Looking for a short-story or maybe a novella set after a nuclear war. The war is over and scientists realize that the human race will never breed true because of fallout causing mutations. It ends something like this, And the night flew out of Asia on illimitable wings. I read it in the 90s but it was older and was part of a short-story collection. That’s all I remember.
Based on purely the last part, it looks like it's "Heirs Apparent", by Robert Abernathy, as described on Goodreads:
A brief time after the War finally destroys the world, the last capitalist and the last communist have a showdown. Bogomazov, (who is, unlike the Russian in “One Thousand Miles Up,” a Party member) stumbles onto a small rural village in Russia and is horrified to find that it’s being led by an American GI who, at the moment he is introduced, is literally beating a gun mount into a plowshare. His name is Leroy Smith, and irony of his last name and his new profession is noted (a similar pun on Smith/blacksmith having been made in Bill Brown’s goofy “The Star Ducks” of 1950, which, by the by, is inexplicably far and away the most popular post on this blog). Smith doesn’t care about reviving the war, supposing that nothing is left of either American or the Communist Party, but Bogomazov is less interested in starting anew, and has him arrested.
Just so we are clear on the message, the story ends by noting that “In the West the light faded, and night fell with the darkness sweeping on illimitable wings out of Asia.”