Charles Darwin might have spent his life quoting Genesis rather than studying speciation had it not been for his friendship with a professor of botany at Cambridge, John Stevens Henslow.  Two years into his training for the Holy Orders, Darwin fell under the wing of Professor Henslow.  The two men frequently strolled the campus together, prompting dons to call Darwin “the man who walks with Henslow.”  Darwin later recalled that his mentor’s “strongest taste was to draw conclusions from long-continued minute observations.”  In 1831, when Henslow received a call from Admiralty asking whom he could recommend as a naturalist on a voyage of the H.M.S. Beagle to map the South American coastline, he identified his favorite pupil.  Darwin’s father at first fought the idea, preferring that his playboy, dog-loving, “rat-catching” son stick on the road to the clergy.  Eventually, however, he relented—perhaps persuaded by the argument of Charles’s uncle, Josiah Wedgwood II, that “the pursuit of natural history, though certainly not professional, is very suitable to a clergyman.” (DB, 466-67) 

Over the course of Darwin’s five-year voyage on the Beagle he became a different person.  Writing late in life, Darwin remarked, “Looking backwards, I can now perceive how my love for science gradually preponderated over every other taste.”  (CD, 78)  He came, as he put it, to discover “the pleasure of observing and reasoning.”  (CD,79)  His love of close observation, coupled with a desire to come up with a theory for everything, lay at the heart of his genius.  Previously, the world had seen many great fact-gatherers and many others adept at theorizing, what it had never seen before was a biologist who combined both these skills and who could present to the world a powerful and encompassing vision of the development of life on earth.

Darwin’s theory did not, contrary to popular opinion, suddenly pop into his head as he observed differences in the beaks of Galapagos finches.  His thoughts on the origins of species developed slowly.  For one thing, his understanding of the age of earth made any theory such as natural selection seem impossible.  Prior to a meeting in Cape Town, South Africa with esteemed geologist Sir John Herschel in June 1836, near the end of the Beagle’s voyage, Darwin shared the popular view that Bishop Ussher’s chronology was essentially correct.  “As far as I know everyone has yet thought that six thousand odd years has been about the right period,” he wrote in a letter to his sister, “but Sir J. thinks that a far greater number must have passed”—and clearly Darwin soon thought Herschel had it right.

The great notion of how selection—for centuries understood in the context of engineering plants and livestock—might apply in the wild came two years after Darwin’s return to England.  He recalled later that inspiration stuck in October 1838 when he was reading “for amusement ‘Malthus on Population.’”  Writing of the event, he said: “It at once struck me that under these circumstances favorable variations would tend to be preserved and unfavorable one to be destroyed.  The result of this would be the formation of new species.”  (DBD, 469)  Malthus’s work demonstrated how, unchecked, populations could soar to astronomical levels over just a few generations.  Darwin grasped how, in nature, disease, predation, and weather events conspire—over the long run—to favor those variations of a species that provided even modest defenses against the grim reaper. As Darwin observed, even a “trifling difference” can “which shall survive and which perish.”  Those with the right chance adaptations survive to breed and pass along their new trait, while those that lack the adaptation perish without offspring. (Hux, 245) Over the next several years, the great naturalist expanded his ideas on speciation through natural selection into a 230-page abstract.  Then, remarkably, he let his revolutionary work gather dust for fourteen years while he raised a family and tended to other scientific studies.  (BB, 383-85)

A letter from a young naturalist in 1858 finally spurred Darwin to publish his theory.  The letter came from a friend of his, Alfred Russell Wallace.  Wallace laid out a draft of his own ideas on the subject of the origin of species.  Darwin quickly that Wallace’s ideas bore a striking resemblance to his own.  “If Wallace had my manuscript sketch,” Darwin wrote, “he could not have made a better short abstract.”  (BB, 386)

Darwin found Wallace’s letter strangely bothersome.  Ideas that he developed only through years of careful and plodding work came to his young friend in a single insightful flash.  It hardly seemed fair.  Nonetheless, Darwin recognized Wallace’s contribution.

