In July 1799, the 29-year-old Prussian naturalist and explorer Alexander von Humboldt finally reached South America. When he docked in New Andalusia (present-day Venezuela), he plunged his thermometer into the sand, logging a temperature of 37.7ºC. It would be the first of the many thousands of recordings he would make during his journey across the Americas, from testing the charge of electric eels on his own arm to measuring earthquake tremors in Caracas and taking periodic altitude readings on his precious barometers that smashed one by one as the voyage progressed. 

Accompanied by his close companion the French naturalist Aimé Bonpland, Humboldt travelled light, setting off into the interior across the baking Llanos grasslands. The men crammed leaves into their hats to protect themselves from the heat. They collected a menagerie of eight monkeys, seven parrots, a toucan and a macaw along the way, and as they entered the rainforests they found a world teeming with life, in which ‘man is nothing’. Ascending the Upper Orinoco, Humboldt mapped its fabled connection with the Rio Negro – a tributary of the Amazon – via the Casiquiare canal.

Humboldt’s travels in South America would climax near the summit of Chimborazo – a towering volcano in the Andes, a hundred miles to the south of Quito. It was here that his intuitions of the deep interconnectedness of nature found their expression. His climb took him through the world’s climatic zones, layered one on top of the other, from the tropical vegetation of the valleys, through temperate oaks and ferns on the slopes into the alpine environment of pines, lichen and mushrooms. The experience was captured in Humboldt’s iconic Naturgemälde – a three-foot by two-foot sketch of Chimborazo in profile, charting the distribution of climatic and natural features at each altitude, indicating the height of Mont Blanc, Vesuvius, Cotopaxi and Gay-Lussac’s balloon ascents for comparison. ‘Instead of placing plants in their taxonomic categories,’ writes Andrea Wulf, ‘he saw vegetation through the lens of climate and location: a radically new idea that still shapes our understanding of ecosystems today.’

Humboldt’s sketch summed up his views of nature as an intricately interwoven whole. ‘Long bands’ of similar vegetation circled the globe, dispersing similar types of shrubs, grasses and pines in similar climatic zones. The drawing’s visual immediacy and aesthetic appeal also reflected his deeply held view that art and science were two sides of the same coin; for him, subjective aesthetic emotion worked hand in hand with the objective truth. It was a posture that made him a pioneer of literary scientific writing.

On his return to Europe, Humboldt became one of the most famous scientists of his age. An intellectual omnivore, he spent his days conversing with colleagues, absorbing new ideas, experimenting, dealing with a prodigious quantity of correspondence (he would write 50,000 letters over the course of his life and received thousands each year) and writing multi-volume works on his travels. In the evenings he moved from salon to salon, talking non-stop to a captivated audience. He was, Wulf writes, ‘the hub of a spinning wheel, forever moving and connecting’, in constant motion ‘like a planet moving along its orbital path’. He craved new explorations but was frustrated by political circumstance until his late, epic expedition across Russia, which he undertook at the age of fifty-nine.

Wulf also hints at a more subdued inner life that could barely express itself in the times he lived. He was brought up in an intellectually rich but emotionally repressive environment and was, in his own words, ‘forced into a thousand constraints’. Despite being the centre of high-society attention across Europe and the object of many eligible women’s fancies, he never married. ‘I don’t know sensual needs,’ Humboldt admitted, but he nevertheless formed very close relationships with his male colleagues and travel companions, including Bonpland. The result was intense social interactions but limited intimacy. In the end, ‘loneliness had been his most loyal companion throughout his life’.

A child of the Enlightenment, Humboldt lived into the Romantic era and what gave his science vitality was his embrace of both reason and emotion. For Humboldt science did not rob nature of its mystery and beauty. Rather it intensified it, and as a result of this holistic vision his influence spread across the intellectual firmament. While the Romantic poets – Wordsworth, Coleridge and Southey – were drawn to Humboldt’s literary descriptions of his travels, Darwin used his ideas and proto-evolutionist scientific intuitions, and Goethe was equally fascinated by his multi-dimensional approach.

Politically, he lived to see the rupture of the French Revolution, Napoleon’s rise and fall and the subsequent monarchist revival, as well as the independence movements across the Americas. Zelig-like, he met and influenced all the main players, from Thomas Jefferson to Simón Bolívar. He admired the ethos of the emerging polity of the United States, but deplored slavery; he supported progressive movements across Europe, but was forced through financial necessity to spend much of his life as a chamberlain to the Prussian court.

The contradictions did not stop there. Humboldt was of noble birth, but a combination of mismanaged finances, boundless scientific ambition and generosity to others meant that he struggled financially and ended in penury. Late in life he was still living in a small, rented second-floor apartment, unable to afford a complete edition of his own books. His room was jammed with manuscripts, maps, folios, stuffed animals, rock specimens and even a pet chameleon. Still mentally sharp, he had begun his physical decline with failing hearing and diminishing stamina.

Andrea Wulf’s The Invention of Nature is a dazzling account of Humboldt’s restless search for scientific, emotional and aesthetic satisfaction. Unapologetically in awe of her subject and intent on restoring Humboldt’s reputation, she brings his ideas to the foreground – their emergence, spread and evolution after his death. The physical Humboldt disappears about two-thirds of the way through the book, with his death in 1859 soon after the publication of the final volume of his grand synthesis, Cosmos: A Sketch of the Physical Description of the Universe. The last third of the book looks at how his ideas lived on and developed in the minds of a series of other naturalists, writers and early environmentalists. There are chapters on Darwin, Henry David Thoreau, George Perkins Marsh, Ernst Haeckel and John Muir, all of whom drew heavily on his ideas. Wulf goes as far as to say that modern environmentalists, ecologists and nature writers are still drawing from his oeuvre, even if they have never heard of him.

If science has moved from a great joining up of observations, ideas and theories to a systematic pulling apart of subject areas into narrower and narrower specialisations, then Humboldt’s intellectual life stands as the supreme example of the first approach. With the environmental movement, ecology and climate science, Wulf argues, we may have entered another period in which connections predominate over isolated proofs, bringing renewed relevance to Humboldt’s grand visions of nature, the world and the universe.