“You know how to see evolutionary patterns,” said Deborah. “You know how natural selection works, how different societies promote the survival of some traits and not others. And there have been no human scientists on that road before you.”

“Do I detect a desire to be rid of this old man?” asked Wheaton with a laugh.

“Do I detect a barely-concealed plea for validation?” asked Deborah. “You know I love you, and I’d like to think your work would not be possible without me to clerk for you. But that isn’t true, and besides, you can have the ship pop out an extra expendable to take notes and look things up for you. Much more efficiently and accurately than I would.”

“Very well, I suppose I can work without you,” said Wheaton. But he looked grumpy, and that seemed to be a concealment of an underlying hurt.

“One world offers me eyes,” said Deborah, “and the other offers you a chance to do seminal work. If Noxon and Ram succeed in changing the future of that world, you will be the only scientist to observe the alien society as it existed before human interference.”

“We won’t be doing much observation,” said Noxon. “Particularly if we reach them at a time when they’re already technologically ahead of us. We’ll skedaddle instantly then.”

“I’ve found that brave dead scientists don’t contribute as much as prudent live ones,” said Wheaton. “I’ll study what there’s time to study.”

“It’s where you want to go,” said Deborah.

“All things being equal. But . . . nineteen wallfolds. A species of merpeople! Either world will do for me.”

Deborah made no answer, even though both Noxon and Wheaton looked at her, waiting.

“You know I have a choice myself,” said Noxon. “There are two of me now. One who went through the nuclear blast but managed to heal from it. One who didn’t.”

“Which are you?” asked Deborah.

“I’m the one who was warned and saved from the blast,” said Noxon. “But my twin and I have worked it out. It’s quite simple, really. There’s some risk that he suffered damage to some or all of his gametes. The facemask heals damage it can detect, but it’s possible for gametes to be motile and yet not viable, or viable but mutated.”

“Ouch,” said Deborah.

“Mine, however, were unharmed,” said Noxon. “Not that there’s no risk of mutation or deformation—any gamete can be damaged by the vicissitudes of chance. But . . .”

“So you, Mister Pristine Sperm, will go where you think your seed will be most needed,” said Deborah.

“Not quite,” said Noxon. “Chances are that both of us will be able to reproduce successfully. But we want to invest my superior odds in a particular way.”

“I’m not sure why this is a matter for discussion with us,” said Wheaton.