On July 1, 1858, Darwin buried his retarded eighteen month-old son, who succumbed to scarlet fever.  That same day, the theory of evolution was announced to the world—or, more accurately, thirty or so persons at a meeting of the Linnaean Society.  The paper bore the names of both Darwin and Wallace.  Wallace, for his part, generously referred to the theory forever afterwards as “Darwinism.”

The sketches and essays of Darwin and Wallace, which filled seventeen pages of the Linnaean Society’s 1858 journal, in the words of Darwin, “excited very little attention.”  He recalled later that the only published response provoked by the papers came from a Dublin professor “whose verdict was that all that was new in them was false, and what was true was old.” (DB, 469-470) At the end of the year, Thomas Bell, the president of the Society, noted, “The year which has not, indeed, been marked by any of those striking discoveries which at once revolutionize…the department of science on which they bear.”  (DB, 464-65)

Darwin fretted whether his editor, John Murray, might find his ideas too unorthodox to be published.  He asked a scientist-friend whether he should point out that he did not “bring in any discussion about Genesis…and only give facts” or whether it would be wiser to “say nothing to Murray” in the hopes that he will not fully grasp how revolutionary his work truly was.  He needn’t have worried; Murray decided to publish after reading only the chapter titles.  (DB, 474-75)

Darwin’s work on evolution, called Origin of Species, was published in London in November 1859.  His editor, skeptical of the level of interest in such a theory, encouraged him to write next time about another interest of Darwin’s: pigeons.  “Everyone is interested in pigeons,” he assured him.  Despite his editor’s reservations, the first printing of 1,250 copies sold out on the first day, and the book has remained in print ever since.  (BB, 380-81)

Nowhere in the first edition of Origin of Species does the word “evolution” appear.  Instead, Darwin refers to his theory as “descent with modification.”  Only in the sixth edition did Darwin, finally giving into widespread use of the term, substitute the term “evolution” for the phrase he favored.  (BB, 384)

Critics soon began pointing to alleged problems with Darwin’s explanation for the emergence of new species.  First, they argued that the earth was far too young to allow for the gradual evolution of species as Darwin proposed.  By this time, thanks to the work of Buffon and others, scientists unanimously rejected Ussher’s estimate of a 6,000 year-old-earth.  Nonetheless, they generally agreed that the earth must be only tens of millions of years old, not billions.  Lord Kelvin, a respected applied mathematician of the day, had calculated that in about 24 million years a body the size of the sun would consume all its available fuel—and, it scarcely needed to be pointed out—the earth could not be older than the sun.  A second difficulty with Darwin’s theory seemed to be the scarce fossil support.  Scientists wondered why, if Darwin was right, there were not hundreds of (“transitional”) fossils representing “missing links” between species.  (BB, 389-90)

Another criticism of his theory, however, gave Darwin more difficulty.  Critics saw little chance that complicated organs such as the eye could have emerged gradually.  They must, it was believed, be the work of an intelligent designer.  Darwin seemed to admit to having doubts himself.  He wrote, “It seems, I freely confess, absurd to the highest possible degree” that natural selection could produce such organs gradually.  (BB, 390)  Nevertheless, Darwin believed the theory could account for such things, given enough time.  In Origin of Species, he speculated how an organ such as the eye might have developed, writing that "any sensitive nerve may be rendered sensitive to light" and that step could begin a process, "though insuperable to our imagination" that could lead to formation of "a perfect and complex eye...through natural selection." (Decades later, evolutionary biologists would take up the challenge of  tracing the evolution of the eye.  They would point out, for example, that the human eye shares many “quirky vestiges of extinct ancestors, such as a retina that appears to have been installed backwards.”)  (SP,51)

Eventually, most scientists—if not laypersons—would see flaws in Kelvin’s calculations and transitional fossils would begin to appear.  (Conveniently, one such fossil was discovered in 1861, just two years after publication of Origin of Species.  It was an archaeopteryx, a creature that sharing features of both dinosaurs (teeth) and birds (feathers).) (BB, 389)  Moreover, there gradually arose an appreciation of how difficult in was to become a fossil.  Over 99.9% of all living things end up as decayed matter, and even the .1% that don’t are unlikely to be fossilized and then discovered.

