The Invention of Nature

17

Evolution and Nature

Charles Darwin and Humboldt

HMS BEAGLE WAS riding the valleys and crests of the waves with relentless regularity as the wind ruffled the swelling canvas of the sails. The ship had left Portsmouth on the south coast of England four days previously, on 27 December 1831, on a voyage across the globe to survey coastlines and measure the exact geographical positions of ports. On board was twenty-two-year-old Charles Darwin who felt ‘wretchedly out of spirits’. This was not how he had envisaged his adventure. Instead of standing on deck and watching the wild sea as they crossed the Bay of Biscay towards Madeira, Darwin was feeling more miserable than he ever had before. He was so seasick that the only way to bear it was to hide out in his cabin, eat dry biscuits and remain horizontal.

The small poop cabin that he shared with two crew members was so crammed that his hammock was strung above the table where the officers worked on sea charts. The cabin was about ten by ten feet, lined with bookshelves, lockers and a chest of drawers along the walls and the large surveying table in the middle. At around six feet tall, Darwin didn’t have the headroom to stand. Cutting through the midst of the small space was the ship’s mizzenmast like a large column next to the table. To move around in the cabin the men had to clamber over the bulky wooden beams of the ship’s steering gear which crossed the floors. There was no window, only a skylight through which Darwin watched the moon and the stars as he lay in his hammock.

On the small shelf next to his hammock were Darwin’s most precious possessions: the books that he had carefully chosen to accompany him. He had a number of botanical and zoological volumes, a brand-new Spanish–English dictionary, several travel accounts written by explorers and the first volume of Charles Lyell’s revolutionary Principles of Geology which had been published the previous year. Next to it was Alexander von Humboldt’s Personal Narrative, the seven-volume account of the Latin American expedition and the reason why Darwin was on the Beagle.¹ ‘My admiration of his famous personal narrative (part of which I almost know by heart),’ Darwin said, ‘determined me to travel in distant countries, and led me to volunteer as naturalist in her Majesty’s ship Beagle.’

Plan of the Beagle with Darwin’s cabin (poop deck) towards the stern (Illustration Credit 17.1)

Weakened by nausea, Darwin began to doubt his decision. When they passed Madeira on 4 January 1832, he felt so ill that he couldn’t even bring himself to stumble on deck to see the island. Instead he was inside, reading Humboldt’s descriptions of the tropics because nothing was better ‘for cheering the heart of a sea-sick man’, he said. Two days later they reached Tenerife – the island Darwin had dreamed of for many months. He wanted to walk among slender palms and see Pico del Teide, the 12,000-foot volcano that Humboldt had climbed more than three decades previously. As the Beagle neared the island, a boat stopped them and it was announced that they weren’t allowed to go ashore. The authorities in Tenerife had heard of recent cholera outbreaks in England and worried that the sailors might bring the disease to the island. When the consul imposed a twelve-day quarantine, the Beagle’s captain decided to press on rather than wait. Darwin was devastated. ‘Oh misery, misery,’ he wrote in his journal.

That night, as the Beagle sailed away from Tenerife, the sea calmed. As gentle waves rolled in against the ship’s stern and the warm air softly flapped the sails, Darwin’s nausea lessened. The sky was scrubbed clean and uncountable stars spread their glitter across the dark mirrored water. It was a magical moment. ‘Already can I understand Humboldts enthusiasm about the tropical nights,’ Darwin wrote. Then, the next morning, as he watched the cone-shaped Pico del Teide disappearing in the distance, tinged in orange sunlight and its peak poking out above the clouds, he felt repaid for his sickness. Having read so much about the volcano in Personal Narrative, he said, it was ‘like parting from a friend’.

Only a few months previously the prospect of seeing the tropics and of being the naturalist on an expedition had been the ‘wildest Castles in the air’ for Darwin. According to his father’s wishes he had been destined for a more conventional profession and had studied at Cambridge to become a country clergyman. This choice had been a compromise to pacify his father after Darwin had abandoned his medical studies at Edinburgh University. Convinced that he would one day inherit enough money to ‘subsist with some comfort’, Darwin had not been too ambitious about his prescribed career. In Edinburgh he had preferred to examine marine invertebrates rather than focus on his medical work, and in Cambridge he had attended botanical lectures instead of those required for theology. He had become fascinated by beetles and went on long walks, lifting stones and logs, stuffing his bags with his entomological treasures. Never wanting to lose any of his finds, one day – with his hands already full of beetles – he had even popped one in his mouth for safekeeping. The beetle objected to this unusual treatment, ejecting enough acid fluid for Darwin to spit it out.

