Evolution By Means of Natural Selection
Of course it has to be Darwin. Nothing else comes close. Evolution by means of natural selection (or indeed any kind of selection—natural or unnatural) provides the most beautiful, elegant explanation in all of science. This simple three-step algorithm explains, with one simple idea, why we live in a universe full of design. It explains not only why we are here, but why trees, kittens, Urdu, the Bank of England, Chelsea football team and the iPhone are here.
You might wonder why, if this explanation is so simple and powerful, no one thought of it before Darwin and Wallace did, and why even today so many people fail to grasp it. The reason, I think, is that at its heart there seems to be a tautology. It seems as though you are saying nothing when you say that 'things that survive survive' or 'successful ideas are successful'. To turn these tautologies into power you need to add the context of a limited world in which not everything survives and competition is rife, and also realise that this is an ever-changing world in which the rules of the competition keep shifting.
In that context being successful is fleeting, and now the three-step algorithm can turn tautology into deep and elegant explanation. Copy the survivors many times with slight variations and let them loose in this ever-shifting world, and only those suited to the new conditions will carry on. The world fills with creatures, ideas, institutions, languages, stories, software and machines that have all been designed by the stress of this competition.
This beautiful idea is hard to grasp and I have known many university students who have been taught evolution at school, thought they understood it, but have never really done so. One of the joys of teaching for me was to see that astonished look on a student's face when they suddenly got it. That was heart-warming indeed. But I also call it heart-warming because, unlike some religious folk, when I look out of my window past my computer to the bridge over the river and the trees and cows in the distance, I delight in the simple and elegant competitive process that brought them all into being, and at my own tiny place within it all.