More than a century before today's proponents of intelligent design theory began arguing that life is too complex to arise through the natural process of evolution, Charles Darwin, evolution's main man, was causing trouble.
He didn't set out to upset people. He was, after all, a strict creationist himself, on his way toward becoming an Anglican clergyman, when he embarked at age 22 on the odyssey of naturalistic observations that would provide the grist for his revelation. His inscribed Bible was among the few belongings he brought along for his seminal journey aboard the H.M.S. Beagle.
And the young traveler certainly didn't seek to rearrange the intellectual world order of Western society. In fact, he waited until he was 50 to publish his 1859 treatise, On the Origin of Species, and he only did that because he knew a scientific rival, Alfred Russel Wallace, was onto the same idea and was ready to go public. Darwin had been sitting on the controversial notion of evolution and natural selection for 21 years.
"He was worried about social disorder -- he saw the idea as being so powerful and so disruptive it made him ill," says Niles Eldredge, a paleontologist and curator of a new exhibit on Darwin at the American Museum of Natural History in New York. Darwin, he notes, even wrote to his scientist friend Joseph Hooker, describing the publication of his work as akin to "confessing a murder."
The release of Darwin's masterwork marked a singular moment in the history of science. "These works contain the most arresting and significant set of ideas relating to man and to his surroundings that has ever come from the scientific mind," wrote Robert Jastrow, scientist and best-selling author, in his 1984 book The Essential Darwin1.
The theory produced an immediate backlash of criticism from scientists, conservative theologians and others. The aftershocks still are being felt. The recent forays by intelligent design theorists represent only the latest -- though perhaps the most politically savvy -- attacks on the father of evolution.
Darwin's law, which holds that evolution works on plants and animals through differences in their reproductive success, shifted man from the center of creation. All forms of life on the earth have evolved out of other forms that lived at an earlier time, and those in turn had evolved out of other forms, Darwin argued. Humans were just part of the glorious picture.
The revolutionary theories of Copernicus and Galileo had succeeded in moving the Earth from the center of the universe, but they had not undermined the idea of a creation supervised by Divine Providence. Darwin's did.
"Darwin's evolutionary theory is the explanation for why life is so diverse and why there are millions of different species on the surface of the planet," says Michael Novacek, a senior vice president at the natural history museum and one of the discoverers of Mongolia's Ukhaa Tolgod, the richest cretaceous fossil site known in the world. "Darwin said organisms evolve from ancestors by descent and they change through time and they adapt and change to new situations and they diverge from each other."
Darwin returned from his Beagle voyage having observed species so similar yet diverse that they suggested descent with modification from common ancestors. Over the remaining decades of his life (he died in 1882 at age 73), he amassed convincing circumstantial evidence -- from myriad sources that included rock sediment, beetles, barnacles, butterflies, iguanas, tortoises, skeletons and fossils -- that all forms of life on Earth had evolved under similar forces.
Every creature on the planet, he concluded, is a cousin to every other -- even humans. Man, Darwin wrote, "is descended from a hairy, tailed quadruped, probably arboreal in its habits." He shocked the world in saying so and instantly joined the ranks of civilization's greatest minds, like Newton and Einstein, who have contributed to the scientific understanding of humanity's place in the cosmic order.
Building on his observations, Darwin devised a tightly constructed theory of evolution. A population grows until it approaches the limit of its resources, he noted. A struggle for existence then ensues, and those individuals with the traits that help them overcome obstacles, such as climate or predators, are more likely to survive and produce offspring.
Offspring inherit the traits of their parents and carry them on to future generations.
Individuals with traits that handicap them for survival will reproduce less, and their traits will tend to disappear from the population. Over time, the process gradually transforms the species, preserving some traits, pruning away others.
This process, the creative power that generates new forms of life, is "natural selection," according to Darwin. (The phrase "survival of the fittest" was not his but coined by a friend, Herbert Spencer.)
Challenging his faith
When Darwin first came to the idea that species might change, which provided a starting point for his theory of evolution, he did not see it immediately as a challenge to his Christian faith, according to Randal Keynes, Darwin's great-great-grandson and author of Darwin, His Daughter and Human Evolution.
"He hung on as long as he could to his beliefs about the Christian faith and God's role and so on," said Keynes. "Then he thought and thought and thought. His wife, Emma, was a devout Christian. He knew how much her faith meant to her. He thought some more. At the end of the day, he couldn't accept that it made sense that the world was created by a benevolent creator given there was so much pain and disease in the world."
Darwin wanted to believe, Keynes said. But "he couldn't. He didn't know what the answer was. That's why he said he was an agnostic, not an atheist."Many, including Keynes, believe Darwin's ultimate loss of faith stemmed from the death of his 10-year-old daughter Anne, probably from tuberculosis.
Many scientists, however, embrace both evolution and religion. "There is a huge mosaic of personal beliefs on this," says Novacek, the paleontologist.
What Darwin couldn't figure out and left for future generations -- he ran out of time, he said -- was the notion of "directedness." Looking at the history of life over the course of eons, he noted that it seemed to have a flow and direction: lower forms to higher, simple to complex. Whether the forces of evolution are guided by a higher force was something he couldn't answer. Many scientists think such questions are beyond the realm of science.
Despite the conflict between traditional religious views of creation and the theory of evolution, Darwin's research did not diminish his sense of awe at the wonders at work in the world. The last paragraph of his Origin sums up this tension nicely: "There is a grandeur in this view of life," he wrote. "From so simple a beginning, endless forms most beautiful and wonderful have been, and are being, evolved."
The Darwin Digital Library of Evolution, which features the broadest and most complete collection ever assembled of specimens, artifacts, original manuscripts and memorabilia related to Darwin, can be found on the Internet at http://darwinlibrary.amnh.org/.