It was during his last year in Cambridge that Darwin first read Humboldt’s Personal Narrative, a book that ‘stirred up in me a burning zeal’, he wrote. Darwin was so impressed by Humboldt’s writing that he copied out passages and read them aloud to his botany teacher, John Stevens Henslow, and other friends during their botanical excursions. By spring 1831, Darwin had studied Humboldt so intensely that ‘I talk, think, & dream of a scheme I have almost hatched of going to the Canary Islands,’ he told his cousin.

His plan was to travel to Tenerife with Henslow and some university friends. Darwin was so excited, he said, that ‘I cannot hardly sit still.’ In preparation he dashed to the hothouses in the botanical garden in Cambridge in the mornings to ‘gaze at the Palm trees’ and then rushed home to study botany, geology and Spanish. Dreaming of dense forests, dazzling plains and mountaintops, he ‘read and reread Humboldt’ and talked so much about the trip that his friends in Cambridge began to wish he had already left. ‘I plague them,’ Darwin joked to his cousin, ‘with talking about tropical scenery.’

In mid-July 1831 Darwin reminded Henslow to read more Humboldt ‘to fan your Canary ardor’. His letters gushed with excitement and were peppered with newly learned Spanish expressions. ‘I have written myself into a Tropical glow,’ he told his sister. But then, just as they were preparing to leave, Henslow cancelled because of work commitments and his wife’s pregnancy. Darwin also realized that few British ships sailed to the Canary Islands – and those few only in the early summer months. They were too late in the season, and he would have to defer the trip to the following year.

Charles Darwin (Illustration Credit 17.2)

Then, a month later, on 29 August 1831, everything changed when Darwin received a letter from Henslow. A certain Captain Robert FitzRoy, Henslow wrote, was looking for a gentleman naturalist to travel as his companion on the Beagle – a ship that was due to leave four weeks later on a circumnavigation of the globe. This was a much more exciting prospect than Tenerife. But Darwin’s enthusiasm was immediately dampened when his father refused his permission and the much needed financial assistance to pay for his son’s passage. It was ‘a wild scheme’, Robert Darwin told his son, and a ‘useless undertaking’. A voyage across the globe didn’t seem a necessary prerequisite for being a country clergyman.

Darwin felt crushed. Of course the voyage would not be cheap but his family could afford it. His father was a successful doctor who had made most of his money as a canny investor, and Darwin’s grandfathers had made the family famous and prosperous. The celebrated potter Josiah Wedgwood was his maternal grandfather – a man who had applied science to manufacturing and thereby industrialized the production of chinaware. Wedgwood had died a rich and respected man. Charles Darwin’s paternal grandfather, the physician, scientist and inventor Erasmus Darwin, was equally illustrious. In 1794 he had published the first radical evolutionary ideas in his book Zoomania in which he had claimed that animals and humans descended from tiny living filaments in the primordial sea. He had also turned Carl Linnaeus’s botanical classification system into verse in his hugely popular poem Loves of the Plants – which Humboldt and Goethe had read in the 1790s. There was a pride of achievement in the family, maybe even a sense of greatness, to which Charles Darwin certainly also aspired.

In the end it was an uncle who helped to convince Darwin’s father of the value of the trip. ‘If I saw Charles now absorbed in professional studies,’ Josiah Wedgwood II wrote to Robert Darwin, it would not be advisable to interrupt them, ‘but this is not, and I think will not be, the case with him’. Since Charles was only interested in natural history, his uncle concluded, the expedition would be a great opportunity to leave his mark in the world of science. The next day Darwin’s father finally agreed to underwrite his son’s expenses. Darwin was to go around the world.

The first three weeks of the voyage, as the Beagle sailed south, were rather uneventful. After they had passed Tenerife, Darwin was feeling better. As the days became warmer, he changed into lighter clothes. Darwin caught jellyfish and other small marine invertebrates, occupying himself with dissecting them. It was also a good time to get to know the rest of the crew. Darwin shared his cabin with the nineteen-year-old assistant surveyor and one of the midshipmen who was fourteen at the time. There were seventy-four men on board, including sailors, carpenters and surveyors as well as an instrument maker, an artist and a surgeon.² At twenty-six, Captain FitzRoy was only four years older than Darwin. He came from an aristocratic family and had spent all his adult life at sea. This was his second voyage on the Beagle. As the crew quickly discovered, the captain could be bad-tempered and morose – especially in the early mornings. With an uncle who had committed suicide, FitzRoy often worried that he might be prey to similar predispositions. At times, the captain fell into deep depressions that were ‘bordering on insanity’, Darwin thought. FitzRoy alternated between seemingly boundless energy and silent melancholy. But he was intelligent, fascinated by natural history and worked incessantly.

