practise of micro-history for example - the way you could construct pictures of forgotten communities or individual lives from state, parish or court records proved breath-taking.

Lots of copying means that many minds get their chance at the problem; imitation ‘makes the contents of brains available to everyone’, writes the developmental psychologist Michael Tomasello in the Cultural Origins of Human Cognition (1999). Tomasello, who is co-director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, calls the combination of imitation and innovation the ‘cultural ratchet’. It is like a mechanical ratchet that permits motion in only one direction – such as winding a watch, or walking through a turnstile. Good ideas push the ratchet forward one notch. Faithful imitation keeps the ratchet from slipping backward, protecting ideas from being forgotten or lost and keeping knowledge alive for the next round of improvement.

In the 1930s, a pair of psychologists raised an infant chimp alongside their own baby in an attempt to understand both species better. The chimp raised in this family (and others in other such experiments later in the century) never behaved much like a human. The human child, on the other hand, soon began knuckle-walking, biting, grunting and hooting – just like his new sibling.