Able hadn’t been much older than Pilgrim was now when, with Bearbane as his guide, he had led a small expedition to an ancient city mound in the high western desert of the New Territories and disinterred the remains of bears from the city’s burial ground. Layers of bones packed one on top of another. More than twenty thousand years of history set out in an orderly sequence. Able’s detailed measurements of bones from different layers revealed that bears had already been smaller and more slightly built than their feral ancestors when they had begun to construct their first cities, and had changed very little throughout the city-building epoch. Contrariwise, similar measurements of bones from contemporary specimens showed that, a mere six centuries years after the fall of their civilisation, bears had become larger and more robust. The findings had given Able a famous example of two extremes of selective adaptation in a single species. Bear civilisation had been stable and unchanging for more than thirty thousand years, so any selective pressures would have been stable and unchanging too. But after it had collapsed, changes in the habit and diet of surviving bears, and competition for scarce resources and suitable mates, meant that only the strongest individuals were likely to survive and reproduce.

In some of the oldest layers the skeletons of people had been found next to those of bears. The remains of favoured slaves, killed when their masters had died, and buried with them. Measurements of those bones confirmed the findings from so-called slaughter pits where the bones of thousands of slaves were jumbled together in no especial order: people enslaved by bears, even those who had lived and died twenty thousand years ago, were anatomically indistinguishable from contemporary people. Most likely they had not endured the lash as dumb brutes, but had suffered as any ordinary person might suffer.

Bearbane was smiling as a memory surfaced. ‘I haven’t seen Able in a long while, but he still writes to me.’

‘I have some news about him. And I am afraid that it is not good,’ Pilgrim said.

Bearbane didn’t appear to have heard him, saying, ‘Such interesting letters about his work. I should write back …’

‘He has returned to the Mother, Grandfather.’

‘Who has?’

‘Your friend. Able. It was mercifully quick. He was felled by a thunderbolt to the brain and passed the next day.’

‘Are you sure? I know he wrote to me last year. I think it was last year …’

‘I was with him when he died. I was his secretary. You wrote the letter of recommendation that convinced him to hire me.’

‘I did?’

Pilgrim felt a pang of sorrow, watching the old man try to puzzle it out.

‘Well, never mind,’ Bearbane said at last. ‘We’ll walk in the garden, and you can tell me what you have been doing.’