FitzRoy was heading a government-funded expedition with the goal of circumnavigating the globe to make a full circle of longitudinal measurements – using the same instruments in an attempt to standardize maps and navigation. He had also been instructed to complete a survey of the southern coast of South America where Britain hoped to gain economic dominance among the newly independent South American nations.

At ninety feet long, the Beagle was a small ship, but packed to the rim – from thousands of tin cans filled with preserved meat to the latest surveying instruments. FitzRoy had insisted on taking as many as twenty-two chronometers to measure time and longitude, as well as lightning conductors to protect the ship. The Beagle carried sugar, rum and dried peas as well as the usual remedies against scurvy such as pickles and lemon juice. ‘The hold would contain scarcely another bag of bread,’ Darwin noted in admiration about the tight packing.

The Beagle’s first landfall was at Santiago, the largest of the Cape Verde islands in the Atlantic Ocean, some 500 miles off the western coast of Africa. Stepping ashore on to the tropical island, new impressions rushed into Darwin’s mind. It was confusing, exotic and thrilling. Palms, tamarind and banana trees vied for his attention, as did the bulbous baobab tree. He heard the melodies of unfamiliar birds, and saw strange insects settling into the blooms of even stranger flowers. Like Humboldt and Bonpland on their arrival in Venezuela in 1799, Darwin’s mind was a ‘perfect hurricane of delight & astonishment’ as he examined volcanic rocks, pressed plants, dissected animals and pinned moths. As Darwin hacked off rocks, scraped off bark and looked for insects and worms under stones, he collected everything from shells and huge palm tree leaves to flatworms and the tiniest insects. In the evenings, when he returned, ‘heavily laden with my rich harvest’, he couldn’t have been happier. Darwin was like a child with a new toy, Captain FitzRoy laughed.

It was ‘like giving to a blind man eyes’, Darwin wrote in his journal. To describe the tropics was impossible, he explained in his letters home, because it was all so different and bewildering that he felt at a loss how to begin or end a sentence. He advised his cousin William Darwin Fox to read Humboldt’s Personal Narrative to understand what he was experiencing and told his father, ‘if you really want to have a notion of tropical countries study Humboldt.’ Darwin was seeing this new world through the lens of Humboldt’s writing. His diary was filled with comments such as ‘much struck by the justness of one of Humboldt’s observations’ or ‘as Humboldt remarks’.

There was only one other publication that shaped Darwin’s mind to a similar extent and that was Charles Lyell’s Principles of Geology, a book that itself was steeped in Humboldt’s ideas. In it Lyell quoted Humboldt dozens of times, ranging from his idea of global climate and vegetation zones, to information about the Andes. In Principles of Geology Lyell explained that the earth had been shaped by erosion and deposition in a series of very slow movements of elevation and subsistence over an unimaginably long period of time, punctuated by volcanic eruptions and earthquakes. As Darwin looked at the rock strata along the cliffs of Santiago, everything that Lyell had written made sense to him. Here Darwin could ‘read’ the creation of the island by looking at the layers of the sea cliffs: the remains of an old volcano, then further up a white band of shells and corals and above that a layer of lava. The lava had covered the shells and since then the island had been slowly pushed up by some subterranean force. The undulating line and irregularities of the white band were also testimony to more recent movement – Lyell’s forces that were still active. As Darwin rushed across Santiago, he saw the plants and animals through Humboldt’s eyes and the rocks through Lyell’s. When Darwin returned to the Beagle, he wrote a letter to his father, announcing that inspired by what he had seen on the island ‘I shall be able to do some original work in Natural History.’

A few weeks later, when the Beagle reached Bahia (today’s San Salvador) in Brazil at the end of February, Darwin’s amazement continued. Everything was so dream-like that it might have been a magical scene in the Arabian Nights, he explained. Again and again, he wrote that only Humboldt came close to describing the tropics. ‘My feelings amount to admiration the more I read him,’ he declared in one letter home, and ‘I formerly admired Humboldt, I now almost adore him’ in another. Humboldt’s descriptions were unparalleled, he said on the day he saw Brazil for the first time, because of the ‘rare union of poetry with science’.

He was walking in a new world, Darwin wrote to his father. ‘I am at present red-hot with Spiders,’ he exulted, and the flowers would ‘make a florist go wild’. There was so much that he wasn’t sure what to look at or pick up first – the gaudy butterfly, the insect crawling into an exotic bloom or a new flower. ‘I am at present fit only to read Humboldt,’ Darwin wrote in his journal, for ‘he like another Sun illumines everything I behold.’ It was as if Humboldt gave him a rope on which to hold tight so as not to drown in these new impressions.

