Teranesia

sprouted twigs bearing half a dozen white blossoms swollen with fruit. The cluster of twigs and fruit fell at the bird’s feet, landing on the large, solid branch where it was perched. It proceeded to attack one of the fruits, chewing through the leathery hull, which had not quite ripened to the point where it would split open and spill the seeds, the almonds, on to the ground.

Grant came over to see what he was looking at. Prabir described what he’d observed so far. The bird had extracted one of the almonds from the fruit, and was performing an even more elaborate routine to penetrate the hard shell.

She said, ‘This part’s old hat: its a famous case of specialisation for a food source.’ The bird had broken away part of the shell, and was now holding the nut with one foot while it used the sharp, hooked part of its upper beak to tear out fragments of the kernel; a tongue like a long-handled pink-and-black rubber stamp darted out to pick up the pieces and take them into the bird’s mouth. ‘Going for the unripe fruit is new, though.’

‘So it doesn’t have to wait for the nuts to fall. Which means the teeth are there to help it stay off the ground?’

‘I suppose so,’ Grant conceded. ‘But there might have been any number of reasons in the past why that was a good idea. It doesn’t require co-evolution with the ants.’

Prabir turned to her. ‘If you’d come to this island knowing nothing about its history, nothing about the ordinary fauna of the region—if you’d dropped in out of the sky in a state of complete ignorance about this entire hemisphere—what would you think was going on here?’

‘That’s a stupid question.’

‘Humour me.’

‘Why? What point is there in ignoring the facts?’

Prabir shook his head earnestly. ‘I’m not asking you to do that. I just want you to look at this afresh. If you’d just arrived from the insular British Isles with an immaculate, theoretical training in evolutionary biology, but no contact for a thousand years with anyone east of Calais, what would you conclude about the plants and animals here?’

Grant folded her arms.

Prabir said, ‘I’m withdrawing my labour until you answer me. Forgetting all the history you know, what does this really look like to you?’

She replied irritably, ‘It looks to me as if the affected species originally shared territory with all the others, then became isolated on some remote island and co-evolved separately for a few million years—and now they’re being progressively reintroduced. OK? That’s what it looks like. But on what island is this meant to have happened?’ She spread her arms. ‘It didn’t happen here: you can vouch for that yourself. There’s no island in the whole archipelago sufficiently isolated, and sufficiently unexplored.’

‘Probably not.’

‘Certainly not.’

Prabir laughed. ‘OK. There’s no such island! All I’m saying is, when the account you’ve just given sounds so much simpler than a hundred separate genes in a hundred separate species marching back from the past in perfect lock-step—I have a lot of trouble seeing how it can’t be telling us something about the truth.’

Grant’s expression softened, her curiosity getting the better of her defensiveness. ‘Such as what?’

‘That, I don’t know.’

Prabir had rewritten the image-processing software to run directly on Grant’s camera. In the afternoon, she found the camouflaged fruit pigeons all around them.

Fluttering across the viewfinder between the pigeons were the butterflies. The wing patterns had changed dramatically—the dappled imitation of foliage and shadows they’d acquired was far less striking, far less symmetric, and far more variable from insect to insect than the old concentric bands of green and black—but when Grant finally captured one and Prabir saw the body, he knew they were the descendants of the insect he’d first seen pinned to a board in his father’s office at the university.

The tranquilliser darts were useless for insects, but Grant had a spray based on wasp venom that could temporarily paralyse the butterflies without killing them. Using a net to keep their victims from falling to the ants, they managed to collect half a dozen live specimens of both the pigeons and the butterflies.

Back on the boat, Grant killed and dissected one of the male pigeons, removing the testes and then working under a microscope to extract stem cells and various stages of maturing spermatocytes. She was hoping to catch the Sao Paulo protein in the act, though given the uniformity of the pigeons it seemed unlikely that it was still producing radical changes in their genome.

Prabir left her to it and stood out on the deck, staring back into the harmless shadows of the jungle, numb with relief as he realised how painlessly the day had passed. Between the distracting riddle of the altered species and the sheer physical effort of gathering samples, he’d had little time or reason to dwell on the significance of the place. And that was how it should be. He’d already mourned his parents, in the camp, in Toronto, and he’d recounted their triumphs a thousand times for Madhusree. There was nothing to be done here, nothing to be remembered, nothing to be learnt but the secret of the butterflies. He refused to imagine them trapped on the island. In the only sense that they survived at all, they’d left in the very same boat as he had.

And though Teranesia had proved to be no more dangerous than the other islands, he was still glad that he’d kept Madhusree away. She might resent his intervention for years to come. She might accuse him of standing between her and the memory of her parents. But the alien jungle would have meant even less to her than it did to him, and he’d spared her the pointless anguish of digging through the ruins of the kampung. His mother had told him, ‘Take her away! She mustn’t see!’ He’d completed what he’d begun when they’d set out on the boat. It had been a long trip, but now it was over.

Grant emerged from the cabin frowning, carrying her notepad.

‘More news from Sao Paulo,’ she said. ‘They’ve refined their model.’

‘And?’

She propped the notepad on the guard rail in front of Prabir; it was displaying a graphic of a couple of large molecules bound to strands of DNA. ‘I don’t know what to make of this. I was hoping they’d find evidence that some part of the protein resembled a transcription factor, and recognised disabled promoters—’

Prabir stopped her. ‘I used to know all these terms when I was a kid, but I’m pretty hazy now. Can you —?’

Grant nodded apologetically. ‘Promoters are sequences of DNA that sit next to the coding region of a gene, which is the part that actually describes the protein. Transcription factors bind to promoters to initiate the copying of the gene into RNA, which is then used to make the protein: to “express the gene”.

‘If a gene is accidentally duplicated, mutations that build up in the promoter of one copy might eventually stop that copy from being expressed. To identify a gene that’s become inactive like that, you’d need something that was capable of binding to a damaged promoter—something roughly the same shape as a transcription factor, but a little less fussy. And then to reactivate the gene, there’d be a number of possible strategies, either working base by base to repair point mutations in the promoter, or snipping the whole thing out and splicing in an intact version.’

Prabir said, ‘OK, that all makes sense. Now what have the modellers found?’

Grant hit a button on the notepad and animated the graphic. ‘This bloody thing just crawls along causing havoc during DNA replication. What normally happens is: the double helix unwinds, the two strands separate, and DNA polymerase comes along and stitches together a new complementary strand for each of them, from free-floating bases. What the Sao Paulo protein does is slide along each single strand, cutting it up into individual bases, while splicing together a whole new strand of DNA to take its place. Then DNA polymerase comes along and duplicates that.’

Prabir took the notepad from her and slowed down the animation so he could follow the steps. ‘But what’s the relationship between the old sequence and the new sequence?’

‘Basically, the new one is the old one, plus noise. SPP changes shape as it binds to each base of the original strand—it assumes a different conformation depending on whether it’s cutting out adenine, guanine, cytosine, or thymine—and that in turn determines the base it adds to the new strand. But the correlation isn’t perfect; there are some random errors introduced.’

Prabir laughed, disbelieving. ‘So it’s just an elaborate, self-inflicted mutagen? These creatures might as well