He said, ‘You know what I like most about being with you?’

‘No.’

‘Stealing this together.’ Prabir hesitated, afraid of sounding foolish. But if he couldn’t speak now, when could he? ‘Sex is like a diamond forged in a slaughterhouse. Three billion years of unconscious reproduction. Half a billion more stumbling towards animals that weren’t just compelled to mate, but were happy to do it—and finally knew that they were happy. Millions of years spent honing that feeling, making it the most perfect thing in the world. And all just because it worked. All just because it churned out more of the same.’ He reached down and slid his palm over Felix’s penis. ‘Anyone can take the diamond; it’s there for the asking. But it’s not a lure for us. It’s not a bribe. We’ve stolen the prize, we’ve torn it free. It’s ours to do what we like with.’

Felix was silent for a while, just smiling up at him. Then he said, ‘Do you know what an oxbow lake is?’

‘No.’

‘When a river meanders sharply, sometimes the water in the bend ends up cut off from the flow. The river throws off an oxbow lake. That’s how I’ve always thought of it: we’re in an oxbow lake, we’re not part of the flow. But the river keeps making those lakes. There’s something still in it, generation after generation, that makes it happen.’

Prabir conceded, ‘Maybe that’s a more honest way of putting it. We had no choice; we’re just stranded here by chance.’ He shrugged. ‘But I’m glad I’m cut off, I’m glad I’m stranded.’

Felix reflected on this, then suggested cryptically, ‘Maybe you’re not, though. Maybe it just looks that way.’

Prabir laughed. ‘You think I’m moonlighting as a sperm donor?’

‘No. But you have to ask yourself: why are there genes in the river that keep making the lakes? What does any lineage have to gain by retaining that trait, in the long run? Swapping the sex of the object of attraction might be the least risky way to make someone infertile; it’s less dangerous than messing with anatomy or endocrine function—and a hundred thousand years ago it might not even have entailed getting the crap beaten out of you.’

Prabir had his doubts, but he was willing to accept the premise for the sake of the argument. ‘What’s the advantage of being infertile, though?’

Felix said, ‘Under the right conditions, infertile adults might be able to contribute more to the survival of the lineage by devoting their resources to close relatives, rather than children of their own. It takes so long to raise a human child that it might be worth having the occasional infertile offspring as a kind of insurance policy—to look after the others if something happens to the parents.’

Prabir disentangled himself and sat on the side of the bed. His heart was pounding, and there was a red streak across his vision, but he’d pulled away without even thinking. He still lost his temper too easily, but through eight long years with Keith and Amita he’d trained himself to withdraw, not lash out.

‘Prabir? Shit. I didn’t mean—’ Felix swung his legs around and sat beside him.

Prabir waited until he could speak calmly. ‘I really set myself up for that one.’

‘Come on, you know I didn’t mean it like that.’

‘Didn’t you?’

‘No!’ Felix managed to sound both contrite and indignant. ‘Even if the theory’s true… all it’s describing is the survival of the trait through a statistical advantage. It says nothing about the actions of individuals.’ There was an awkward silence, then he conceded, ‘But it was pretty crass of me to bring it up like that. I’m sorry.’

‘Forget it.’ Prabir stared down at the worn linoleum at his feet, his anger draining away. ‘You know, in high school I used to try to start relationships with girls I thought Madhusree would look up to?’ He laughed, though the memory of it still made him cringe. ‘Which probably would have been enough to doom the entire endeavour, even if I’d been straight. And when I finally stopped kidding myself that there was any chance of that… I just felt like I’d fucked up again. I couldn’t even give her a sister-in-law with attitude, to make up for my stupidity in bringing her to Amita.’

Felix said, ‘You should have trusted her more. You should have known she didn’t need it.’

Prabir snorted derisively. ‘That’s easy to say now! But why should you trust a child to overcome being brought up by fools? Was I supposed to assume that she was genetically endowed with so much innate good sense that nothing anyone could do would harm her?’

‘Hmm.’ Felix seemed genuinely lost for a reply, though maybe he was just being diplomatic.

‘But you’re right,’ Prabir admitted. ‘Madhusree didn’t need role models. By the time we left Amita, I understood that. And I finally stopped worrying about all the ideology Amita would have tried to foist on me if she’d ever found out that I was gay. I started thinking about what it meant for me, instead of what it meant for everyone else.’ He stopped abruptly, his courage waning; he’d already made enough of a fool of himself.

But Felix squeezed his shoulder and said, ‘I’m listening. Go on.’

Prabir kept his eyes on the floor. ‘I thought: maybe I should be glad. Evolution is senseless: the great dumb machine, grinding out microscopic improvements one end, spitting out a few billion corpses from the other. If I’d dragged just one good thing clear of it—if I’d found a way to be happy that cheated the machine—then that was a kind of victory. Like dragging Madhusree clear of the war.’ He looked up and asked hopefully, ‘Does that make any sense to you?’

‘It makes a lot of sense.’

‘But you don’t believe it’s true, do you? You don’t believe I’ve cheated the machine.’

Felix hesitated, then made an exasperated noise, as if he’d been trapped into a choice between arguing with him or humouring him.

He said, ‘I don’t believe it matters.’

Prabir was suddenly sick of talking. He’d bared his soul, and it had brought them no closer. He took Felix by the shoulders and drew him down on to the bed.

‘Ah, that’s what I like: less theory, more practice.’ Felix kissed him deeply, then ran a hand down the centre of his body. ‘You’ve got a lot of catching up to do.’

Prabir said, ‘I’ll race you to the edge of the lake.’

‘I have a favour to ask you.’

Madhusree was washing the breakfast dishes; Prabir was drying. Felix had left, but they’d arranged to meet in the evening. Winter sunlight filled the kitchen, revealing every speck of dust and every imperfection on the room’s worn surfaces. Prabir felt utterly contented. He had no problems in his life, just invented complications. They were safe, they were happy. What more did he want?

He said, ‘Go ahead.’

‘I need some money.’

‘Sure. How much?’

Madhusree grimaced, bracing herself. ‘Five thousand dollars.’

‘Five thousand?’Prabir laughed. ‘What are you planning to do? Start a business?’

Madhusree shook her head apologetically. ‘I know, it’s a lot to ask.’ She added, deadpan, ‘That’s why I was so glad when Felix showed up last night. I’ve been waiting all week to catch you in a good mood.’

Prabir flicked her on the arm with the tea towel. ‘Don’t be impertinent. And it makes no difference. I’m always in a good mood.’

‘Ha.’

‘So what’s the money for?’

‘I should be able to pay you back within a couple of years. Once I’ve graduated—’

Prabir groaned. ‘You don’t have to pay me back. Just tell me what you want it for.’ He scrutinised her face; she stared back at him with exaggerated nonchalance, but she couldn’t quite pull it off. She was actually nervous.

He was worried now. ‘If you’re in some kind of trouble, just tell me. I’m not going to be angry.’

Madhusree said, ‘I’ve been invited to go on a field trip. A joint expedition being mounted by several universities. It’s twenty-one people, mostly postdocs, but they’re taking two undergraduates. Only the funding doesn’t really cover us, so we have to pay our own way.’