It was a theory that took 20 years to evolve.
 
Today, Charles Darwin’s name is synonymous with evolution, but he waited two decades before publishing his ideas about natural selection, partly because of the inevitable backlash. “It went against what people had been taught for centuries,” explains Sean B. Carroll, a biology professor and author of The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution.
 
After completing his voyage on the HMS Beagle in 1836, Darwin spent the next several years in a period of “mental rioting,” continually jotting down his thoughts to work out whether his radical theory was correct.
 
Once Darwin convinced himself of the theory’s legitimacy, his still had to wrestle with significant resistance both personally and professionally.
 
The conflicts came in large part from those closest to him. His wife, Emma, was devoutly religious, and “she worried about their life together in eternity,” says Carroll. Darwin also needed to consider the senior scientists who had made his original journey – and scientific career – possible. “His theory would be like spitting in their face.”

In 1859, when Darwin finally published On the Origin of Species, the debate was indeed heated – and personal. Many newspapers published scathing reactions and less-than-flattering cartoons of Darwin as a monkey.
 
However, the time that Darwin took to construct his theory paid off. “Darwin actually referred to the book as ‘one long argument,’” says Carroll. “I think a lawyer would admire 'The Origin of Species' because Darwin – in that book – examines evidence for and against his ideas.”
 
Even the original title “On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life” shows how carefully Darwin laid out his arguments. In the face of this thorough – and time-consuming – research, his critics could only raise weak objections.
 
After its 20-year incubation, Darwin’s theory began to divide religious leaders, politicians, and the public – divisions that continue to this day.