The Invention of Nature

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.