The Beagle sailed south to Rio de Janeiro and Montevideo, and then on to the Falkland Islands, Tierra del Fuego and Chile – over the course of the next three and a half years often retracing the route to ensure the accuracy of their survey. Darwin regularly took leave from the ship for several weeks at a time to go on long inland excursions (having arranged with FitzRoy where to rejoin the Beagle). He rode through the Brazilian rainforest and joined the gauchos in the Pampas. He saw the wide horizons over the dusty plains of Patagonia and found giant fossil bones at the coast of Argentina. He had become, he wrote to his cousin Fox, ‘a great wanderer’.

When he was on board the Beagle, Darwin followed a routine that never changed much. In the mornings he joined FitzRoy for breakfast and then both men turned to their respective tasks, the captain surveying and dealing with his paperwork while Darwin investigated his specimens and wrote up his notes. Darwin worked in the poop cabin at the big chart table where the assistant surveyor also had his maps. In one corner Darwin had set up his microscope and notebooks. There he dissected, labelled, preserved and dried his specimens. The space was cramped but he thought it was the perfect study for a naturalist because ‘everything is so close at hand’.

Outside on deck the fossil bones had to be cleaned and jellyfish had to be caught. In the evenings, Darwin shared his meals with FitzRoy but once in a while he was invited to join the rest of the crew in the more boisterous mess-room which he always enjoyed. With the Beagle sailing up and down the coast working on the survey, there was plenty of fresh food available. They ate tuna, turtle and shark, as well as ostrich dumplings and armadillos which, Darwin wrote home, without their armoured shells looked and tasted just like duck.

Darwin adored his new life. He was popular with the crew who called him ‘Philos’ and ‘flycatcher’. His passion for nature was infectious and soon many of the others became collectors too, helping to augment his specimens. One officer teased him about the ‘damned beastly bedevilment’ of barrels, crates and bones on deck, saying that ‘if I were the skipper, I would soon have you and all your mess out of the place.’ Whenever they arrived at a trading port from where vessels were sailing to England, Darwin would dispatch his trunks filled with fossils, bird skins and pressed plants to Henslow in Cambridge, as well as sending letters home.

As they sailed on, Darwin felt even more urgently the need to read everything that Humboldt had written. When they reached Rio de Janeiro, in April 1832, he had written home, asking his brother to send Humboldt’s Views of Nature to Montevideo in Uruguay where he would be able to pick it up at a later stage. His brother duly sent books – not Views of Nature but Humboldt’s latest publication Fragmens de géologie et de climatologie asiatiques which was the result of the Russian expedition, as well as the Political Essay on the Kingdom of New Spain.

Throughout the Beagle’s voyage, Darwin was engaged in an inner dialogue with Humboldt – pencil in hand, highlighting sections in Personal Narrative. Humboldt’s descriptions were almost like a template for Darwin’s own experiences. When Darwin first saw the star constellations of the southern hemisphere, he was reminded of Humboldt’s descriptions. Or later when he saw the Chilean plains after days of exploring the untamed forest, Darwin’s reaction exactly echoed Humboldt’s on entering the Llanos in Venezuela after the Orinoco expedition. Humboldt had written of ‘new sensations’ and the delight of being able to ‘see’ again after the long weeks in the dense rainforest, and now Darwin described how the views were ‘very refreshing, after being hemmed in & buried amongst the wilderness of trees’.

Similarly, Darwin’s diary entry about an earthquake that he experienced on 20 February 1835, in Valdivia in southern Chile, was almost a summary of what Humboldt wrote about his first earthquake in Cumaná in 1799. Humboldt had remarked how the earthquake in ‘one instant is sufficient to destroy long illusions’ – in Darwin’s journal it became ‘an earthquake like this at once destroys the oldest associations.’³

There were countless such examples – and even Darwin’s discussion of kelp at the coast of Tierra del Fuego as the most essential plant in the food chain was strikingly similar to Humboldt’s description of the Mauritia palms as a keystone species that ‘spreads life’ in the Llanos. The great aquatic forests of kelp, Darwin wrote, supported a vast array of life forms, from tiny hydra-like polyps to molluscs, small fish and crabs – all of which in turn fed cormorants, otters, seals and finally, of course, the indigenous tribes. Humboldt informed Darwin’s understanding of nature as an ecological system. Like the destruction of a tropical forest, Darwin said, the eradication of kelp would cause the loss of uncountable species as well as probably wiping out the native population of Fuegians.

Darwin modelled his own writing on Humboldt’s, fusing scientific writing with poetic description to such an extent that his journal of the Beagle voyage became remarkably similar in style and content to the Personal Narrative. So much so that his sister complained after receiving a first part of his journal in October 1832 ‘that you had, probably from reading so much of Humboldt, got his phraseology’, and ‘the kind of flowery french expressions which he uses’. Others were more complimentary and told Darwin later how delighted they were with his ‘vivid, Humboldt-like pictures’.

