‘And it’s more than enough time for natural selection to have shaped us, if we had given it the chance. The frozen imagination of the Coalition kept most of humanity in a bubble of stasis. But out in the dark, sliding between those islands of rock, it was a different matter: nobody could have controlled what was happening out there. And with time, we diverged.

‘After the first humans had left Earth, most of them plunged straight into another gravity well, like amphibious creatures hopping between ponds. But there were some, just a fraction, who found it preferable to stay out in the smoother spaces between the worlds. They lived in bubble-colonies dug out of ice moons or comets, or blown from asteroid rock. Others travelled on generation starships, unsurprisingly finding that their ship-home became much more congenial than any destination planned for them by well-meaning but long-dead ancestors. Some of them just stayed on their ships, making their living from trading.’

‘My own people did that,’ Futurity said. ‘So it’s believed. The first Engineers were stranded on a clutch of ships, out in space, when Earth was occupied. They couldn’t go home. They survived on trade for centuries, until Earth was freed.’

‘A fascinating snippet of family history,’ Tahget said contemptuously.

Poole said, ‘Just think about it, acolyte. These Hairy Folk have been suspended between worlds for millennia. And that has shaped them. They have lost much of what they don’t need - your built-for-a-gravity-well body, your excessively large brain.’

Futurity said, ‘Given the situation, I don’t see how becoming less intelligent would be an advantage.’

‘Think, boy! You’re running a starship, not a home workshop. You’re out there for ever. Everything is fixed, and the smallest mistake could kill you. You can only maintain, not innovate. Tinkering is one of your strongest taboos! You need absolute cultural stasis, even over evolutionary time. And to get that you have to tap into even more basic drivers. There’s only one force that could fix hominids’ behaviour in such a way and for so long - and that’s sex.’

‘Sex?’

‘Sex! Let me tell you a story. Once there was a kind of hominid - a pre-human - called Homo erectus. They lived on old Earth, of course. They had bodies like humans’, brains like apes’. I’ve always imagined they were beautiful creatures. And they had a simple technology. The cornerstone of it was a hand-axe: a teardrop-shape with a fine edge, hacked out of stone or flint. You could use it to shave your hair, butcher an animal, kill your rival; it was a good tool.