JEFFREY BROWN: Today almost 150 years after the origin of species first appeared, evolution theory is again in the news and stirring passions. Charles Darwin appears on magazine covers, a scientific superstar if an embattled one.
But a fascinating new exhibition at New York's American Museum of Natural History looks at the man himself and his own intellectual evolution and shows him as in some ways an unlikely revolutionary who so feared the consequences of his own discoveries he kept them secret for decades.
Niles Eldredge -- an evolution theorist himself -- is the curator of the exhibition and author of the companion book.
NILES ELDREDGE: I think it is almost an unparalleled opportunity to understand the essence of creativity in somebody. It wasn't just on a high; it was a long process of letting nature soak in, so to speak, and then have it sort of bubble up slowly into his conscious brain when he came up with the idea of evolution.
JEFFREY BROWN: Charles Darwin was born into 19th century British privilege, raised largely by his sisters after his mother died when he was eight. His one passion as a youth was collecting beetles. Beyond that, he showed little direction and his father despaired.
NILES ELDREDGE: He was worried that the kid wasn't showing any sort of focus. He said you care about nothing but shooting dogs and rat catching, and you shall be a disgrace to yourself and your entire family.
JEFFREY BROWN: Oh, that's very low expectations for this young fellow.
NILES ELDREDGE: So his dad says okay, so let's put you off to Cambridge, take an undergraduate degree there and become a clergyman so you have some respectable thing to do and you can collect all the beetles you want while you are being a country curie.
JEFFREY BROWN: Hard to imagine now Charles Darwin, the country clergyman. Instead while studying Botany at Cambridge he received an invitation that would change his life and much else -- to be an unpaid naturalist on HMS Beagle, with a mission to explore and collect specimens along the coast of South America.
NILES ELDREDGE: When he got this invitation, of course he jumped at it.
JEFFREY BROWN: Darwin took his bible with him, but the trip he later wrote "determined my whole career." The would-be clergyman became a committed naturalist.
In Argentina, he found bones of giant extinct mammals and noticed similarities to the smaller armadillos he was eating.
NILES ELDREDGE: He didn't say aha, evolution there. But what he said we have extinct ones here, and they are replaced by modern ones. They are a little bit smaller, a little bit different looking. And what would cause that replacement? By the end of the trip he was beginning to ask those kinds of questions.
JEFFREY BROWN: The Galapagos Islands off the coast of Ecuador became his most famous laboratory and the exhibition features island sounds, live tortoises, orange frogs and an iguana.
JEFFREY BROWN: He wrote that he noticed that each Galapagos Island was inhabited by what he called a different set of beings.
NILES ELDREDGE: That's right. He said: If this kind of pattern of slightly different forms of each species are present on each of the islands, it will show us basically that species are not immutable; it is his first writings about the possibility that this differentiation on different islands might lead to truly new species to evolution.
JEFFREY BROWN: To the idea that things change over time.
NILES ELDREDGE: Yes, exactly.
JEFFREY BROWN: Back home Darwin studied his specimens including mocking birds and all kinds of plants. He took copious notes and made this drawing called the tree of life.
At the London Zoo, he watched an orangutan named Jenny and compared it with the behavior of his two young children. Most important, he worked out a mechanism for how evolution works called "natural selection."
NILES ELDREDGE: He had this tremendous insight that just those organisms that were best suited to surviving, making a living, warding off disease and predation, those on the average would be the ones that would reproduce themselves and they would pass on, in a sense, their genetic formula for success on to the next generation, so that was the "aha" -- the one "aha" he really had.
JEFFREY BROWN: But remarkably, Darwin sat on his great "aha" for some 20 years. He lived quietly -- the exhibition has reassembled his study -- in his country house called Down Home. There he pondered the implications of his discoveries. And he had good reason.
His wife Emma, for example, worried that his theory meant the two would never meet in the afterlife. Tragedy further shook Darwin's world and religious beliefs when his ten-year-old daughter Annie died. Eldredge believes Darwin kept silent and suffered physically because he well knew and feared the revolutionary implications of his ideas.
JEFFREY BROWN: He knew what this meant.
NILES ELDREDGE: He really did. Darwin was very concerned that the uproar would be tremendous -- the reaction, negative reaction -- because it was as if he could almost destroy the fabric of British society with this idea. And it really, really troubled him, scared him to death. I think that is the reason why he was ill almost every day of his life. Basically it was an emotional condition that he had because he was keeping a secret.
JEFFREY BROWN: In a famous letter Darwin tells a friend that revealing his theory is like confessing a murder. It would take a letter from a competing scientist, Alfred Russell Wallace, who had worked out a similar theory, to push Darwin to publish.
NILES ELDREDGE: It just freaked Darwin out because Darwin had sat on that idea for 21, 22 years.
JEFFREY BROWN: The "Origin of Species" appeared in 1859, and the rest as this exhibition shows is history. As Darwin's theory was used, sometimes abused, and expanded on down to our own time.
TOUR GUIDE: Seven million years ago we had a common ancestor --
JEFFREY BROWN: The 200th birthday of the man himself comes in 2009 when his legacy, no doubt, will continue to be both celebrated and debated.
JEFFREY BROWN: The Darwin exhibition will travel to museums in Boston, Chicago and Toronto before reaching London to mark the Darwin bicentennial.