Humboldt showed Darwin how to investigate the natural world not from the claustrophobic angle of a geologist or zoologist, but from within and without. Both Humboldt and Darwin had the rare ability to focus in on the smallest detail – from a fleck of lichen to a tiny beetle – and then to pull back and out to examine global and comparative patterns. This flexibility of perspective allowed them both to understand the world in a completely new way. It was telescopic and microscopic, sweepingly panoramic and down to cellular levels, and moving in time from the distant geological past to the future economy of native populations.

In September 1835, a little less than four years after leaving England, the Beagle finally departed from South America to continue circumnavigating of the globe. They sailed from Lima to the Galapagos Islands, which lay 600 miles west off the Ecuadorian coast. These were strange barren islands on which birds and reptiles lived that were so tame and unaccustomed to humans that they could be easily caught. Here Darwin investigated rocks and geological formations, collected finches and mockingbirds and measured the size of the giant tortoises that roamed the islands. But it was only when he eventually returned to England and examined his collections that it became clear how important the Galapagos Islands would become for Darwin’s evolutionary theory. For Darwin the islands marked a turning point, although he didn’t realize it at the time.

After five weeks in the Galapagos, the Beagle sailed on into the emptiness of the South Pacific towards Tahiti, and from there to New Zealand and Australia. From the western coast of Australia they crossed the Indian Ocean and rounded the tip of South Africa before sailing across the Atlantic Ocean back to South America. The last months of the voyage were hard on everybody. ‘There never was a Ship,’ Darwin wrote, ‘so full of home-sick heroes.’ Whenever they met merchant vessels during those weeks, he felt the ‘most dangerous inclination to bolt’ and jump ship, he admitted. They had been away for almost five years – so long, that he found himself dreaming of England’s green and pleasant lands.

On 1 August 1836, after crossing the Indian Ocean and then the Atlantic, they briefly stopped in Bahia in Brazil, where they had made their first South American landfall at the end of February 1832, before finally turning north for the last leg of their voyage. Seeing Bahia was a sobering experience for Darwin. Instead of admiring the tropical blooms in the Brazilian rainforest as he had during their first visit, he now longed to see stately horse chestnuts in an English park. He was desperate to get home. He had had enough of this ‘zig-zag manner’ of sailing, he wrote to his sister. ‘I loathe, I abhor the sea, & all ships which sail on it.’

By the end of September they passed the Azores in the northern Atlantic and sailed towards England. Darwin was in his cabin, as seasick as he had been on his first day. Even after all these years, he was still not used to the rhythm of the sea and moaned, ‘I hate every wave of the ocean.’ Lying in his hammock, he filled his bulging journal with his last observations, summing up his thoughts about the previous five years. First impressions, he noted in one of his very last entries, were often shaped by preconceived ideas. ‘All mine were taken from the vivid descriptions in the Personal Narrative.’

On 2 October 1836, almost five years after leaving England, the Beagle sailed into Falmouth harbour on the south coast of Cornwall. In order to complete his survey, Captain FitzRoy had still to take one more longitudinal measurement in Plymouth, at exactly the same location where he had taken his first. Darwin, though, disembarked in Falmouth. He couldn’t wait to catch the mail coach to Shrewsbury to see his family.

As the carriage rattled north, he stared out of the window, watching the undulating patchwork of fields and hedgerows unfold. The fields seemed much greener than usual, he thought, but when he asked the other passengers to confirm his observation, they looked at him blankly. After more than forty-eight hours in the coach, Darwin arrived late at night in Shrewsbury and quietly slipped into the house because he didn’t want to wake his father and sisters. When he walked into the breakfast room the next morning, they couldn’t believe their eyes. He was back and in one piece – but ‘looking very thin’, his sister said. There was so much to talk about, but Darwin could only stay a few days because he had to go to London to unload his trunks from the Beagle.

Darwin returned to a country that was still ruled by the same king, William IV, but two important Parliamentary Acts had been passed during his long absence. In June 1832, after immense political battles, the controversial Reform Bill had become law – a big first step towards democracy as it gave cities that had grown during the Industrial Revolution seats in the House of Commons for the first time and extended the vote from wealthy landowners to the upper middle classes. Darwin’s family, who supported the bill, had kept Darwin up to date about the wrangling in parliament as best they could through the letters they sent him during the Beagle voyage. The other exciting news was the passage of the Slavery Abolition Act in August 1834, while Darwin had been in Chile. Though the slave trade had already been banned in 1807, this new Act now prohibited slavery in most parts of the British Empire. The Darwin and Wedgwood families, who had long been part of the anti-slavery movement, were delighted as, of course, was Humboldt who had fiercely argued against the enslavement of fellow human beings ever since his Latin America expedition.