Over time, the theory propounded by Darwin and Wallace became increasingly viewed as Darwin’s alone.  Wallace’s interests veered off towards socialism, women’s rights, extra-terrestrials, and communication with the dead. (BB, 387-88)  Most significantly, Wallace began to back off from the implications of his own theory.   He concluded that the mind could not be a product of evolution, and could only be the design of a superior intelligence.  He rejected the idea that man was subject to “the blind control of a deterministic world.”  (SP, 28)  Darwin expressed some misgivings about Wallace’s new spiritualism.  In a letter to his old friend he wrote, “I hope you have not murdered too completely your and my own child.”  (DB, 472)

In Origin of Species, Darwin kept his focus on explaining how new species emerged over time.  He carefully avoided any discussion of the origin of humans.  In 1871, however, Darwin made the connections between apes and humans explicit when he published his second great work on evolution, The Descent of Man.  Darwin argued that his theory could account for the emergence of a species capable of self-conscious thought.  The human brain evolved from the brains of extinct species, he concluded.  The mind, despite all of the mysteries it held, was just the accidental outcome of random variations over time.  Man’s “wonderful advancement,” according to Darwin, “largely depended” on the evolution of “articulate language,” not on any special programming added by a watchful creator.  (R&L, 42)

To his critics, these ideas robbed man of his special place in the universe.  The implications were profoundly troubling.  Darwin made man the consequence of a series of improbable events.  Our chances of being on this planet, his theory suggested, were remote in the extreme. Replay the universe a billion times, and in none of those replays would humans likely have emerged.  A single break anywhere on the long chain that led to us—and there have been several periods of mass extinctions—and there would have been no human history.

In his last years, Darwin felt freed by evolving social attitudes toward religion to reveal an agnosticism that he had long kept hidden.  Writing in 1879, he observed, “Nothing is more remarkable than the spread of skepticism or rationalism during the latter half of my life.”  (CD,95)  Reflecting on his years aboard the Beagle, Darwin described his religious views at the time as “quite orthodox.”  (CD,85)  He wrote, in an autobiography edited by his son Frank, “I remember being heartily laughed at by several of the officers (though themselves orthodox) for quoting the Bible as an unanswerable authority on some point of morality.”  During the two years after his return to England, however, Darwin’s views on religion evolved.  He came to see “that the Old Testament from its manifestly false history of the world, with the Tower of Babel, the rainbow as a sign, etc., etc., and from its attributing to God the feelings of a revengeful tyrant, was no more to be trusted that the sacred books of the Hindus, or the beliefs of any barbarian.” (CD, 85)  His loss of orthodoxy seemed to him a consequence of his greater understanding of science: “The more we know of the fixed laws of nature, the more incredible do miracles become.” (CD, 86) Despite growing doubts about “Christianity as a divine revelation,” Darwin moved to agnosticism gradually and reluctantly.  “Thus disbelief crept over me at a very slow rate,” he wrote in his autobiography, “but at last it was complete.  The rate was so slow that I felt no distress, and have never since doubted even for a single second that my conclusion was correct.” (CD, 86-87)

A famous argument for the existence of God left Darwin utterly unconvinced.  In 1802, William Paley presented the “watchmaker” argument in the opening passage of Natural Theology: "In crossing a heath, suppose I pitched my foot against a stone, and were asked how the stone came to be there; I might possibly answer, that, for anything I knew to the contrary, it had lain there forever: nor would it perhaps be very easy to show the absurdity of this answer. But suppose I had found a watch upon the ground, and it should be inquired how the watch happened to be in that place; I should hardly think of the answer I had before given, that for anything I knew, the watch might have always been there."   Paley’s “common sense’ conclusion—there must have been a watchmaker—leads him to the obvious analogy: the marvelous designs of nature must have been the work of a Creator.  As he argued in his popular book, "Every indication of contrivance, every manifestation of design, which existed in the watch, exists in the works of nature; with the difference, on the side of nature, of being greater or more, and that in a degree which exceeds all computation."

