on flowers and came to the conclusion that evolution is not gradual, but saltational, proceeding by spontaneous mutations. This is what Richard Goldschmidt (1878-1958) used as the basis for his hopeful monsters theory: that a single mutation will produce enormous adaptive changes, rather than the gradual changes that natural selection picked on that Darwin stressed. In fact, until the 1930s, natural selection was pretty much disregarded and semi-supernatural, pseudo-Lamarckian theories dominated – things like organisms having an inner force pushing them towards perfection (e.g. orthogenesis; these views persisted until the 1960s in France and the Soviet Union). So certain were biologists of the time that natural selection was negligible that prominent historian of biology Erik Nordenskiold said in 1929 that natural selection “does not operate in the form imagined by Darwin”; In 1925, a multi-author volume called Evolution in the Light of Modern Knowledge appeared, with zero mention of natural selection. This was the period of anti-Darwinism, spurred on by Darwin’s lack of theory of heritability.
One would think that the rediscovery of Mendelian genetics would have automatically led to reinforcement of Darwinian natural selection. Of course, that statement is another fallacy, as I’m applying my knowledge of the Modern Synthesis to a historical question. Mendel himself knew that evolution was important to understand genetics: “This seems to be the one correct way of finally reaching a solution to a question whose significance for the evolutionary history of organic forms cannot be underestimated”. A review of the historical interplay between genetics and natural selection, while fascinating, is way beyond the scope of this post – suffice it to say it wasn’t until the Modern Synthesis that they were reconciled (see Appendix 2).
Darwin’s emphasis on small variations was controversial. He was a gradualist: small differences slowly accumulate over long periods of time, leading to new species, as he explains in the Origin: “I do believe that natural selection will always act very slowly, often only at long intervals of time, and generally on only a very few of the inhabitants of the same region at the same time. I further believe, that this very slow, intermittent action of natural selection accords perfectly well with what geology tells us of the rate and manner at which the inhabitants of this world have changed.” However, there was an opposing view which gained much more traction was saltationism, whereby new species originated quite suddenly – the discovery of Mendel’s laws were a great boost for them too. People in this group included T. H. Huxley, Francis Galton (Darwin’s cousin) and palaeontologist Othniel C. Marsh. It is outside the scope of this post to go through the whole rates of evolution story, the point is that Darwin’s was not automatically dogmatically accepted as truth, as some would have you believe. In fact, it wasn’t until the Modern Synthesis that saltationism was properly eradicated (although many still clung onto a static species concept). Other differences in opinion include the progressionists: those who viewed evolution as progressing towards a goal (strangely enough, that goal was always bipedal large-brained primates); this group included Ernst Haeckel (great Darwin admirer, although the feeling was apparently not mutual) and Robert Chambers.
Darwin viewed extinction as a by-product of evolution, thus endorsing Georges Cuvier’s view that extinctions were real events – other views of the time included that fossil animals were still alive in unexplored areas of the world (e.g. Thomas Jefferson expected Meriwether Lewis and William Clark to come back from their travels to the interiors of North America with stories of mastodons and mammoths) or that the fossil forms had evolved into the forms of today (Lamarck’s view). While his theory of natural selection cannot say anything on mass extinctions, Darwin invoked biotic interactions (e.g. competition) as the cause for the background extinction rate. While concrete evidence is lacking, some conservation biology studies indicate that competition plays a large role in structuring populations. On the larger scale, this of course means that the oft-cited explanation of macroevolution is microevolution writ large is false. There is a biological filter between the two that shapes macroevolution – this filter could consist mainly of natural selection (but this has not been shown yet).
One thing Darwin got remarkably right was the geographical aspect of extinction. “Humboldt saw in South America a parrot which was the sole living creature that could speak a word of the language of a lost tribe. Ancient monuments and stone implements found in all parts of the world, of which no tradition is preserved by the present inhabitants, indicate much extinction. Some small broken tribes, remnants of former races, still survive in isolated and generally mountainous districts,” he writes in the Descent of Man. This pattern of soon-to-be-extinct populations retreating to remote edges of their former distribution is now well-documented: the extinction force spreads much like a disease and the more isolated a population, the longer it will take to die out.