Most important for Darwin, though, was news from the scientific world. He had enough material to publish several books and the idea of becoming a clergyman had long since evaporated. His trunks were stuffed with specimens – birds, animals, insects, plants, rocks and giant fossil bones – and his notebooks were tightly filled with observations and ideas. Darwin now wanted to establish himself in the scientific community. In preparation he had already written to his old friend, the botanist John Stevens Henslow, a few months earlier from the remote island of St Helena in the South Atlantic, asking him to ease his entrance into the Geological Society. He was keen to show off his treasures, and British scientists, who had followed the Beagle’s adventures through letters and reports that had been circulated by newspapers, were longing to meet him. ‘The voyage of the Beagle,’ Darwin later wrote, ‘has been by far the most important event in my life and has determined my whole career.’

In London Darwin dashed through town to meetings at the Royal Society, the Geological Society and the Zoological Society, as well as working on his papers. He had the best scientists examining his collections – anatomists and ornithologists as well as those classifying fossils, fish, reptiles and mammals.⁴ One immediate project was to edit his journal for publication. When the Voyage of the Beagle was published in 1839, it made Darwin famous. He wrote about plants, animals and geology but also about the colour of the sky, the sense of light, the stillness of the air and the haze of the atmosphere – like a painter with lively brushstrokes. Like Humboldt, Darwin recorded his emotional responses to nature, as well as providing scientific data and information about indigenous people.

When the first copies came off the printing presses in mid-May 1839, Darwin sent one to Humboldt in Berlin. Not knowing where to direct his correspondence, Darwin asked a friend ‘for I know no more than if I had to write to the King of Prussia & the Emperor of all the Russias’. Nervous about sending the book to his idol, Darwin employed flattery and wrote in his covering letter that it had been Humboldt’s accounts of South America that had made him want to travel. He had copied out long passages from Personal Narrative, Darwin told Humboldt, so that ‘they might ever be present in my mind’.

Darwin needn’t have worried. When Humboldt received his copy, he replied with a long letter, praising it as an ‘excellent and admirable book’. If his own work had inspired a book like the Voyage of the Beagle, then that was his greatest success. ‘You have an excellent future ahead of you,’ he wrote. Here was the most famous scientist of the age, graciously telling the thirty-year-old Darwin that he held the torch of science. Though forty years Darwin’s senior, Humboldt had immediately recognized a kindred spirit.

Humboldt’s letter was not one of shallow compliments – line after line he commented on Darwin’s observations, quoting page numbers, listing examples and discussing arguments. Humboldt had read every page of Darwin’s account. Even better, he also wrote a letter to the Geographical Society in London – which was published in the society’s journal for all to read – stating that Darwin’s book was ‘one of the most remarkable works that, in the course of a long life, I have had the pleasure to see published’. Darwin was ecstatic. ‘Few things in my life have gratified me more,’ he said, ‘even a young author cannot gorge such a mouthful of flattery.’ He was honoured to receive such public praise, Darwin told Humboldt. When Humboldt later instigated a German translation of Voyage of the Beagle, Darwin wrote to a friend, ‘I must with unpardonable vanity boast to you.’

Darwin was in a frenzy. He worked on a wide range of subjects from coral reefs and volcanoes to earthworms. ‘I cannot bear to leave my work even for half a day,’ he admitted to his old teacher and friend, John Stevens Henslow. He worked so much that he had heart palpitations which seemed always to occur, he said, when something ‘flurries me’. One reason might have been an exciting discovery about the bird specimens that they had brought back from the Galapagos Islands. As Darwin analysed his finds, he began to deliberate on the idea that species might evolve – the transmutation of species, as it was then called.

The different finches and mockingbirds that they had collected on the different islands were not, as Darwin had initially thought, just variations of the familiar birds on the mainland. When the British ornithologist John Gould – who identified the birds after the Beagle’s return – declared that they were indeed different species, Darwin worked out that each island had its own endemic species. As the islands themselves were of relatively recent volcanic origin, there were only two possible explanations: either God had created these species specifically for the Galapagos, or in their geographical isolation they had all evolved from a common ancestor that had migrated to the islands.

Darwin’s finches from the Galapagos Islands (Illustration Credit 17.3)

The implications were revolutionary. If God had created plants and animals in the first place, did the concept of evolving species imply that he had made initial mistakes? Similarly, if species became extinct and God continuously made new ones, did this mean that he constantly changed his mind? It was a terrifying thought for many scientists. The discussion about the possible transmutation of species had been rumbling on for a while. Darwin’s grandfather Erasmus had already written about it in his book Zoomania, as had Jean-Baptiste Lamarck, Humboldt’s old acquaintance from the natural history museum in the Jardin des Plantes in Paris.

