Meta: ISFDB. This novelette appeared first in new wave flagship New Worlds, August 1966, edited by Michael Moorcock. It was nominated for the Nebula in 1968. I’ve read it in The Doors of His Face, the Lamps of His Mouth and Other Stories, my review here.
Humans design their children to fit on special worlds – the protagonists are catlike enduring temperatures far below freezing water and breathing methane. As their original world is eradicated by a Nova they have to terraform – well, to freeze in this case – a new planet over the course of a couple of thousand years.
Sooner or later, the main protagonist Jerry and his lover witness the death of the biosphere and discover intelligent life on the planet and they know that it won’t be able to adapt to the end-stage. It remembers me of Do Androids Dream of Electric sheep with the morale question of killing intelligent life that you brought into existence.
It is a humanistic, melancholical story of colonialization and in contrast to The Doors of his Face or A Rose for Ecclesiastes a hard SF story whereas the other two could easily be set in contemporary world.
I wouldn’t say that it is a typical New Wave story; it is quite atypical for Zelazny, having no mythical background or embedded literaric references. But it is less confusing and an easier read than many other Zelazny stories, although it has a bit too predictive ending.