Teranesia

be bathing their gonads in radiation or pesticide?’

Grant replied dejectedly, ‘That’s what they’re claiming.’

He replayed the animation. ‘No. This is crazy. If you wanted to add a few extra random errors to your offspring’s DNA, would you take the easy way out and just alter your DNA polymerase slightly, so it made occasional mistakes—or would you invent a whole new system like this for making deliberately flawed single-strand copies?’

‘Well, exactly,’ Grant said. ‘And even if you had a good reason to take that approach, the whole protein’s vastly over-engineered. There are commercial enzymes that do something similar, and they’re about one-hundredth the molecular weight.’

‘Maybe there’s a bug in their software. Or maybe there’s some logic to the changes, some pattern that they simply haven’t noticed.’

Grant shrugged morosely. ‘They’ve synthesised some of the protein for real now; they’re doing test-tube experiments as we speak, to try to confirm all this.’

She seemed to be taking it all too much to heart. Prabir said, ‘You know that the things we’ve seen here can’t be explained by random mutations. Maybe there’s still some way this can be compatible with your theory. But whatever’s going on, at least we’re closing in on it.’

‘That’s true.’ She smiled. ‘They have synthesised protein in Sao Paulo, and I have cultured fruit pigeon spermatocytes. By morning they’ll know what happens in a test tube, and we’ll know what happens in a living cell.’

When Prabir woke, this prediction had been fulfilled. Grant had been up since three o’clock trying to make sense of the results.

The experiments in Sao Paulo had confirmed the computer model: fed a few hundred different test strands of DNA, the protein had chopped them up and synthesised new strands of exactly the same length, copying the original sequence but introducing random errors. Another group, in Lausanne, had repeated the work and found the same thing.

Grant had detected RNA transcripts for the Sao Paulo protein in the pigeon spermatocytes, which implied that the protein itself was being made in the cells; she had no direct test for it. But when she compared sequence data for cells before and after meiosis, the error rate was about a thousand times less than for the two experiments in vitro.

She said, ‘There has to be a second protein, some kind of helper molecule that modifies the whole process.’

‘So they need to look harder at the sequence data?’ Prabir suggested. ‘The gene for it must be in there somewhere.’

‘They’re looking. SPP alone is a bit like a pantograph with a whole lot of superfluous hinges. So maybe this is something that binds to it and stabilises it—not enough to produce perfect copies, but enough to allow its internal state to reflect the last few dozen bases to which it was bound.’

Prabir opened his mouth to say, Turing machine, but he stopped himself. Most processes in molecular biology had analogies in computing, but it was rarely helpful to push them too far. ‘So it could recognise a sequence of something like a promoter, even though it only binds to one base at a time?’

‘Maybe,’ Grant agreed cautiously. ‘They’ve also got hold of samples from the Ambon fruit pigeon, and they’re going to see what pure, synthetic SPP does to an entire chromosome, in the presence of nothing but a supply of individual bases.’

As they waded ashore, Prabir looked down into the warm, clear water where he’d swum with Madhusree, then across the dazzling white beach where they’d played. He wasn’t just cheating her out of a role in the study of the butterflies, he was depriving her of the chance to demystify the island, to purge it of its horrors the way he was doing for himself.

But he could never have brought her back here. He could never have undone the one good thing.

Grant wanted to collect specimens of the butterfly’s other stages, so they spent the morning doing nothing but searching appropriately succulent leaves for the spiked larvae, and the branches of the same trees for pupae. The original versions would not have been hard to spot: both had been covered in bright-orange patches, warning colours to signal their toxicity. Grant found signs of leaf damage that looked promising, but there were no culprits nearby. If the larvae had switched strategy and opted for camouflage that was as efficient as the adults’, their movements would be far too subtle for the image-processing software to detect.

They stopped and ate lunch in the middle of the forest, in a rare spot where the ground was rocky enough to keep the shrubs at bay. Prabir still didn’t feel safe sitting down until he’d sprayed a cordon of insect repellent on the ground; the ants were never content to stay inside the orchids, waiting for easy prey. He wasn’t sure why they didn’t swarm up the trees and take nestlings; maybe they were lacking some crucial adaptation for the task, or maybe it just wasn’t worth the energy.

Grant said, ‘So your whole family was here for three years, from 2010? Was your sister born on the island?’

He laughed. ‘We weren’t quite that isolated. We went to Ambon on the ferry four times a year. And we flew down to Darwin for the birth.’

‘Still, it must have been a rough place to raise a young child.’ Grant added hastily, ‘I’m not criticising your parents. I’m just impressed that they could cope.’

Prabir shrugged. ‘I suppose I took that for granted. I mean, the people in small villages on the other islands had better access to transport, clinics they could get to, and so on. But we had a satellite link, which made it easy to forget the distance. I even had lessons from a school in Calcutta; they’d set up a net service for kids in remote villages, but I could join in just as easily.’

‘So at least you had some friends your own age through the net.’

‘Yeah.’ Prabir shifted his position on the rock, suddenly uncomfortable. ‘What about you? What were your school days like?’

‘Mine? Very ordinary.’ Grant fell silent for a while, then she took out her camera and began scanning the branches around them.

She said, ‘The butterflies spend a lot of their time quite high in the canopy. Maybe they lay their eggs there.’ She lowered the camera and asked casually, ‘What are you like at climbing trees?’

‘Seriously out of practice.’

‘It’s like riding a bicycle. You never forget.’

Prabir gave her a stony look. ‘You’re the field biologist, remember? I’m the desk zombie. And I don’t care how ancient you are: you’re twice as fit as I am.’

‘You put that so gallantly.’

Prabir said flatly, ‘I’m not doing it! The deal we made in Ambon—’

Grant nodded effusively. ‘OK, OK! I only asked because I’m not used to judging the strength of the branches of these species. I thought you might be more confident, since you must have climbed them as a kid. I’ll go back to the boat and get a rope—’

‘A rope? You’re not serious?’

‘I had a bad experience in Ecuador,’ she admitted. ‘I broke a lot of bones. So I’m ultra-careful now.’

Prabir’s resentment faded. There was a principle at stake, but he didn’t want to be petty and sadistic. ‘I’ll do it, but you have to pay me. Ten dollars a tree.’

Grant considered this. ‘Make it twenty. I’ll feel better.’

‘With a conscience like that, who needs labour laws?’

Grant selected a nutmeg tree. Prabir took off his boots and rolled up his trouser legs. He hesitated, unsure how to begin. The lowest branch of this tree was just above his head; he must have been able to scale a sheer trunk once, gripping the bark with his arms and legs—he’d even climbed coconut palms—but he felt certain he’d make a fool of himself if he tried that now.

He grabbed the branch and raised himself up, then hooked his feet around it and hung sloth-like for a while before figuring out how to right himself. It was a clumsy start, but once he was standing squarely on the branch, with a firm grip on the next one up, he was elated. The scent of the bark, the feel of it against his soles, was utterly familiar; even the view straight across into the other trees was far closer to anything he remembered than the view from the ground. He glanced down at Grant, not wanting to lose perspective, not wanting to be drawn back too