Robert Silverberg: The Happy Unfortunate: Humanity is forced to breed a new species - of humans
(Reklamlänk)
The Happy Unfortunate was published first in Amazing Stories in 1957 and explores the angst caused when the human race reaches into space but at the cost of needing to breed a new species; specialized 'spacers' who can withstand the tremendous rigors of acceleration. Of course they must leave behind loved ones.
