He marries his daughters, and they give him more daughters, and on and on it goes.
– Edison Tollett

During one of my usual afternoon discussions with fellow graduate students, we strayed on the precarious path of incest and argued as to where incest would fit on the nature vs nurture spectrum. I preferred to attribute the cultural embargo on incest to nurture, as incest had been widespread in antiquity, whereas my friend was of the opinion that the incest taboo is hard-wired in human beings, citing the near-universal forbiddance of sexual relations within close family.

This made me wonder about the sustainability of a population where the only means of population growth (for whatever reason) is incest. Those of you who watch/read Game of Thrones will be able to think of just such a population, the Craster’s keep. Craster (who the above quote refers to) is an old…