I feel towards you.
But marriage means children, and you are biologist enough to know
about Earth's genes--"

"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