On the origin of life, Darwin was well aware that his theory had nothing to do with explaining it, despite writing that “all the organic beings which have ever lived on this Earth may be descended from some primordial form.” In 1839, he wrote that his “theory leaves quite untouched the question of spontaneous generation” and in a letter to the physician George Charles Wallich, he honestly states that he “had intentionally left the question of the Origin of Life uncanvassed as being altogether ultra vires in the present state of information”. This attitude was lambasted by both critics and supporters. Ernst Haeckel, Darwin’s main cheerleader in Germany, wrote in 1862 that Darwin “assumes a special creative act for this first species, he is not consistent, and, I think, not quite sincere”. Some did go a bit far though: George Heinrich Bronn, the geologist who translated the Origin into German, simply added a chapter describing how natural selection leads to the origin of life. Darwin was not impressed with this, writing to Lyell in 1860 that “He [Bronn] sticks to Priestley’s green matter & seems to think that till it can be shown how life arises, it is no good showing how the forms of life arise. This seems to me about as logical (comparing very great things with little) as to say it was no use in Newton showing laws of attraction of gravity & consequent movements of the Planets, because he could not show what the attraction of Gravity is”.
His own view on the subject is well-known from a letter he sent to Hooker in 1871:
It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present. But if (and oh! What a big if) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, &c., present, that a protein compound was chemically formed ready to undergo still more complex changes, at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.” In other words, the same scenario many origin-of-life researchers still consider nowadays (although many, many alternatives exist). As time progressed, Darwin thought more and more about the origin of life, but ultimately came to the conclusion that while it was an important question that could be answered scientifically, science had not advanced to that point yet, writing in the The Variation of Animals and Plants under Domestication that “As the first origin of life on this earth, as well as the continued life of each individual, is at present quite beyond the scope of science, I do not wish to lay much stress on the greater simplicity of the view of a few forms, or of only one form, having been originally created, instead of innumerable miraculous creations having been necessary at innumerable periods; though this more simple view accords well with Maupertuis’s philosophical axiom ‘of least action’.
The origin of life debate in Darwin’s time was (somewhat surprisingly) as heated as it is today, but dominated by the notion of ‘spontaneous generation’, which was as vague back then as it is today. The most prominent origin-of-life scientist back then, Henry Charlton Bastian, differentiated between two forms of spontaneous generation: archebiosis, the “origin of living things from non-living materials” and heterogenesis, “the possibility of living things arising by previously unknown methods from the matter of pre-existing living things”. Darwin, after reading Bastian’s 1872 The Beginning of Life, wrote to Wallace saying “His [Bastian’s] general argument in favour of Archebiosis is wonderfully strong, though I cannot think much of some few of his arguments. The result is that I am bewildered and astonished by his statements, but am not convinced, though, on the whole, it seems to me probable that Archebiosis is true”. However, on receiving Haeckel’s The History of Creation, wherein Haeckel endorsed spontaneous generation, Darwin wrote back to Haeckel saying “I will at the same time send a paper which has interested me; it need not be returned. It contains a singular statement bearing on so-called Spontaneous Generation. I much wish that this latter question could be settled, but I see no prospect of it. If it could be proved true this would be most important to us”.
Memorably, Richard Owen published a book review in which he claimed that foraminifera and other microorganisms can spontaneously arise from mud and blasted Darwin (they never were on good terms, those two) for bringing in the Creator as the source of life (the last paragraph of the Origin). You have already read what Darwin immediately thought of Owen’s criticism – I quoted it several paragraphs ago when I mentioned the Creator line. Darwin then published a fuller response and published it in the same magazine that Owen published his review in (The Athenaeum). I will quote this in full, because it completely summarises Charles Darwin’s thoughts on the origin of life, more extensively than his “warm little pond” letter he sent to Hooker 8 years later. It’s also, in my opinion, one of the most elegant of Charles Darwin’s responses to criticism, with gentlemanly rebukes, delicious irony and packed full of logic and evidence.
