He stayed his pen for two decades, fearing the torrent of ridicule his discoveries might unleash. He was so unsure of marriage that he composed a list of pros and cons.

He was a recluse and a slacker and an occasional eater of beetles, and by writing a great revolutionary book this retiring English gentleman changed our fundamental understanding of the natural world, not to mention how Homo sapiens evolved from his apelike grandparents.

Naturalist Charles Darwin is the subject of a masterly new show at the American Museum of Natural History, a testament to the human power of observation and intellectual courage and scientific epiphany. The show, which runs until May 29, 2006, is the broadest and most complete exhibition on Darwin, the man and his ideas. From museums and collections around the globe, the curators have assembled Darwin's manuscripts and magnifying glasses and a painstaking re-creation of his study in the rural town of Down, outside London.

There's a live Galapagos tortoise, many dead beetles and a large and somnolent green iguana.

But it's the reticent man, dead 123 years now, who rivets our attention and accounts for the hint of anxiety that runs through this show. One need only open a newspaper, or wander into a school board meeting anywhere in the United States, to realize the extent to which Darwin's insights -- that we descend from common ancestors and that natural selection drives the evolution of living things -- still roil the culture. By upending the millenniums-old belief that man was created whole by God, Darwin offered an implicit challenge to religious fundamentalists of many creeds.

Who really can be surprised by the persistence and vitality of the cultural resistance?

"Intelligent design," which holds that science can discern the hand of a supernatural force in the machinery of life, is the latest alternative theory to edge onto the public stage. It has attracted a small band of scientists and philosophers, and they are skilled debaters and publicists.

Such challenges are nothing new, extending back centuries. And while this exhibition makes clear that the evidence for evolution is overwhelming, it also reflects the gnawing worry within the scientific class that it has failed to vigorously present its case in the public arena.

"We have a conservative religious element in the United States that is opposed to the notion that we are connected to the rest of the natural world, especially apes," notes Niles Eldredge, a paleontologist and curator of the Darwin exhibit.

Ellen Futter, president of the museum, appends an exclamation mark. "Science is under assault in this country," she said. "The real culprit is the appalling low state of scientific literacy in this country."

Perhaps, although Darwin's education also offers a splendid counterpoint to our Type A, meritocratically obsessed, test-the-kiddies-from-the-womb-until-they-make-crew-at-Harvard culture. Darwin was no prodigy. He cared little for Latin verses, moaning that he could barely remember an e pluribus for 48 hours. His father packed him off at age 16 to Edinburgh University, but Darwin as often arrived at his best lessons wandering through bogs and reading beneath trees.

"You care for nothing," Darwin's father scolded the young wastrel, "but shooting, dogs and rat catching, and you will be a disgrace to yourself and your family."

Young Charlie wasn't inclined to argue. "I have been in such a perfect and absolute state of idleness," he wrote, "that it is enough to paralyze all one's faculties."

The boy was lucky enough to have professors who enjoyed his untamed intellect and helped him to hone a systematic analysis of the natural world. In 1831, he signed on for a five-year tour as a naturalist aboard the HMS Beagle.

Here the exhibition is brilliant, conveying through Darwin's own manuscripts, lithographs, paintings and collections of fossils the flowering of an extraordinary intellect. Darwin was no natural sailor -- seasickness was a steady companion. But nothing bored him. He studied rock upthrusts in Chile to understand how earthquakes caused them. He paddled around the Cocos Islands off Malaysia to develop a theory on the formation of coral reefs.

But evolution was his grand puzzle. Darwin sailed as a deist and an aspiring clergyman but found only challenges and questions in nature. If God created each species singular and static, how to explain the ostrich in Africa and the remarkably similar rhea in South America? God perhaps crafted penguins for the icy outcroppings of Patagonia and Tierra del Fuego, but what to make of their tropical cousins in the Galapagos, who extend winged arms the better to shade paddled feet and ward off sunburn?

"Such facts," he wrote in his red notebook, "undermine the stability of Species." A year later he sketched out his first primitive evolutionary tree, adding the words: "I think."

He returned aflame but not altogether confident. He married his cousin Emma Wedgwood, but only after totting up risks (wives and children are expensive and so time-consuming!) and benefits ("Object to be beloved and played with -- better than a dog anyhow").

All the while he was secretly writing essays on natural selection. The prospect of unveiling those essays summoned a paralyzing fear, as these would challenge religion and science. He told a colleague that even talking of it was "like confessing a murder."

Only in 1858, 22 years after returning from the Beagle, did he summon the nerve to present his theory to the Linnaean Society in London, followed the next year by his book "The Origin of Species." Twelve more years passed and he published "The Descent of Man," which extended his argument to the idea that man, too, had evolved.

Darwin heard more applause than not from the scientific community, but his popular triumph remains in doubt. Even today, against all scientific fact, more Americans believe that the Earth is 6,000 years old and that the biblical flood of Noah shaped the modern world than subscribe to evolutionary theory and intelligent design put together.

And Darwin's theories gave birth to some misshapen children, from early-20th-century eugenicists intent on selecting out "the feeble and the inferior" through sterilization to the German scientist Ernst Haeckel, who found in Darwin's work support for anti-Semitic and racist notions. The exhibition elides this past. Perhaps that's as it should be, as Darwin harbored no such beliefs.

But in its eagerness to declare the grand evolutionary questions settled, the show takes its lone stumble.

Only four decades ago, most paleontologists rejected the theory, now broadly accepted, that comets and volcanic eruptions delivered mass extinctions and so played a key role in speeding evolution. Nor are scientists clear on the mechanism by which one species evolves into another; curator Eldredge and the late scientist Stephen Jay Gould crafted the once heretical theory of punctuated equilibrium, which holds that species sometimes evolve in grand leaps.

And the well-known Cambridge scientist Simon Conway Morris has taken to arguing that even very distant species share structural similarities and journey toward inevitable complexity. This suggests to him that evolution adheres to an architecture.

Which, after a nervous fashion, loops back to the God question.

Ask Eldredge about this and he shrugs. He has a practical scientist's appreciation for Charles Darwin and a theory that, in its broad outlines, grows only stronger. But he harbors no expectation that Americans soon will accept it as writ.

"The issue of who we are and where we came from is far more important to people than whether the Earth revolves around the sun," he says. "These are the elemental questions."

The New York exhibition includes a live Galapagos tortoise and the skeletons of many species.

Scenes from an exhibition, clockwise from above: A five-foot-long iguana; a faithful re-creation of Darwin's study in the rural town of Down, outside London; a skeleton poised under a magnifying glass in the study; a notebook containing Darwin's "tree of life" sketch with the words "I think"; and the naturalist himself. The exhibition runs through May 29, 2006.