In the end Macintosh tacitly admitted that the ethical behaviour pattern of Samaritan II, which refused to throw itself overboard to save a sandbag, and so took the sandbag to the bottom with it as well, was unsatisfactory. He developed Samaritan III, which not only refused to sacrifice itself for an organism simpler than itself, but kept the raft afloat by pushing the simpler organism overboard.

‘Look at it, man,’ he cried to Goldwasser, awed by his own handiwork, as they watched Samaritan III ruthlessly toss first a sandbag and then a sheep over the side. ‘That’s a terrible sight, Goldwasser, a great and terrible sight. All the pity and the grandeur of man’s struggle for survival are there. And yet this same Samaritan III when faced by Man, in the person of Sinson, does not hesitate to cast itself away. Perhaps we have an analogy here with the human mind’s intuition of the divine. What we have beyond any doubt is a skeletal yet fundamentally accurate model of behaviour that is both ethical and effective.’

Goldwasser sighed. If there was one thing he found less congenial then believing himself stupider than Macintosh it was finding himself cleverer.

‘Try putting two Samaritan IIIs on the raft together,’ he suggested gloomily.

Macintosh put two Samaritan IIIs on the raft together, and the result drove him back on to the defensive. At first he tried to claim that it was entirely in accordance with good sense and natural justice that both Samaritan IIIs should throw themselves overboard.

‘There is a certain nobility about their choosing to perish together which recalls the high ethic of romantic tragedy. I was thinking of Romeo and Juliet.’

Goldwasser rubbed his chin nervously, and looked anywhere but at Macintosh, in a way that powerfully undermined Macintosh’s arguments. Macintosh made a minor adjustment to the Samaritans, with the result that instead of throwing themselves overboard, they threw one another. He invited Goldwasser in to watch as the two ethical machines seized one another in a powerful lock and hurled one another into the water.

‘Aye,’ said Macintosh, ‘we see before us all the pity and the terror of the human condition, whose inexorable logic requires men to struggle with their peers for life even to the point of mutual extinction.’

‘It sounds like the First World War,’ said Goldwasser.

‘Exactly.’

‘Or an ape trap.’

‘An ape trap?’

‘A bottle with a banana in it. The ape puts his hand in and seizes the banana, which makes his fist too big to get out of the bottle. Compelled by the inexorable necessity of the simian condition to hold on to the food, the ape remains attached to the bottle and dies of starvation.’