I hope that you will permit me to add a few remarks on Heterogeny, as the old doctrine of spontaneous generation is now called, to those given by Dr. Carpenter [author of the book Owen was reviewing], who, however, is probably better fitted to discuss the question than any other man in England. Your reviewer [Richard Owen] believes that certain lowly organized animals have been generated spontaneously — that is, without pre-existing parents — during each geological period in slimy ooze. A mass of mud with matter decaying and undergoing complex chemical changes is a fine hiding-place for obscurity of ideas. But let us face the problem boldly. He who believes that organic beings have been produced during each geological period from dead matter must believe that the first being thus arose. There must have been a time when inorganic elements alone existed on our planet: let any assumptions be made, such as that the reeking atmosphere was charged with carbonic acid, nitrogenized compounds, phosphorus, &c. Now is there a fact, or a shadow of a fact, supporting the belief that these elements, without the presence of any organic compounds, and acted on only by known forces, could produce a living creature? At present it is to us a result absolutely inconceivable. Your reviewer sneers with justice at my use of the “Pentateuchal terms”, “of one primordial form into which life was first breathed”: in a purely scientific work I ought perhaps not to have used such terms; but they well serve to confess that our ignorance is as profound on the origin of life as on the origin of force or matter. Your reviewer thinks that the weakness of my theory is demonstrated because existing Foraminifera are identical with those which lived at a very remote epoch. Most naturalists look at this fact as the simple result of descent by ordinary reproduction; in no way different, as Dr. Carpenter remarks, except in the line of descent being longer, from that of the many shells common to the middle Tertiary and existing periods.
The view given by me on the origin or derivation of species, whatever its weaknesses may be, connects (as has been candidly admitted by some of its opponents, such as Pictet, Bronn, &c.) by an intelligible thread of reasoning a multitude of facts: such as the formation of domestic races by man’s selection, the classification and affinities of all organic beings, the innumerable gradations in structure and instincts, the similarity of pattern in the hand, wing or paddle of animals of the same great class, the existence of organs become rudimentary by disuse, the similarity of an embryonic reptile, bird and mammal, with the retention of traces of an apparatus fitted for aquatic respiration; the retention in the young calf of incisor teeth in the upper jaw, &c., the distribution of animals and plants, and their mutual affinities within the same region, their general geological succession, and the close relationship of the fossils in closely consecutive formations and within the same country; extinct marsupials having preceded living marsupials in Australia, and armadillo-like animals having preceded and generated armadilloes in South America, and many other phenomena, such as the gradual extinction of old forms and their gradual replacement by new forms better fitted for their new conditions in the struggle for life. When the advocate of Heterogeny can thus connect large classes of facts, and not until then, he will have respectful and patient listeners.
Dr. Carpenter seems to think that the fact of Foraminifera not having advanced in organization from an extremely remote epoch to the present day is a strong objection to the views maintained by me. But this objection is grounded on the belief — the prevalence of which seems due to the well-known doctrine of Lamarck — that there is some necessary law of advancement, against which view I have often protested. Animals may even become degraded, if their simplified structure remains well fitted for their habits of life, as we see in certain parasitic crustaceans. I have attempted to show (Origin, 3rd edit. p. 135) that lowly-organized animals are best fitted for humble places in the economy of nature; that an infusorial animalcule or an intestinal worm, for instance, would not be benefited by acquiring a highly complex structure. Therefore, it does not seem to me an objection of any force that certain groups of animals, such as the Foraminifera, have not advanced in organization. Why certain whole classes, or certain numbers of a class, have advanced and others have not, we cannot even conjecture. But as we do not know under what forms or how life originated in this world, it would be rash to assert that even such lowly endowed animals as the Foraminifera, with their beautiful shells as figured by Dr. Carpenter, have not in any degree advanced in organization. So little do we know of the conditions of life all around us, that we cannot say why one native weed or insect swarms in numbers, and another closely allied weed or insect is rare. Is it then possible that we should understand why one group of beings has risen in the scale of life during the long lapse of time, and another group has remained stationary? Sir C. Lyell, who has given so excellent a discussion on species in his great work on the ‘Antiquity of Man’, has advanced a somewhat analogous objection, namely, that the mammals, such as seals or bats, which alone have been enabled to reach oceanic islands, have not been developed into various terrestrial forms, fitted to fill the unoccupied places in their new island-homes; but Sir Charles has partly answered his own objection. Certainly I never anticipated that I should have had to encounter objections on the score that organic beings have not undergone a greater amount of change than that stamped in plain letters on almost every line of their structure. I cannot here resist expressing my satisfaction that Sir Charles Lyell, to whom I have for so many years looked up as my master in geology, has said (2nd edit. p. 469): “Yet we ought by no means to undervalue the importance of the step which will have been made, should it hereafter become the generally received opinion of men of science (as I fully expect it will) that the past changes of the organic world have been brought about by the subordinate agency of such causes as Variation and Natural Selection”. The whole subject of the gradual modification of species is only now opening out. There surely is a grand future for Natural History. Even the vital force may hereafter come within the grasp of modern science, its correlations with other forces have already been ably indicated by Dr. Carpenter in the Philosophical Transactions; but the nature of life will not be seized on by assuming that Foraminifera are periodically generated from slime or ooze.