Darwin wrote that Paley’s argument, which  “formerly seemed to me so conclusive,” fails “now that the law of natural selection has been discovered.  We can no longer argue,” Darwin continued, “that, for instance, a beautiful hinge of a bivalve shell must have been made by an intelligent being, like the hinge of a door by man.”  Darwin said natural selection persuaded him that “there is no more design in the variability of organic beings and in the action of natural selection, than in the course which the wind blows.  Everything in nature is the result of fixed laws.” (CD, 87)

There is a hint in Darwin’s autobiography that he recognizes that a natural world governed solely by fixed laws loses some of its magic.  He quoted how, in the journal he wrote while on the Beagle’s voyage, he had described the grandeur of a Brazilian rainforest: “It is not possible to give an adequate idea of the higher feelings of wonder, admiration, and devotion which fill and elevate the mind.” (CD, 91)  Darwin remembered being filled with “conviction that there is more in man than the mere breath of his body.”  His understanding of natural selection and the passing years emptied this feeling.  “But now,” he lamented, “the grandest scenes would not cause any such convictions and feelings to rise in the my mind.  It may truly be said that I am like a man who has become color-blind, and the universal belief by men of the existence of redness makes my present loss of perception of not the least value as evidence.”  (CD, 91)

Darwin’s theory, by implication, suggested that evolution might also explain morality.  Indeed, he saw in animals the types of empathy that underlie moral systems.  (R&L, 41) A belief in God, he speculated, is “perhaps an inherited effect on [children’s] brains” and that it “would be as difficult for them to throw off their belief in God as for a monkey to throw off its instinctive fear and hatred of the snake.”  (CD, 93)  When Charles Darwin’s son, Frank, edited his father’s autobiography in 1885, the quoted portion of preceding line was one that prompted a concerned letter from Darwin’s wife, Emma Darwin, who had reviewed Frank’s compilation.  She called it “the one sentence in the Autobiography which I very much wish to omit.”  In part, she acknowledged, she objected to it because “your father’s opinion that all morality has grown up by evolution is painful to me.”  She complained that the sentence “gives one a sort of shock” and worried how readers might react to the equating of spiritual beliefs and “the fear of monkeys toward snakes.”  (CD, 93n2)  The sentence that so shocked his wife, is also, it turns out, one that goes to the heart of a controversy that remains heated to this day: Is there something in our epistemological make-up that makes us ask the God Question?

Charles Darwin understood better than anyone how his theory on the origin of new species threatened prevailing religious beliefs.  He referred to himself as “the Devil’s Chaplain” and complained that publishing the theory felt “like confessing a murder.”  He knew especially well how his ideas troubled his pious wife.  (BB, 388)

Darwin’s view left no place for God--or so it seemed to those who would take up the fight against evolution.  Morality, his religious critics would maintain, had to have a transcendent source or all was lost.  (SP, 52)  Not only would Darwin’s naturalizing of the mind attract the fire of Fundamentalists, but also many other religious leaders who accepted other aspects of his theory.  For example, the Pope in 1996 acknowledged that evolution was “more than just an hypothesis,” but he insisted that evolution could not account for “the spiritual soul.”  The spirit, he stated, could not develop “from forces of living matter.”  Any theory that contends otherwise is not compatible “with the dignity of the person.”  (SP, 186-87)

Shortly before Darwin died in 1882 and was buried in Westminster Abbey (next to Isaac Newton), he was visited by a young American studying in England, Henry Fairfield Osborn.  Osborn would become, by the time of the Scopes trial, the nation’s leading paleontologist and expert on evolutionary biology.  John Scopes traveled to see Osborn at the American Museum of History in New York when he visited the city to meet with ACLU officials coordinating his trial work.  Osborn told Scopes of his earlier meeting with Darwin and said, “I was greatly inspired.  Now you young men can see me, and I hope you’ll be equally inspired!”  (GMT, 94)  Osborn told Scopes that his wife’s illness would prevent him from traveling to Dayton for the trial, but he promised to secure a letter of support from Leonard Darwin, the great naturalist’s son and president of the Eugenics Education Society.  

Osborn was true to his word, and Leonard Darwin sent his note of encouragement to John Scopes.  Darwin congratulated Scopes on his “courageous effort to maintain the right to teach well established scientific theories.”  Darwin told Scopes, “To state that which is true can not be irreligious.”  He ended the letter with the words, “May the son of Charles Darwin send you in his own name one word of warm encouragement.”  (GMT, 94-95)