It's well known that Charles Darwin's groundbreaking theory of evolution made many people furious because it contradicted the Biblical view of creation.
But few know that it also created problems for Darwin at home with his deeply religious wife, Emma.
Darwin held back the book to avoid offending his wife, said Ruth Padel, the naturalist's great-great-granddaughter.
"She said he seemed to be putting God further and further off," Padel said in her north London home. "But they talked it through, and she said, 'Don't change any of your ideas for fear of hurting me.'"
The 1859 publication of "On the Origin of Species" changed scientific thought forever — and generated opposition that continues to this day.
It is this elegant explanation of how species evolve through natural selection that makes Darwin's 200th birthday on Feb. 12 such a major event.
More than 300 birthday celebrations are planned in Britain alone, where Darwin's face graces the 10-pound bill along with that of Queen Elizabeth II.
Shrewsbury, the central England town where Darwin was born and raised, is holding a monthlong festival for its most famous son. And a permanent exhibition re-creating some of his most famous experiments is opening at Down House, his former home near London.
Many more events are planned worldwide, including the Second World Summit on evolution in the Galapagos islands in August. In Australia, the Perth Mint is putting out a special commemorative silver coin.
Even Darwin's ideological adversaries concede that he was a towering figure.
"He was clearly extremely important, his thinking changed the world," said Paul Taylor, a spokesman for Answers in Genesis, a prominent group that rejects Darwin's theory of evolution in favor of a literal interpretation of the Bible. "We disagree with his conclusions, with the way he made extrapolations, but he was a very careful observer and we've got a lot to be grateful for."
Bob Bloomfield, special projects director at London's Museum of Natural History, said Darwin was cautious not only because he didn't want to offend his wife, but also because he understood that the concept of man's evolution from other animals was controversial.
He didn't want to present it simply as a hypothesis, but as an explanation buttressed by many observations and facts.
"He knew he had to make an absolutely iron-cast case for his theory," Bloomfield said. "He was one of the earliest true scientists where everything he was prepared to write about had to be based on evidence."
Darwin's small, handwritten diaries are on display at a major exhibit at the Museum of Natural History, as well as thousands of specimens he collected.
Some came from his fabled five-year trip to South America aboard the Beagle, when he visited the remote Galapagos Islands and saw how some species had adapted to its strange, demanding environment.
The diaries offer insights into Darwin's meticulous, analytical approach. He even lists the pros and cons of getting married.
The advantages? A wife would be a constant companion, a friend in old age, and fill the house with music and feminine chitchat.
The cons? Losing the freedom to come and go as he pleased and to read as much as he wanted at night. Visiting relatives. And he would have to spend money on children, not books.
After much deliberation, Darwin renounced the single life: "One cannot live this solitary life, with groggy old age, friendless & cold, & childless staring one in ones face, already beginning to wrinkle," he concluded.
It is in the diaries that Darwin's personality best comes through, said Padel, one of 72 great-great-grandchildren.
"That's where his real life was," said Padel, an acclaimed poet. "He had the most amazing sense of wonder. He was always thinking, 'How does that work?' And that led him to everything."
Once he married, Darwin turned his family into willing research assistants. He enlisted his wife to play piano to a jar of earthworms placed on the piano lid to see if they would respond to music (they didn't).
Stephen Keynes, a great-grandson, said Darwin also enlisted his children to throw flour on bees so the path of their flight could be followed. There are no reports of any of the children being stung.
"He was the most wonderful father, ever," said Keynes, 81. "He allowed his children access to his study where he was working at any time."
Darwin was also an innovator at home. He put wheels on the chair in his study so he could get to his specimens more quickly — and, bingo, the modern office chair was invented.
His passion to understand nature's unseen workings made him a frequent visitor to the London Zoo, where he made friends with an orangutan called Jenny.
He offered Jenny a mouth organ and showed her her reflection in the mirror. He also noted that when her keeper would not give her an apple, she pouted and sulked like a child.
These seemingly trivial observations helped Darwin develop his theory that man evolved from primates.
"He was very interested in the expressions of animals and in particular primates and how similar they could be to humans," said Becky Coe, an education director at the zoo, which is setting up a temporary "Darwin Trail" using animals to help explain evolution.
Coe said Darwin went back to the zoo time and time again to make sure he had physical evidence for every aspect of his theory.
Darwin's inquisitiveness outlasted his physical vigor.
"Late in life when he was quite ill, he would look at plants curling up at the window, bending to the light, and he would wonder, 'How do they do that?'" said Padel. "He was constantly thinking of relationships and that led him to understand natural selection. He realized that every population is in competition with every other. He realized that is how species adapt, because they are always competing for light, water and food."
What would he be doing if he were alive today?
Padel thinks he would probably be studying DNA and the immune system. And she thinks the great scribbler would be online much of the time.
"He'd be a demon at e-mail," she said.