Humboldt’s most consequential findings, however, derived from his conception of the world as a single unified organism. “Everything,” he said, “is interaction and reciprocal.” It seems commonplace today to speak of “the web of life,” but the concept was Humboldt’s invention. Into the seventeenth and eighteenth centuries, thinkers like René Descartes, Francis Bacon, and Carl Linnaeus were still echoing Aristotle’s view that “nature has made all things specifically for the sake of man.”
Particularly heterodox was the implication that the decline of one species might have cascading effects on others. The possibility that animal life might not be inexhaustible had been proposed by the German anatomist J.F. Blumenbach (who taught Humboldt at the University of Göttingen), but was not widely accepted. “Such is the œconomy of nature, that no instance can be produced of her having permitted any one race of her animals to become extinct,” declared Thomas Jefferson in 1784, an opinion shared by most naturalists. Convinced to the end of his life that mastodons still existed in North America, most likely in the “unexplored and undisturbed” regions of the continent, Jefferson urged Lewis and Clark to look for them during their expedition.
Humboldt traveled so far, saw so much, and observed so closely that he began to notice similarities across continents. Rhododendron-like plants on the mountains near Caracas reminded him of alpine trees in the Swiss Alps; a sea of cacti, seen from the distance, recalled the grasses in the marshes of northern Europe; a moss in the Andes resembled a species he had found growing in German forests.
This comparative approach allowed him to take staggering intellectual leaps. He looked beyond the characteristics of organisms and tried to determine the structures underlying nature, leading him to formulate the idea of ecosystems. He was the first to understand that climate emerged from the “perpetual interrelationship” between land, ocean, wind, elevation, and organic life. He introduced the idea of classifying plants by climate zones instead of taxonomy, taking into account altitude, temperature, and other conditions related to location. He invented isotherms, the lines used on maps to connect regions with the same average temperature and atmospheric pressure. The similarity of the coastal plants in Africa and South America led him to postulate an “ancient” connection between the continents, anticipating plate tectonic theory by more than a century. He also studied how different systems interacted with one another. Nobody before Humboldt, for instance, had been able to explain how forests, by releasing oxygen, storing water, and providing shade, have a cooling effect on climate.
In the Llanos, the vast grasslands that stretch from the Andes to the Amazon River, Humboldt noticed with wonder how many species found food or protection from the occasional Mauritia palm tree. It sheltered insects and worms from the wind, provided fruit to monkeys and birds, retained moisture and soil, and generally spread “life around it in the desert.” The Mauritia palm was what, two centuries later, would come to be known as a “keystone species,” an organism on which the health of an entire ecosystem depends.
If everything in nature interacted, then it stood to reason that the natural world was not stable but prone to dynamic changes. It followed that man, by disrupting the natural order, might inadvertently bring about catastrophe. Humboldt was among the first to write of the perils of deforestation, irrigation, and cash crop agriculture, asserting that the brutal repercussions of man’s “insatiable avarice” were already “incalculable.” During his yearlong expedition to Russia in 1829, he gave a speech at the Imperial Academy of Sciences in St. Petersburg calling for a vast international collaboration in which scientists around the world would collect data related to the effects of deforestation, the first global study of man’s impact on climate, and a model for the Intergovernmental Panel on Climate Change, assembled 160 years later.
The idea that human beings might be interfering with the natural order of things was a radical rejection of prevailing views about man’s dominion over nature. These views were most forcefully expressed by the French naturalist Georges-Louis Leclerc, comte de Buffon, who wrote with disgust of primeval nature; his Natural History is replete with words like “grotesque,” “filth,” “nauseous,” “pestilential,” and “terrible.” Buffon’s views echoed those of William Bradford, the first governor of the Plymouth Colony, who described the new world as “a hideous and desolate wilderness, full of wild beasts and wild men,” and the English naturalist John Ray, who wrote of man’s duty to bring nature in line with God’s design through settlement and cultivation. To Humboldt, however, man was “nothing” in the larger scheme of things. Wulf notes that nowhere in his five-volume magnum opus, Cosmos—his attempt to summarize his thinking on the natural world, the universe, and the entirety of human history—does Humboldt mention God.
By casting aside religious and political ideology, Humboldt was able to diagnose plainly the cruelties of colonial rule. The sight of the slave markets in the Spanish colonies made him a fervent abolitionist. He told Americans (though not Jefferson himself) that slavery was a “disgrace” and that the oppression of Native Americans was a “stain” on the nation. Humboldt was the first to make the correlation between colonialism, with its crude emphasis on extracting resources and disregard for indigenous populations, and ecological devastation.
Humboldt wrote figuratively, with high emotion, of the beauty he found in wilderness. Wulf calls his rhapsodic Views of Nature “a blueprint for much of nature writing today.” Just as his scientific views influenced Darwin and Marsh (who warned in Man and Nature that “climatic excess” might lead to the “extinction of the [human] species”), Humboldt’s lyricism served as a model for Thoreau, Haeckel, and Muir. Wulf dedicates a chapter to each of these figures, all of whom idolized Humboldt and drew liberally from his work.
Darwin stands out as the most slavish of his acolytes, writing in his journal that Humboldt “like another Sun illumines everything I behold.” Darwin wrote that it was Humboldt’s Personal Narrative, a seven-volume subsection of Voyage, that inspired him “to travel in distant countries, and led me to volunteer as naturalist in her Majesty’s ship Beagle.” He brought his copy of the Personal Narrative on the Beagle with him and read in it Humboldt’s discussion of the “gradual transformations of species.” Humboldt wrote that plants and animals “limit each other’s numbers” through “long continued contest” for nourishment and territory, with only the strongest surviving—an idea, Wulf notes with some understatement, “That would become essential to Darwin’s concept of natural selection.” Wulf also points out that the final, crowning paragraph of Origin of Species is a nearly verbatim plagiarism of a passage in Personal Narrative.