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hominid which replaces its ancestor throughout Eurasia and Africa. Called Homo heidelbergensis , this creature has a much bigger brain, possibly 25 per cent bigger than late Homo erectus . Its brain was almost as big as a modern person’s. Yet not only did it go on making hand axes and very little else; the hand-axe design sank back into stagnation for another half a million years. We are used to thinking that technology and innovation go together, yet here is strong evidence that when human beings became tool makers, they did not experience anything remotely resembling cultural progress. They just did what they did very well. They did not change.
    Bizarre as this may sound, in evolutionary terms it is quite normal. Most species do not change their habits during their few million years on earth or alter their lifestyle much in different parts of their range. Natural selection is a conservative force. It spends more of its time keeping species the same than changing them. Only towards the edge of its range, on an isolated island, or in a remote valley or on a lonely hill top, does natural selection occasionally cause part of a species to morph into something different. That different sport sometimes then spreads to conquer a broader ecological empire, perhaps even returning to replace the ancestral species – to topple the dynasty from which it sprang. There is constant ferment of change within the species’ genes as it adapts to its parasites and they to it. But there is little progressive alteration of the organism. Evolutionary change happens largely by the replacement of species by daughter species, not by the changing of habits in species. What is surprising about the human story is not the mind-bogglingly tedious stasis of the Acheulean hand axe, but that the stasis came to an end.
    The Boxgrove hominids of 500,000 years ago (who were members of Homo heidelbergensis ) had their ecological niche. They had a way of getting food and shelter in their preferred habitat, of seducing mates and rearing babies. They walked on two feet, had huge brains, made spears and hand axes, taught each other traditions, perhaps spoke or signalled to each other grammatically, almost certainly lit fires and cooked their food, and undoubtedly killed big animals. If the sun shone, the herds of game were plentiful, the spears were sharp and diseases kept at bay, they may have sometimes thrived and populated new land. At other times, when food was scarce, the local population just died out. They could not change their ways much; it was not in their natures. Once they had spread all across Africa and Eurasia, their populations never really grew. On average death rates matched birth rates. Starvation, hyenas, exposure, fights and accidents claimed most of their lives before they were elderly enough to get chronically ill. Crucially, they did not expand or shift their niche. They remained trapped within it. Nobody woke up one day and said ‘I’m going to make my living a different way.’
    Think of it this way. You don’t expect to get better and better at walking in each successive generation – or breathing, or laughing, or chewing. For Palaeolithic hominids, hand-axe making was like walking, something you grew good at through practice and never thought about again. It was almost a bodily function. It was no doubt passed on partly by imitation and learning, but unlike modern cultural traditions it showed little regional and local variation. It was part of what Richard Dawkins called ‘the extended phenotype’ of the erectus hominid species, the external expression of its genes. It was instinct, as inherent to the human behavioural repertoire as a certain design of nest is to a certain species of bird. A song thrush lines its nest with mud, a European robin lines its nest with hair and a chaffinch lines its nest with feathers – they always have and they always will. It’s innate for them to do so. Making a teardrop-shaped sharp-edged