In the first decade of the nineteenth century Lamarck had declared that, influenced by their environment, organisms might change along a progressive trajectory. In 1830, the year before Darwin set sail on the Beagle, the battle between the ideas of mutable species versus fixed species had turned into a vicious public row at the Académie des Sciences in Paris.⁵ Humboldt had attended the fierce discussions at the Académie during a visit to Paris from Berlin, whispering a running commentary of disparaging remarks about the fixed species arguments to the scientists sitting next to him. Already in Views of Nature, more than two decades previously, Humboldt had written about the ‘gradual transformations of species’.

Darwin was also convinced that the idea of fixed species was wrong. Everything was in flux, or, as Humboldt said, if the earth was changing, if land and sea were moving, if temperatures were cooling or rising – then all organisms ‘must also have been subjected to various alterations’. If the environment influenced the development of organisms, then scientists needed to investigate climates and habitats more closely. Therefore, the focus of Darwin’s new thinking became the distribution of organisms across the globe, which was Humboldt’s specialty – at least for the world of plants. Plant geography, Darwin said, was a ‘key-stone of the laws of creation’.

As Humboldt had compared plant families on different continents and from different climates, he had discovered vegetation zones. He had seen how similar environments often contained closely related plants, even when divided by oceans or mountain ranges. Yet this was confusing too because despite these analogies across continents, a similar climate didn’t always, or even necessarily, produce similar plants or animals.

As Darwin read Personal Narrative, he highlighted many of these examples.⁶ Why was it, Humboldt had asked, that the birds in India were less colourful than those in South America, or why was the tiger only found in Asia? Why were the great crocodiles so plentiful in the Lower Orinoco but absent from the Upper Orinoco? Darwin was fascinated by these examples and often added his own comments in the margins of his copy of Personal Narrative: ‘like Patagonia’, ‘in Paraguay’, ‘like Guanaco’ or sometimes just an affirmative ‘yes’ or ‘!’.

Scientists like Charles Lyell explained that these related plants that were found across huge distances had been produced in several centres of creations. God had made these similar species in tandem at the same time and in different regions, in a series of so-called ‘multiple creations’. Darwin disagreed and began to underpin his ideas with arguments on migration and distribution, using Humboldt’s Personal Narrative as one of his sources. He underlined, commented and devised his own indexes for Humboldt’s books as well as writing reminders to himself on sheets that he glued on to the endpapers – ‘When studying Geograph of Canary Botany look at this part’ – or jotting down in his notebook ‘Study Humboldt’ and ‘consult the VI Vol. of Pers. Narra.’ He also commented, ‘Nothing respect to Species Theory’, when the sixth volume did not yield the necessary examples.

Species migration became a main pillar of Darwin’s evolutionary theory. How did these related species move across the globe? To find an answer Darwin conducted many experiments, for example testing the survival rate of seeds in salt water to investigate the possibility of plants having crossed the ocean. When Humboldt noted that an oak that grew on the slope of Pico del Teide in Tenerife was similar to one in Tibet, Darwin queried ‘how transported was acorn … Pidgeons bring grain to Norfolk – Maize to Artic’. When Darwin read Humboldt’s account of rodents opening the hard-shelled Brazil nuts and how monkeys, parrots, squirrels and macaws fought over the seeds, Darwin scribbled in the margin: ‘so dispersed’.

Where Humboldt was inclined to believe that the conundrum of the movement of plants could not be solved, Darwin took up the challenge. The science of plant and animal geography, Humboldt wrote, was not about ‘the investigation of the origin of beings’. What exactly Darwin thought when he underlined this statement in his copy of Personal Narrative we don’t know, but it was clear that he had set out to do precisely that – he was going to find out about the origin of species.

Darwin began to think about common ancestry, another subject for which Humboldt provided plenty of examples. The crocodiles of the Orinoco were gigantic versions of European lizards, Humboldt said, while ‘the shape of our little house pet is repeated on a larger scale’ in the tiger and jaguar. But why did species change? What triggered their mutability? As one of the main proponents for the transmutation theory, the French scientist Lamarck had argued that the environment had changed, for example, a limb into a wing, but Darwin believed this to be ‘veritable rubbish’.

Darwin found the answer in the concept of natural selection. In autumn 1838 he studied a book that helped him shape these ideas: English economist Thomas Malthus’s Essay on the Principle of Population. Darwin read Malthus’s gloomy prediction that human populations would grow faster than their food supply unless ‘checks’ such as war, starvation and epidemics controlled the numbers. The survival of a species, Malthus had written, was rooted in an overproduction of offspring – something that Humboldt had also described in Personal Narrative when discussing the enormous amount of eggs that turtles laid in order to survive. Seeds, eggs and spawn were produced in huge quantities but only a tiny fraction grew to maturity. There is no doubt that Malthus provided what Darwin called ‘a theory by which to work’, but the seeds of this theory had been sown much earlier when he had read Humboldt’s work.

