It is conceivable that, were it possible to scan the brain of pre-Achaean humans – say, in the eighth century BC – one might find some small, but possibly measurable, differences in the structure, or more probably in the functioning, of the brain, compared with the brains of those who lived 1,000 years earlier, or with the modern human brain. But such changes could take place only over very long time scales. As to what is actually happening in the brain when the more recent ‘swings’, those of the last five hundred years or so, take place, nothing is visible (at least nothing on a scale that we
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