It is this insight – that mistakes are mistakes – that underlies our brain theory. It’s a trivial idea that we all know to be true – set off on the wrong road and you are unlikely to arrive, even if (perhaps especially if) you take every subsequent turning perfectly.

Okay, we said this was going to be easy, and already we are throwing mathematics at you, and trying to convince you that inaccuracy matters in life. So let’s look at the facts: how accurately is DNA copied? As the above account demands, it is copied with an error rate less than 0.0000000001! Biologists know exactly how this prodigious feat is achieved (a "proofreading" process plays a vital role), and they understand that the key events in the origin of life were dramatic increases in this accuracy.

Going back to the brain, we think that incredible accuracy in the adjustment of synapses during learning is what allows the brain to slowly come to understand the world. One way to think about this is to realize that evolution itself is a learning process: populations of organisms learn to survive and reproduce, not in individual lifetimes, but over many generations, by the process of Darwinian adaptation. (It’s because of the connection between Darwinian evolution and synaptic learning that we call our theory Synaptic Darwinism.) Most of our work has focused on proving this idea: that sets of synapses can only learn to understand (or, more neutrally, "model" or "represent") the world if the learning process is phenomenally accurate.

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