Seringueiros [rubber tappers] were, by default, the true settlers of Brazil's interior. When Henry Ford had introduced the Model T in 1908, the Amazon had been the world's sole source of rubber. The wild popularity of these automobiles, and the seemingly insatiable demand for rubber that accompanied them, had ignited a frenzy in South America that rivaled the California gold rush. In The Sea and the Jungle, H. M. Tomlinson complained that the only thing Brazilians saw in their rich rain forests in 1910 was rubber. "It is blasphemous that in such a potentially opulent land the juice of one of its wild trees should be dwelt upon ... as though it were the sole act of Providence," he wrote. "The passengers on the river boats are rubber men, and the cargoes are rubber. All the talk is of rubber." Two years before Roosevelt had set sail for South America, his friend the great American naturalist John Muir had been similarly astonished by the rubber lust that he had witnessed as he traveled through the Amazon. "Into this rubbery wilderness thousands of men, young and old, rush for fortunes," he marveled, "half crazy, half merry, daring fevers, debilitating heat, and dangers of every sort."SOURCE: The River of Doubt: Theodore Roosevelt's Darkest Journey, by Candice Millard (Doubleday, 2005), pp. 317-318
By the time Roosevelt reached the Amazon, the dangers were still there but the promise of riches had all but disappeared. The bottom had dropped out of the South American rubber boom in 1912, when the Amazon lost its lock on the market. Thirty-six years earlier, an Englishman named Henry Wickham had smuggled Hevea brasiliensis seeds, the most popular species of Amazonian rubber tree, out of Brazil. Those seeds had then been cultivated at Kew Gardens, and the British had eventually planted their predecessors in tropical Malaysia. There, far from their natural enemies, the trees could be planted in neat rows with no fear that a blight would destroy the entire crop, as it likely would have done in South America. Labor in Malaysia was also not only cheap but readily available, and much more easily controlled. So successful had been the transfer of rubber trees to the Far East that by 1913 Malaya and Ceylon were producing as much rubber as the Amazon.