Wallace’s turn toward spiritualism hastened an eclipse that had begun when Darwin published “On the Origin of Species.” DAVID HUGHES

When he was twenty-four years old, Alfred Russel Wallace, the greatest field biologist of the nineteenth century, had his head examined by a phrenologist who determined that, while his “organ of wonder” was very big, his “organ of veneration,” representing respect for authority, was noticeably small. Wallace was so struck with the accuracy of this report that, sixty years later, he mentioned it in his autobiography. It was wonder that drew him to nature, and an instinctive disregard for authority that made it easy to challenge an entire civilization’s religious convictions, as he did when, in 1858, he dashed off a paper proposing a theory of evolution by means of natural selection. Unlike Charles Darwin, who spent twenty years keeping a similar conclusion to himself in private dread, Wallace didn’t give a damn what people thought. This utter independence from public opinion is one of several reasons that he has all but vanished from popular consciousness.

Another is simple bad luck. Wallace grew up poor and was always an outsider in the gentlemen’s club that constituted the scientific world of his day. When, in his youth, he sailed to the Amazon to seek his scientific fortune, his ship caught fire and sank on the way home, taking with it thousands of specimens, a number of live monkeys, and his dream of an easy life. Wallace never found steady work and was instead forced to make a living by his pen—risky for a scientist with a restless imagination in a cautious age—supplementing his income by working as a lowly test examiner. Most unluckily of all, Wallace, having completed his explosive paper on evolution, chose to send it to Darwin himself, who then kicked into high gear and brought out “On the Origin of Species” the following year.

Still another reason for Wallace’s obscurity has something to do with that phrenologist. Wallace cracked one of the greatest scientific mysteries of all time but continued to believe throughout his long life that a stranger had read the riddle of his character by feeling the bumps on his head. Phrenology was one of several commitments—like his campaign against vaccination and his credulous defense of spiritualist mediums—that did not endear him to the scientific establishment, or to posterity.

But there are signs that Wallace’s time has finally come. Since 2000, at least five biographies have been published: “The Forgotten Naturalist,” by John Wilson; “Alfred Russel Wallace: A Life,” by Peter Raby; “In Darwin’s Shadow,” by Michael Shermer; “The Heretic in Darwin’s Court,” by Ross A. Slotten; and “An Elusive Victorian,” by Martin Fichman. In addition, two recent anthologies of Wallace’s own writing—“Infinite Tropics: An Alfred Russel Wallace Anthology,” edited by Andrew Berry and introduced by Stephen Jay Gould; and “The Alfred Russel Wallace Reader,” edited by Jane R. Camerini and introduced by David Quammen—give a sample of his consummate writing style. Joseph Conrad kept Wallace’s classic “The Malay Archipelago” on his night table, drawing on it in several of his own books, most notably “Lord Jim.”

G. K. Chesterton once remarked that Wallace was one of the world’s great men because he led a revolution and then a counter-revolution. Having done as much as anyone to overturn traditional religious assumptions, Wallace proceeded to horrify his fellow-evolutionists by concluding that natural selection could not in itself explain the uniqueness of man. He never renounced his evolutionary theory, but instead made it the cornerstone of a theistic explanation of the universe. No wonder a later scientific generation, newly professionalized, ignored him in favor of his more austere and single-minded colleagues. But the twin impulses in Wallace’s work make him compelling and oddly contemporary. He combines both halves of the debate over the meaning of evolution, coolly articulating the materialist mechanisms by which the simplest organisms morphed into human beings while arguing that our existence offers evidence of divine agency. If his name is relatively unknown, his spirit is still making itself felt nearly a hundred and fifty years after his seminal discovery.

Alfred Russel Wallace was born in Usk, Wales, in 1823, to a once prosperous family that had fallen on hard times. His father was a lawyer who never practiced, and who dabbled in doomed literary ventures and made a series of increasingly disastrous investments. Rural Wales remained an important touchstone for Wallace, who encountered there both natural beauty and the poverty of struggling farmers. His education was spotty, but his father read Shakespeare aloud, along with the Bible, Defoe’s “A Journal of the Plague Year,” and the travel writings of Mungo Park; by his early teens, Wallace had himself read “Paradise Lost,” Dante’s “Inferno,” and, perhaps prophetically, “Don Quixote.”

This reading was his primary patrimony. By the time Wallace was thirteen, the family fortunes had sunk so low that his parents could no longer afford to educate him. He was sent to London to board with a brother who was an apprentice carpenter. At the London Mechanics’ Institute, one of several centers of higher learning for the working class, he heard lectures on Robert Owen, the Welsh social reformer, which turned him against the British class system, just as the pamphlets of Thomas Paine, and his brother’s radical views, began turning him against the Church. He was soon packed off again, this time to live with another brother in the countryside north of London, working as an apprentice surveyor, but he took his radical notions with him.

Surveying allowed Wallace to spend his days outdoors, and a new phase of his life began. He discovered geology and botany, purchasing, in 1841, a pamphlet on the structure of plants published by the Society for the Diffusion of Useful Knowledge. Soon, his interest spread to beetles. There are three hundred and fifty thousand described species of coleoptera in the world, more than any other order in the animal kingdom; when a later British biologist, J. B. S. Haldane, was pressed by a clergyman on the nature of God, he reportedly said, “He has an inordinate fondness for beetles.” British naturalists were certainly fond of them, since they could be found all over England. In a public library, Wallace met a young man named Henry Walter Bates, later to become one of the great Victorian entomologists, who was as passionate about natural history as he was. Before long, the young men were planning a tropical adventure in the manner of Alexander von Humboldt and Darwin, whose “Voyage of the Beagle” had been published in 1839, and had fired a generation of restless young naturalists.

Wallace gave himself a crash course in flora and fauna, making local collecting trips and haunting the British Museum. He also read everything on natural history that he could find, including Robert Chambers’s hugely influential book “Vestiges of the Natural History of Creation.” This notorious work, published anonymously in 1844, blended science and creationism and argued passionately for “transmutation”—the notion that present life had evolved from previous forms. This was not a new argument—Darwin’s grandfather Erasmus had suggested as much two generations earlier; the missing key, which both Darwin and Wallace would supply, was the way that evolution worked. But “Vestiges” helped lay the foundation both for popular acceptance of the concept of evolution and for its ultimate scientific articulation. Though rife with unsubstantiated speculation that put off many established men of science (including Darwin, who also took note of how much calumny could be heaped on a man who ventured unpopular, and unproven, scientific opinions), the book excited Wallace and gave his first trip to the Tropics a purpose beyond the chance to flee a dead-end job and follow in the glamorous footsteps of other scientist-adventurers. Although to the outside world Wallace would remain, for some time, a bug collector for hire, without proper affiliations, his theoretical ambitions were present from the outset. He wrote to Bates, “I should like to take some one family to study thoroughly, principally with a view to the theory of the origin of species.”