Charles Darwin was born 200 years ago today, and has been dead for almost 127 years. That's a long time in human terms, but no time at all in the history of life on earth. Though the true age of our planet (about 4.6 billion years) wasn't yet clear in his time, Darwin knew that it was very old—old enough to have changed a whole lot, and for life to have evolved along with it.
If he hadn't, someone else would have figured out around Darwin's time that evolution happens by natural selection. The evidence, from geology, paleontology, island ecology, animal breeding, and other fields was there. Indeed, someone else did figure it out, and when Alfred Wallace wrote to Darwin about "the Tendency of Varieties to Depart Indefinitely From the Original Type" in 1857, he spurred Darwin to spend two years compiling his own ideas on the subject (by then 20 years old), in On the Origin of Species, 150 years ago this year.
But while the idea of natural selection was ripe for discovery in the mid-1850s, Charles Darwin was uniquely suited to refine and present it. He was a polymath, interested in a huge variety of subjects. He was a well-respected member of the British social and scientific establishment, so his ideas would be heard. He had traveled the world, observing and collecting different species of animals and plants, before returning to England to become a settled homebody, set on performing exacting experiments to tease out the subtleties of biological phenomena.
Long before he wrote the Origin, he understood the implications of his discovery, especially to Biblical interpretations of creation—he had trained for the ministry in his youth, and his wife Emma was very religious—so he knew that he would have to assemble all the overwhelming evidence he had, and argue it well, to make his case. That's one reason he waited 20 years.
Despite knowing nothing of genetics, plate tectonics, or modern developmental biology, and having few transitional fossil finds to refer to, Darwin and Wallace were fundamentally correct in their discovery:
So while many people assume that On the Origin of Species addresses how life originated on earth to start with, it doesn't—that remains a mystery biologists are still trying to solve 150 years later. Darwin himself suggested that life was "originally breathed by the Creator into a few forms or into one."
His book solved another mystery altogether: how new species originate from existing ones. In doing so, Charles Darwin effectively created the science of biology, drawing the study of living things into a cohesive subject, where insights in one field (such as the chemical structure of deoxyribonucleic acid inside cells) could relate to others (like the geographic distribution of animals, or even human medicine).
Darwin was a shy, sensitive family man averse to controversy, but he was also stubborn, logical, meticulous, and a completist. The Origin is over 300 pages, but he wrote it as a mere abstract of the comprehensive book he really wanted to write (and never did). Even in its "abbreviated" form, it is a progressing, relentless treatise, building fact upon fact.
He doesn't introduce the concept of natural selection until the fourth chapter (of 15 total). He builds a foundation, introduces his discovery, marshals evidence, raises objections, and addresses them. He talks about instinct, breeding, geology, geography, morphology, and embryology. Then, just to be sure you've got it, he writes a final chapter summarizing everything—all in long Victorian paragraphs.
Honestly, On the Origin of Species is a pretty dull read. But it is a stupendous argument.
The test of a scientific theory is not only what it explains, but what it predicts—even beyond what its formulators might have imagined. We know Newton's laws of motion are right because we use them to send men to the moon and probes to planets, and to predict eclipses. We know Einstein was right because lasers actually work, and because gravity really does bend light, whether as close by as the sun or as far away as the most distant galaxies. We know continental drift is real for a bunch of reasons, but today we can even use precise satellite measurements to watch it happening in real time.
Countless theories are obsolete because their predictions don't pan out: a young and earth-centred universe under an unchanging dome of stars, four elements (earth, air, fire, water), aether and phlogiston, Lamarckian inheritance, magical alchemy (Isaac Newton was convinced about that one), spontaneous generation, health as a balance of humours, absolute time, the indivisible atom, Darwin's own ideas about the mechanisms of inheritance, and on and on.
We refine other theories based on new evidence, because their predictions are close, but not quite right. Today, for newer theories, we build huge machines just to find out whose predictions match with reality.
What amazes us about Darwin, and Newton, and Einstein (and others)—what shows us that they were right—is that new evidence keeps turning up, and either refines or confirms what their most important theories predict, but doesn't refute it. Newton's theories work so well we hardly think about them: we just buy cameras with refracting lenses, fly in planes with jet engines, drive cars with airbags, or turn on our GPS units, and we expect them to work. Einstein showed some extreme situations where Newton's laws don't properly apply, and we learned from that how to make laser pointers, take radiation therapy, and fear nuclear weapons.
Evolution by natural selection, as Darwin and Wallace figured it out, suggested that we would find many other things, such as:
From biochemistry and molecular biology to evolutionary developmental biology (evo-devo), gene therapy, and evolutionary psychology, whole fields of study depend on the principles of natural selection. Without them, those fields could not make their own predictions or solve problems in the real world.
Yet here's the thing: they do.
That's why today, Darwin day, is worth commemorating. Charles Darwin figured out the basis for how life works 150 years ago. He explained it, and no matter how controversial it remains, natural selection is the basis for how we understand the family of all organisms, extinct or living, which includes ourselves, over several billion years.
He was a proper Victorian country gentleman, so I doubt anyone ever called him "Chuck." But he's 127 years dead now, so he has no reason to mind my saying this: Happy birthday, Chuck. And thanks.