This public service announcement was brought to you by Star Wars, where things almost went horribly wrong between siblings Luke and Leia.
If you'd like to further explore this incestual possibility check out Splinter Of The Mind's Eye, a novel by Alan Dean Foster which was published in 1978 and takes place between Episode IV: A New Hope and Episode V: The Empire Strikes Back.
What would your father Annakin/Darth think of what you two are about to do?!
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Well you could eliminate roughly half the population to start with.