I'm looking for novel, written between about 1955 and 1965, touching on what it means to be human. The idea is explored through a human/humanoid marriage, and subsequent pregnancy and murder. I believe it was by a major author and written sometime around the release of "The Bramble Bush" since that novel/movie also dealt with something of the same themes in a more mainstream way.
The humanoids in this book had tails, which was the only outward feature that distinguished them from humans. They were considered to be animals, even though many spacers kept them as local "wives." A retired spacer wants to return home, bringing his (decreed) less-than-human long-term companion with him. This, because she isn't "human," is forbidden by law.
In the course of determining their future, she reveals that she is pregnant by him. He believes that this proves her humanity, but he is yet again refused permission to bring her back to Earth. Eventually he kills his own offspring to provoke a trial; if he's found guilty, she must be human.
Pretty radical, but a thought-provoking read, and I'd like to read it again.