Do you have a source for "natural tendency for humans to be less attracted to close relatives than to others"? I am interested.
One mechanism is the MHC complex
There are other mechanism that prevent siblings that lived together as children from developing romantic interest in each other as well. As a result most cases of incest between siblings are not by siblings that lived together as children.
That has impressive applications on why foreigners or "exotic" people have a bonus placed on them for desirability. I must say I did know about MHC mechanism, and the studies done on birds, but not the human one. Also I did not connect the two.
Thanks!
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