Humboldt discussed how plants and animals ‘limit each other’s numbers’ as well as noting their ‘long continued contest’ for space and nourishment. It was a relentless battle. The animals that he had encountered in the jungle ‘fear each other’, Humboldt observed, ‘benignity is seldom found in alliance with strength’ – an idea that would become essential to Darwin’s concept of natural selection.

At the Orinoco Humboldt had commented on the population dynamics of capybaras, the world’s largest rodents. As he had paddled along the river, he had observed how rapidly the capybaras reproduced, but also how jaguars chased them on land and how crocodiles devoured them in the water. Without these ‘two powerful enemies’, Humboldt had noted, capybara numbers would have exploded. He had also recorded how jaguars pursued tapirs and that monkeys screamed ‘affrighted at this struggle’.

‘What hourly carnage in the magnificent calm picture of Tropical forests,’ Darwin scribbled in the margins. ‘To show how animals prey on each other,’ he noted, ‘what a “positive” check.’ Here, written in pencil in the margins of Humboldt’s fifth volume of Personal Narrative, Darwin recorded for the first time his ‘theory by which to work’.

In September 1838 Darwin wrote in his notebook that all plants and animals ‘are bound together by a web of complex relations’. This was Humboldt’s web of life – but Darwin would take this a step further and turn it into a tree of life from which all organisms stem, with the branches leading to extinct and to new species. By 1839 Darwin had formulated most of the basic ideas that underpinned his theory of evolution, but he continued to work on it for twenty more years before he published the Origin of Species in November 1859.

Fittingly, even the last paragraph of the Origin of Species was inspired by a similar section in Personal Narrative, highlighted by Darwin in his own copy. Darwin took Humboldt’s evocative description of thickets teeming with birds, insects and other animals⁷ and turned it into his famous entangled bank metaphor:

It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us.

Darwin was standing on Humboldt’s shoulders.

¹ Worried about the little space in the poop cabin, Darwin had asked the captain before the departure if he was allowed to take his own copy of Personal Narrative. ‘You are of course welcome to take your Humboldt,’ the captain assured him.

² The Beagle also carried a missionary and three Fuegians whom FitzRoy had taken hostage on his previous voyage and brought to England. They were now to return home to Tierra del Fuego where FitzRoy hoped that they would convert their fellow Fuegians to Christianity once he had set up a missionary settlement there.

³ The entire description reads very similarly. Humboldt’s ‘the earth is shaken on its old foundations, which we had deemed so stable’, becomes in Darwin’s journal: ‘the world, the very emblem of all that is solid, moves beneath our feet.’ Humboldt wrote, ‘we mistrust for the first time a soil, on which we had so long placed our feet with confidence,’ and Darwin followed with: ‘one second of time conveys to the mind a strange idea of insecurity.’

⁴ Darwin also secured government funding to publish Zoology of the Voyage of H.M.S. Beagle – to ‘resemble on a humbler scale’ Humboldt’s magnificent zoological publications, he said.

⁵ In the corner of the fixed species argument were those who believed that animals and plants became extinct and that God regularly created new ones. Their opponents argued that there was an underlying unity or a blueprint from which different species developed as they adapted to their particular environment – variants of what Goethe had called ‘urform’. They argued that the wings of a bat or the paddle of a porpoise, for example, were all variations of forelimbs.

⁶ There are several hundred references to Humboldt in Darwin’s manuscripts – ranging from Darwin’s pencil marks in Humboldt’s books to notes on Humboldt’s work in Darwin’s notebooks such as ‘In Humboldt great work’ or ‘Humboldt has written on the geography of plants’.

⁷ Humboldt wrote in Personal Narrative: ‘The beasts of the forest retire to the thickets; the birds hide themselves beneath the foliage of the trees, or in the crevices of the rocks. Yet, amid this apparent silence, when we lend an attentive ear to the most feeble sounds transmitted by the air, we hear a dull vibration, a continual murmur, a hum of insects, that fill, if we may use the expression, all the lower strata of the air. Nothing is better fitted to make man feel the extent and power of organic life. Myriads of insects creep upon the soil, and flutter round the plants parched by the ardour of the Sun. A confused noise issues from every bush, from the decayed trunks of trees, from the clefts of the rock, and from the ground undermined by the lizards, millepedes, and cecilias. There are so many voices proclaiming to us, that all nature breathes; and that, under a thousand different forms, life is diffused throughout the cracked and dusty soil, as well as in the bosom of the waters, and in the air that circulates around us.’