Charles Darwin had a big idea, arguably the biggest and best idea ever. And like all the best ideas it is beguilingly simple. In fact, it is so staggeringly elementary, so blindingly obvious, so amazingly ‘dud-duh why didn’t I think of that?’, that although others before him had had inklings of the truth, nobody thought to look for it in the right place. Darwin had 5 years to look for it; and he did so as the official naturalist onboard HMS Beagle - a sailing vessel that spent 5 years travelling the globe from Brazil to Tierra del Fuego - and from the Galapagos to the Malay Archipelago. When he arrived back in England Darwin sat on his idea for 20 years before finally telling the world about it. Why? Because he was scared. He knew it would change everything.
Darwin’s big idea is that of evolution by natural selection published in On the Origin of Species, that gave biology its guiding principle, a governing law that helps the rest make sense. Understanding its cold, beautiful logic is a must. If you want to understand life this is the place to start.
Natural selection's explanatory power is not just about life on this planet: it is the only theory so far suggested that could explain life on any planet. If life exists anywhere else in the universe then some version of evolution by natural selection will almost certainly turn out to underpin its existence. Darwin's theory works equally well no matter how strange and weird and wonderful that extraterrestrial life may be - and my tentative guess is that it will be weird beyond our wildest imaginings.
But what makes natural selection so special? A powerful idea assumes little to explain much. It does lots of explanatory 'heavy lifting', while expending little in the way of assumptions or postulations. It gives you plenty of bangs for your explanatory buck. Its Explanation Ratio - what it explains, divided by what it needs to assume in order to do the explaining - is enormous.
If any reader knows of any idea that has a larger explanation ratio than Darwin's, then I wanna hear it. Darwin's big idea explains all of life and its consequences, and that means everything that possesses more than minimal complexity – that includes you, and me, and the cat next door. It explains flowers and the bees that buzz about them. It explains mushrooms and HIV and athletes-foot-fungus. It even explains accountants. Now that’s what I call explaining! All this explaining is equal to the numerator of the explanation ratio, and it is huge.
Yet the denominator (the number at the bottom of the fraction) in the explanatory equation is spectacularly small and simple. The denominator is: natural selection, the non-random survival of genes in gene pools (to put it in neo-Darwinian terms rather than Darwin's own).
You can winnow Darwin's big idea down to a single sentence (again, this is a modern way of putting it, not quite Darwin's): 'Given sufficient time, the non-random survival of hereditary entities will generate complexity, diversity, beauty, and an illusion of design so persuasive that it is almost impossible to distinguish from deliberate intelligent design'. We don't need to add mutation to our assumptions. Mutational 'bucks' are provided free. 'Given sufficient time' is not a problem either - except for human minds struggling to take on board the terrifying magnitude of geological time. Look around you, the illusion of design is everywhere in the living world. So powerful is this illusion, so soft and comfortable and beguiling is the cotton wool over our eyes, that the spell of the illusion was only recently lifted 150 years ago today. Yes, 2009 is the 150th anniversary of Darwin's big idea - And our eyes are still accustomising to the brilliant new view.
It is mainly its power to simulate the illusion of design that makes Darwin's big idea seem threatening to a certain kind of mind. The same power constitutes the most formidable barrier to understanding it. People are naturally incredulous that anything so simple could explain so much. To a naive observer of the wondrous complexity of life, it just must have been intelligently designed.
But intelligent design is the polar opposite of a powerful theory: its explanation ratio is pathetically titchy. The numerator is the same as Darwin's: everything we know about life and its prodigious complexity. But the denominator, far from Darwin's slim and minimalist simplicity, is at least as big as the numerator itself: an unexplained intelligence, a ‘designer’ big enough to be capable of designing all the complexity we are trying to explain in the first place!
I'll end on a subtler legacy of Darwin's big idea. Darwin raises our consciousness to the sinewy power of science to explain the large and complex in terms of the small and simple. In biology we were fooled for centuries into thinking that extravagant complexity in nature needs an extravagantly complex explanation. Darwin triumphantly dispelled that delusion.
There remain deep questions in physics and cosmology that await their Darwin. Why are the laws of physics the way they are? Why are there laws at all? Why is there a universe at all? Why is there anything? Once again, the lure of 'design' is tempting. But we have the cautionary tale of Darwin before us. We've been through all that before. Darwin emboldens us - difficult as it is - to seek genuine explanations: explanations that explain more than they postulate. Darwin’s big idea is with us for good. There’s nothing quite like it to tear that wool from our eyes!
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