Two hundred years ago Thursday, two of the most influential men of all time were born on the same day -- one in a three-story country mansion in Shrewsbury, in Shropshire, England, and the other in a one-room, dirt-floor frontier log cabin in Kentucky.
Many believe English biologist Charles Darwin and American statesman Abraham Lincoln did more to change the world than any other figures in 19th Century history. Historians credit the pair with guiding the world into modernity.
Darwin did it by piecing together the theory of evolution, which, from the time it first appeared in his 1859 book "On the Origin of the Species," so thoroughly blew apart conventional scientific, religious and social thought and theory that 150 years later the dust still hasn't settled.
When Lincoln became president in 1861, much of the world still regarded the American ideal of democracy as a shaky, unstable experiment on the verge of failing.
"Lincoln lived and validated the American dream," said biographer Harold Holzer, who is co-chairman of the United States Lincoln Bicentennial Commission. "He saved the American experiment in its severest test, and validated the nation's founding documents by ridding us of slavery."
Though the men started out in the world in vastly different circumstances on the day they were born, an astonishing number of common threads weave through their lives.
Each shared an underlying gloominess of the soul, perhaps related to losing their mothers at an early age. Darwin's mother died when he was 8 years old; Lincoln's died when he was 9. Lincoln suffered bouts of deep, near-suicidal depression for the rest of his life. Darwin suffered from crippling anxiety.
As boys, each was a voracious reader, immersing themselves to distraction, which did not serve them well with cold and distant fathers who thought their sons were lazy daydreamers who would not amount to much.
At age 22, Lincoln struck out on his own to try to make a life in New Salem, Ill. His illiterate father, who used to yank Abe out of school to hire him out to neighbors, expressed to a family friend his doubt about his son's new life:
"I suppose that Abe is still fooling hisself with eddication. I tried to stop it, but he has got that fool idea in his head, and it can't be got out."
When Darwin left home -- at age 22 -- and joined the five-year scientific survey expedition aboard HMS Beagle, his father tried to stop it, thinking it was a further waste of his son's time. "You care for nothing but shooting, dogs, and rat catching," he told his son as a teenager, "and you will be a disgrace to yourself and your family."
As fathers, Darwin and Lincoln each resolved to be loving parents involved in their children's lives and, for Lincoln's part, spoiled them to the point of scandal. As president he let his young sons openly dash into and interrupt meetings in the White House any time they pleased.
Each man was devastated at the death of their favorite children. With Darwin, it was his daughter, Annie, who had shown an intellect to match his own by the time she died of tuberculosis at age 10. Lincoln's pet son, Willie, who shared his father's passion for reading and poetry, died of typhoid at 11.
Those deaths had telling but different impacts on the religious beliefs of both men, who had long been skeptical of the traditional Christian beliefs they were born into. Most everybody in 1809 was satisfied with the Bible's creationist teachings that the world was roughly 5,000 years old and that every kind of animal and plant was unchanged from the way God originally created them.
As the 19th Century progressed, however, the new science of geology suggested Earth is far older than the Bible said, stirring up troubling questions about the Bible's literal truth and triggering doubts in many, including Lincoln and Darwin.
In fact, Lincoln was attacked for being a heathen when he ran for Congress in 1846, a charge so serious that he had to publish the only public statement he ever made about his personal religious views:
"That I am not a member of any Christian Church, is true; but I have never denied the truth of the Scriptures: and I have never spoke with intentional disrespect of religion in general, or of any denomination of Christians in particular."
Lincoln largely ignored organized church religion and dogma as an adult. But Willie's death so devastated him, his wife Mary said, that it seemed to turn him back to religion and the Bible, which he read regularly and deeply.
Darwin, whose own religious belief dissolved as he worked out the principles of evolution, withheld publishing the theory for 20 years because of his fear of religious backlash.
He knew churchmen and devout believers everywhere would excoriate him for suggesting the Bible was wrong, possibly hurting his beloved family in the bargain. He also bent to the will of his wife Emma, an extremely devout Christian who was terrified he would be damned for his views and they would not be together in eternity.