Pwnd. So, to summarise Darwin’s thoughts: he had no mystical view of the origin of life, his view being that “The intimate relation of Life with laws of chemical combination, & the universality of latter render spontaneous generation not improbable,” but he remained realistic, knowing full well that his “theory leaves quite untouched the question of spontaneous generation,” and that “though I expect that at some future time the principle of life will be rendered intelligible, at present it seems to me beyond the confines of science,” and he knew that “I should like to live to see Archebiosis proved true, for it would be a discovery of transcendent importance; or, if false, I should like to see it disproved, and the facts otherwise explained; but I shall not live to see all this.” (All these are Darwin’s words from various letters.)
Finally, what Darwin thought of panspermia – also popular at the time – is not known, although he most likely scoffed at the idea. His friend Joseph Hooker certainly found it ridiculous, writing in 1871 that he “would as soon believe in the Phoenix as in the meteoritic import of life”.
Since I still haven’t actually said anything about Joseph Hooker, although I have mentioned him several times as Darwin’s penpal, here’s a short sketch of him. He was a botanist, the director of the Royal Botanical Gardens in Kew. He was one of Darwin’s closest friends and a staunch defender of his theory. He was the one who identified and classified Darwin’s collected plants from the Beagle voyage, naming many new taxa. He recognised similarities between the floras of South America and Australia and posited that the two continents were once joined by a now-flooded land bridge.
Speaking of origin of life, Darwin never once mentions bacteria in any of his books. It was Ernst Haeckel and Russian biologist Constantin S. Mereschkowsky (1855-1921; originator of the symbiosis concept) who first thought to put the microorganisms on the tree of life.
Speaking of the tree of life, many seem to think that it was Darwin’s original metaphor. It isn’t. Peter Simon Pallas (1741-1811) was actually the first to use a tree of life to portray the system of nature in 1787. It’s a rather contradictory account though: the text presents nature as a traditional Biblical unchanging body, while the figure contains some striking transformational ideas – one would term them pre-evolutionary. Lamarck also used trees to illustrate his concepts.
This brings us to what is Darwin’s truly greatest contribution to biology. Natural selection and sexual selection are processes and mechanisms that were waiting to be discovered and have been so revolutionised in the time since Darwin that were he alive now, he wouldn’t recognise an evolutionary biology textbook if you slapped him with it. The truly enduring contribution that Darwin made was paradigmical. It was a change in how we think, namely in terms of genealogy, or tree-thinking (see the picture above, which is the only picture found in the Origin). Sure, Jean-Baptiste Lamarck and the other pre-Darwinian evolutionists had notions of it, but Darwin was the one who explicitly injected it into biology – this was the true Darwinian revolution. Before him, biologists were looking for laws and types. Organisms were viewed as deviations from a Bauplan, or an ideal form, and it was this that pre-Darwinian systematists tried to reconstruct. After Darwin, this was rendered obsolete. Organisms were not flawed ideals, but were the result of a long historical development, partly recorded by the geological and fossil records. This underlies our phylogenetic thinking today: whales are mammals, not flawed fish; birds are dinosaurs; octopi are molluscs – all of these would not have been recognised as such before Darwinian genealogical thinking. We stopped asking “What is the true nature of a structure” and started asking “What was the previous state of a structure”. Before him, diversity was the result of Newtonian (mechanical) transformations; after him, diversity was the result of history. Immutable Newtonian laws were not enough to explain life – there was something more acting on organisms. That something was natural selection. The memorable debate between Étienne Geoffroy Saint-Hilaire and Georges Cuvier was now resolved. Cuvier argued that function determines form, Saint-Hilaire the opposite. Darwinian genealogical thinking shows that neither are wrong: form and function have been inextricably woven together by history.
