It is interesting during these intermediate years to watch from time to time the occasional side-hints of Darwin's activity and of the interest it aroused among his scientific contemporaries. In 1854, for example, Sir Charles Lyell notes, after an evening at Darwin's, how Sir Joseph Hooker astonished him with an account of that strange orchid, Catasetum, which bears three totally distinct kinds of flowers on the same plant; 'It will figure,' he says, 'in C. Darwin's book on species, with many other "ugly facts," as Hooker, clinging like me to the orthodox faith, calls these and other abnormal vagaries.' On a similar occasion, a little later, Lyell asks, after meeting 'Huxley, Hooker, and Wollaston at Darwin's,' 'After all, did we not come from an ourang?' Last of all, in 1857, Darwin himself writes an anticipatory letter to his American friend, Asa Gray, in which he mentions 'six points'--the cardinal conceptions of the 'Origin of Species.' His book is now fairly under weigh; he speaks of it himself to acquaintance and correspondents as an acknowledged project.
Events were growing ripe for the birth. A lucky accident precipitated its parturition in the course of the year 1858.
Alfred Russel Wallace, a young Welsh biologist, went out at twenty-four, in 1848, to the Amazons River, in company with Bates (the author of 'The Naturalist on the Amazons'), to collect birds and butterflies, and to study tropical life in the richest region of equatorial America. Like all other higher zoologists of their time, the two young explorers were deeply interested in the profound questions of origin and metamorphosis, and of geographical distribution, and in the letters that passed between them before they started they avowed to one another that the object of their quest was a solution of the pressing biological enigma of creation or evolution. Starting with fresh hopes and a few pounds in pocket, on an old, worn-out, and unseaworthy slave-trader, they often discussed these deep problems of life and nature together upon the Sargasso sea, or among the palms and lianas of the Brazilian woodlands. The air was thick with whiffs and foretastes of evolutionism, and the two budding naturalists of the Amazons expedition had inhaled them eagerly with every breath. They saw among the mimicking organisms of that equatorial zone strange puzzles to engage their deepest attention; they recognised in the veins and spots that diversified the filmy membranes of insects' wings the hieroglyphs of nature, writing as on a tablet for them to decipher the story of the slow modification of species. In 1852--the year when Herbert Spencer in England published his essay on the 'Development Hypothesis,' and when Naudin in France put forth his bold and able paper on the 'Origin of Species'--Wallace once more returned to Europe, and gave to the world his interesting 'Travels on the Amazons and the Rio Negro.' Two years later the indefatigable traveller set out a second time on a voyage of tropical exploration, among the islands of the Malay archipelago, and for eight years he wandered about in Malay huts and remote islets, gathering in solitude and isolation the enormous store of minute facts which he afterwards lavished with so prodigal a hand upon 'Tropical Nature,' and the 'Geographical Distribution of Animals.'