Editor's Note: This post is also appearing at the American Institute for Biological Sciences' Year of Science 2009: Celebrate Evolution. For more on Darwin's 200th birthday, see our January 2009 issue on evolution.

"If I were to give an award for the single best idea anyone ever had, I'd give it to Darwin." So wrote philosopher Daniel Dennett in his 1995 book Darwin's Dangerous Idea. "In a single stroke, the idea of evolution by natural selection unifies the realm of life, meaning and purpose with the realm of space and time, cause and effect, mechanism and physical law."

Dennett's musing really hits home to anyone who took introductory biology that did not include evolution: such a course is a giant survey of the different kinds of plants, animals and other organisms of our planet, tied together by a single principle--you needed to know it for the final. But evolution by natural selection ties all life together with process and chemistry. As the great biologist Theodosius Dobzhansky famously, and correctly, said, "Nothing in biology makes sense except in the light of evolution."

The idea itself is fairly easy to grasp (which may be one reason why people who would never dream of finding fault with Einstein feel qualified to dispute Darwin): in populations of organisms, each individual is a bit different from every other; the differences may give that individual a bit of a survival advantage; that individual is more likely to pass on the traits that helped it survive; that trait becomes more widespread; rinse; repeat. In a few hundred million years, you can go from amoebae to elephants (and still have amoebae).

Of course, in the decades since the publication of Origin of Species, scientists have learned much more about the evolutionary process than Darwin could have dreamed of. Genes get duplicated; chromosomes get rearranged; viruses shuttle genetic information from one species directly to another; individual genes govern the activity of other genes. But Darwin got much of the overall picture right--a remarkable achievement for a man working with whole organisms, before the unraveling of heredity on the molecular level of DNA.

A line from early in the Origin, published in 1859, reveals how he did it. "On my return home, it occurred to me, in 1837, that something might perhaps be made out on this question [of the origin of species] by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it." In other words, collect a lot of data and then think about it long and hard. Imagine what the world might be like if, say, politicians or financial analysts adopted that philosophy.

The incorporation of genetics into evolutionary theory in the first half of the 20th century led to what is called "the modern synthesis." Julian Huxley, grandson of Darwin's friend and defender Thomas Henry Huxley, discussed DNA in relation to evolution in 1963. After a brief review of the structural characteristics of DNA, Huxley writes, "The various properties of DNA which I have mentioned make evolution inevitable. The existence of an elaborate self-reproducing code of genetical information ensures continuity and specificity; the intrinsic capacity for mutation provides variability; the capacity for self-reproduction ensures potentially geometric increase and therefore a struggle for existence; the existence of genetic variability ensures differential survival of variants and therefore natural selection; and this results in evolutionary transformation." Voila.

You'll be hearing a lot about Darwin in 2009. In addition to it being the 150th anniversary of the debut of the Origin, February 12th of this year is the bicentennial of his birth. (Were he one of the tortoises he studied on the Galapagos Islands, he might even still be here to celebrate it--a tortoise probably collected by Darwin himself lived until 2006.) So happy 200th, Charles Darwin! There is indeed "grandeur in this view of life," a view he bequeathed to all of us.

Photo of Steve Mirsky coming out of his shell at the Bronx Zoo by Molly Frances