I am reading the short story "Stranger in Paradise" by Isaac Asimov. I will try to build some context for those who have not read the story or need a revision. 

The story is set in a futuristic world that has suffered from some unspecified "Catastrophe". In this post-catastrophe world, traditional family structures and monogamous relationships are considered archaic, out of fashion, and socially disgusting to some extent. Not criminal, but way out of the socially acceptable structure. 

The story deals with two brothers, children of the same parents—mother and father both—but this arrangement is described in the story as highly unusual. The brothers make every effort to stay as separated as possible, to avoid being identified together in society, as apparently that brings them the greatest shame and embarrassment. We see this in the story through several characters who exclaim upon finding out about their relationship that it's unfortunate. They even resent their parents for "repeating".

Some other facts about this world that are shown to us are that the children are not raised by their biological parents. Instead, they are raised in Creches. There is some genetic selection going on in these Creches, such as autistic children being either aborted or "cancelled" post-birth.

These are the facts. Now, what could explain this? Why in any world would a sibling relationship be considered shameful? The story, as short as it is, does not fill in any background, so we are left to deduce or speculate.

  • 9
    Isn’t one purpose of science fiction to explore what-ifs?
    – Jon Custer
    Apr 13 at 15:17
  • 2
    My recollection is I assumed it was to maximize genetic diversity, but it's been decades since I read it so I can't post that as an answer.
    – DavidW
    Apr 13 at 15:18
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    It's a genetic diversity taboo. In reality it's not that big of a difference as siblings might pass on different sections of their parents. Have you ever heard maybe a divorced person bragging or being complimented about their contributions to the gene pool by having a non repeating co-parent for each kid? Apr 13 at 17:09
  • @JonCuster indeed, but the story is clear in its stance that the change in family structures is something that was only a result of the Catastrophe. So in the author's world construction, this phenomenon is implied as a emergent property, not an intrinsic one which makes us question, rationally speaking, if such a property could actually emerge from some assumed nature about the unspecified Catastrophe, and if so, how?
    – sarthak-ag
    Apr 14 at 5:56
  • @lucasbachmann that's ... a strange brag. I have certainly not heard this before, so thanks for sharing!
    – sarthak-ag
    Apr 14 at 6:01

1 Answer 1


The nature of the world post-'catastrophe' is that it lacks genetic diversity. We're not told what caused this apocalypse, but it seems to have resulted in humanity being reduced to a very small population base (perhaps a few hundred individuals?) and only now returning to being a viable population by actively avoiding inbreeding. Two individuals having a second child together, known as 'repeating', makes it far more likely that future offspring in the community will have physical and health defects, which is why it's discouraged.

As it was-It didn't make it easier that they had played together as youngsters, and had shared the earlier stages of education in the same creche through some successful maneuvering on the part of Mother. Having borne two sons by the same father and having, in this fashion, reached her limit (for she had not fulfilled the stringent requirements for a third), she conceived the notion of being able to visit both at a single trip. She was a strange woman.

Note that while women are legally restricted to having only two children, having a second child with the same man is considered to be a social faux-pas, although not outright illegal. This suggests that the actual need to prevent multiple births has passed (or is closed to passing) and the taboo is more cultural than it is practical.

Dmitri said, "Your brother?"

"My father," said William, "had two boys by the same woman-my mother. They were eccentric people."

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    @DJClayworth - If genetic diversity was a big issue, but resources were also an issue then restricting birth numbers makes sense. And if you restrict birth numbers, you need to make every single one count from a genetic diversity POV.
    – Valorum
    Apr 13 at 15:54
  • That would seem to show a serious misunderstanding of genetic diversity, whether on the part of the author, the characters in the story, or the reader. The genetic diversity of the population is the same whether an individual has two offspring by one partner or by two different partners. Either way they contribute 50% of their own genes to the next generation with each mating. Those same genes remain in the population gene pool no matter where the other 50% came from in each child. It could reduce the diversity if they were prevent from breeding at all, but that'd be a different story.
    – Ethan
    Apr 13 at 21:24
  • @Ethan - It's far better to breed with someone who shares a lesser amount of the same genes. 50% is better than 100%, obviously
    – Valorum
    Apr 13 at 21:27
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    You may be thinking of a different concept, the recessive lethal load. But that is an entirely separate issue from genetic diversity, which is a property of the population rather than the individual.
    – Ethan
    Apr 13 at 22:59
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    I think the story does have strong hints towards the practice of genetic selection going on in the society, but I took it to mean they are obsessed with selecting the best genes for faster human progress. I had not considered that it is possible this society is suffering from stressed natural resources due to the Catastrophe which would force them to adapt their reproduction patterns to maximize genetic diversity, given a constant population size. I am inclined to accept this as the answer if no better answer pops up.
    – sarthak-ag
    Apr 14 at 6:13

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