The old notion of a scala naturae was also effectively out of the realm of biology. There was no such thing as a gradation from simple to complex organism; as Darwin stressed, from then on, we could “Never use the words higher or lower” when referring to organisms; instead we speak of ancestral or derived characters.
This example brings up another popular discussion in evolutionary biology: adaptationism. Evolutionary psychologists stress that every single behaviour has an evolutionary reason behind it – if you like sleeping near the door, it’s because your male ancestors slept at the entrance of the cave to protect it. Others say that there are no adaptations, but merely the results of controlled genetic drift. Of course, both these views are too extreme. Darwin himself thought genealogically: something is adaptive if it has been kept through generations – the null hypothesis is that a feature is not adaptive. This is, of course, correct. In other words, Darwin already had a concept of the neutral trait – although he did find it rather troubling for his theory: how could these traits have evolved if they weren’t selected for? (Answer: they were selected for at some point in the past!)
Another thing Darwin listed as troubling for his theory was altruism, especially the sterile workers of eusocial insect colonies, who sacrifice their reproductive lives in order for the queen to reproduce. He invoked group selection, specifically colony-level selection, to explain altruism: those groups with fewer altruists were ultimately less competitive than those with more altruists.
“Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely-graduated organic chain; and this, per- haps, is the most obvious and serious objection which can be urged against the theory.” In this quote from the Origin, Darwin is lamenting the incompleteness of the fossil record as it was known to him – although almost a hundred pages later, he states “Passing from these difficulties, all the other great leading facts in palaeontology seem to me simply to follow on the theory of descent with modification through natural selection”. Darwin’s stance on the fossil record is not as contradictory as it may appear. In the former quote, from Chapter 9 (“On the Imperfection of the Geological Record”), he’s arguing that the fossil record does not show any gradual changes as predicted by his theory – although the finding of Archaeopteryx may have changed his mind about that later on. In the second quote, he is looking at the fossil record broadly, and from that vantage point, it became clear that it does support his theory of natural selection – but the resolution is too low to be able to zoom in. Of course, this view is ridiculous to hold nowadays, but at his time, it was perfectly reasonable given the state of palaeontological research.
One field most people (unpublished data from my own unscientific polling) don’t know that Darwin researched is pedology. That’s soil science. He was one of the first to scientifically quantify the importance of earthworms in soil production, observing how the fertile topsoil is mostly made from earthworm casts and calculating soil turnover rates at his house over 30 years (cobbles he placed in his garden) and centuries (Roman and Druidal artifacts in the soil) – the first to produce such a study.
All that said, why should anyone who’s not a biologist care about Darwin? Since the Stone Age, humans have been fascinated by animals and their “endless forms most beautiful”. We have long recognised that these animal forms are classifiable, that there is unity in all this diversity. We have long sought to explain why this diversity exists – why are there whales and snails? The answer was given to us by Charles Darwin and his theory of natural selection. This is why he deserves our recognition.
And if human curiosity and satisfaction isn’t your thing, his work also laid the foundation for truly understanding agriculture, medicine and SUPERBUGS. Without his work, you’d probably be dead now. :)
As a final note, to address a possible concern pointed out to me by someone who read this before it was posted. This post, just by its length, is enough praise for Darwin. I will not proverbially suck his cock – I have written nice things about the guy, how he has revolutionised biology and our modern society. The points in criticism are not to be taken as negatives, they’re to be taken as updates. He was a great guy and all, but a lot has happened in the past one and a half centuries. The concept of evolution has evolved. If anything, my few critical points are more points of praise for Darwin’s genius: he made us realise that evolution occurs in the first place, and the fact that we can still meaningfully discuss and argue the concepts he introduced over 150 years ago is testament to how important his legacy is. And that legacy lives on and we are actively fulfilling Darwin’s hopes for the future, as expressed in this 1857 letter to T. H. Huxley: “The time will come I believe, though I shall not live to see it, when we shall have very fairly true genealogical trees of each great kingdom of nature.”
