"Intolerant yokel!" she cried, slapping his face. He didn't move or attempt to stop her. "I expected better from you, with all your pretensions of understanding. But all you can think of are the horror stories about the worn-out genes of Earth. You're the same as every other big, strapping bigot from the frontier planets. I know how you look down on our small size, our allergies and haemophilia and all the other weaknesses that have been bred back and preserved by the race. You hate—"
"But that's not what I meant at all," he interrupted, shocked, his voice drowning hers out. "Yours are the strong genes, the viable strains—mine are the deadly ones. A child of mine would kill itself and you in a natural birth, if it managed to live to term. You're forgetting that you are the original homo sapiens. I'm a recent mutation."
Lea was frozen by his words. They revealed a truth she had known, but would never permit herself to consider.
"Earth is home, the planet where mankind developed," he said. "The last few thousand years you may have been breeding weaknesses back into the genetic pool. But that's nothing compared to the hundred millions of years that it took to develop man. How many newborn babies live to be a year of age on Earth?"
"Why ... almost all of them. A fraction of one per cent die each year—I can't recall exactly how many."
"Earth is home," he said again gently. "When men leave home they can adapt to different planets, but a price must be paid. A terrible price is in dead infants. The successful mutations live, the failures die. Natural selection is a brutally simple affair. When you look at me, you see a success. I have a sister—a success too. Yet my mother had six other children who died when they were still babies. And several others that never came to term. You know about these things, don't you, Lea?"
"I know, I know ..." she said sobbing into her hands. He held her now and she didn't pull away. "I know it all as a biologist—but I am so awfully tired of being a biologist, and top of my class and a mental match for any man. When I think about you, I do it as a woman, and can't admit any of this. I need someone, Brion, and I needed you so much because I loved you." She paused and wiped her eyes. "You're going home, aren't you? Back to Anvhar. When?"
"I can't wait too long," he said, unhappily. "Aside from my personal wants, I find myself remembering that I'm a part of Anvhar. When you think of the number of people who suffered and died—or adapted—so that I could be sitting here now ... well, it's a little frightening. I suppose it doesn't make sense logically that I should feel indebted to them. But I do. Anything I do now, or in the next few years, won't be as important as getting back to Anvhar."
"And I won't be going back with you." It was a flat statement the way she said it, not a question.
"No, you won't be," he said. "There is nothing on Anvhar for you."