Teranesia

Prabir pondered this for a while. ‘It’s a counterfactual defence. Once you have the São Paulo gene, you can block predators that have never even tried to prey on you, in your own history. And so long as you maintain the defence, they won’t bother evolving in that direction, because they can see that there’s no point. It’s like a simple chess program: no elaborate strategies copied from grand masters, just the power to look ahead a few moves and assess the consequences. If brute force computation reveals a strategy – like castling, say – that gives a medium-term advantage over all possible moves by its opponents, the program will use it. And it will never reverse it, even if there’s no immediate threat, because it can look far enough ahead to see that any back-down would be exploited.’

Grant was beginning to look slightly uncomfortable. ‘You don’t seriously believe that’s what’s happening, though?’

‘Absolutely not. He’ll run the experiment on the synthetic chromosome, and prove himself wrong.’

Grant made a half-hearted sound of agreement, as if she was afraid that excessive confidence might be tempting fate.

Prabir said, ‘I meant to ask you: did you get the results of the RNA analysis of the dormant adults?’ The last he’d heard, it had been running overnight.

‘Yeah. There’s a peptide being produced that’s virtually identical to a well-known hormone that puts the adults of certain temperate species of butterflies into diapause when they hibernate over winter. And the alteration in the texture and pigmentation of the wings seems to have followed from a cascade of gene activity very similar to one that happens in ordinary metamorphosis. It’s all pretty much what I’d expected: just a few existing tricks redeployed.’

‘OK. But redeployed to what end? I know it’s pointless now, because the adults have already laid their eggs externally, but could this be a throwback to a species that used to reproduce via parasitic larvae?’ Maybe the gene resurrection idea could still be salvaged, after all.

Grant shook her head. ‘Not unless it’s gone even more awry than that. The males are all doing it too.’

Prabir held the guard rail and pushed against it, trying to unknot his shoulders. ‘If the gene didn’t start off as something every species has for mutation repair, we still have to account for its spread from the butterflies to everything else.’ He turned to Grant, smiling disarmingly, hoping she’d suffer a little more frivolous speculation. ‘Just for argument’s sake: if Furtado was right, maybe the São Paulo gene saw this as an easy way to get copies of itself into the fruit pigeons.’

Grant didn’t respond immediately; Prabir assumed she was thinking up a suitably withering reply.

‘I found something else in the RNA analysis,’ she said.

‘Yeah.’

‘Large amounts of an endonuclease – an enzyme for cutting and splicing DNA – being produced throughout the bodies of the dormant adults. I haven’t characterised it any further yet …’ She trailed off.

Prabir said, ‘But if it’s the right kind of endonuclease, it might be perfect for the job of splicing the São Paulo gene into the genome of the fruit pigeons?’

Grant nodded, and continued reluctantly. ‘The fraction of DNA and endonuclease that survived digestion and entered the bloodstream would always be tiny, though I suppose it could be packaged in something like liposomes to protect it, and help it get absorbed by the wall of the gut. There’s then another hurdle to get the gene into the ovaries or testes. This might be the transmission route, but the whole picture’s not clear, by any means.’

Prabir looked back across the water; he could still see Teranesia’s volcanic cone in the distance. ‘Everything else could be a throwback, couldn’t it? If mimcry was once used to get parasitic larvae into the fruit pigeons, then if the genes for that have been reactivated now, pointlessly, in egg-laying females, they might also have been reactivated in males – simply because the switch isn’t functioning properly.’

‘I suppose so.’

‘And there are other uses for endonucleases, aren’t there? It might be a coincidence that the endonuclease gene is switched on at the same time as the others?’

‘It might.’

Prabir laughed suddenly. ‘Listen to me. We’ve been to Teranesia, we’ve been to the source, and I expect everything to fall into place in a day. I’ve gone twenty-one years without an answer. I can wait a little longer.’

He glanced down at the graphic of SPP in Furtado’s article, which was cycling through sixteen of the conformations it could adopt, binding to each of the four bases in the old strand while adding each of the four to the new. Between them, these sixteen simple transformations could generate every conceivable change: as the old strand was broken apart and the new one constructed, the potential existed for the organism to become anything at all.

And from that limitless sea of possibilities, what marvellous inventions did the São Paulo gene pluck?