In fact, no higher praise is possible for Darwin once you realise the fact that uniquely in all the sciences, the Origin of Species remains one of the foundational required reading books for any biologist 150 years after its publication. Or if that’s not enough, how about the need of evolutionary biologists to classify their theories as “Darwinian”, “ultra-Darwinian”, “anti-Darwinian”, “Neodarwinian”, “Postneodarwinian”, etc. (see Appendix 2)? I, for one, have never heard of an Einsteinian theory of quantum physics; Newton has that priviledge (Newtonian mechanics), as does Mendel (Mendelian genetics). Such is Darwin’s work’s foresight and timelessness that one and a half centuries later, we still measure our theories according to the standards that he set. In other words, The Origin is not a fossil but is still very much under discussion (especially since the Modern Synthesis missed many points about it!). Even sentences he wrote incidentally, e.g. the “warm little pond”, are being pored over to this day. A short literature survey reveals 36 species named after Darwin. So yeah, I doubt my dinky little post will do much insult to his name, even if I had wanted it to.
Appendix 1: Malthusian rule, from his Essay on the Principle of Population (1798)
“The power of population is indefinitely greater than the power of the earth to produce subsistence for man. Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio. …
By that law of our nature which makes food necessary for the life of man, the effects of these two unequal powers must be kept equal. This implies a strong and constantly operating check on population from the difficulty of subsistence.
This difficulty must fall somewhere and must necessarily be severely felt by a large portion of mankind.”
Appendix 2: -“Darwinism”
As a reference, Darwinism (or Darwinian evolution) is a short form for six theories, the first five published in the Origin, the last in the Descent of Man.
- Species evolve and are not static in time.
- Species are descended from a common ancestor.
- Over time, diverged species will accumulate differences in appearance.
- Gradualism, i.e. that these changes take place in small steps, in contrast to saltationism.
- Natural selection, a mechanism that selects for only the best adapted individuals to survive. As a sidenote, this has often been cited as a tautology (a tradition started by Karl Popper in 1975, but he took it back in 1978). The misunderstanding stems from a conception of evolution having a direction, when in fact it does not (and Darwin never said it did).
- Sexual selection, that competition between sexes is also a force for evolution.
Neodarwinism is just another name for the Modern Synthesis, also called the Synthetic Theory of Evolution, New Synthesis or Neodarwinian Synthesis. However, “neodarwinism” as a term was first put forward by George John Romanes to describe Alfred Russel Wallace’s evolutionary theory (the difference was that Wallace rejected Lamarckian inheritance, while Darwin accepted it). In those times, August Weismann was the most prominent neodarwinist; Weismann was the first to show the difference between germ and somatic cells, thereby showing that in animals, Lamarckianism is impossible. However,neodarwinism is now associated with the concepts that Julian Sorell Huxley and Ernst Mayr put forward in the 1940s, namely the unification of Darwinism, developmental and cell biology, Mendelian genetics, population genetics (from Ronald Aylmer Fisher, John Burdon Sanderson Haldane and Sewall Wright), phylogenetics and palaeontology (from George Gaylord Simpson).
Anon. 1880. What Mr. Darwin Saw In His Voyage Round The World in the Ship ‘Beagle’.
Browne, J. 2005. Presidential address: commemorating Darwin. British Journal for the History of Science 38, 251-274.
Darwin, F. (ed.). 1887. The Life and Letters of Charles Darwin, Including an Autobiographical Chapter, 3rd ed., vol. 1.
Davies, R. 2008. The Darwin Conspiracy.
Gorbushina, A. A., Kort, R., Schulte, A., Lazarus, D., Schnetger, B., Brumsack, H.J., Broughton, W. J. & Favet, J. 2007. Life in Darwin’s dust: intercontinental transport and survival of microbes in the nineteenth century. Environmental Microbiology 9, 2911-2922.
Gregory, T. R. 2009. Understanding Natural Selection: Essential Concepts and General Misconceptions. Evolution: Education and Outreach 2, 156-175.
Mayr, E. 1963. Animal Species and Evolution.
Wainwright, M. 2010. The origin of species without Darwin and Wallace. Saudi Journal fo Biological Sciences 17, 187-204.