How many descendants are required before sexual relations is no longer incest ?

This is an ethical question, and is based on most societal systems rejecting incest, however if you follow the logic, then technically we are all related, so at what point is it no longer incest ?

  • From the evolutionary perspective, we may be all related but we don't have a single common ancestor so incest didn't have to occur in the past (since we evolved from a transitional hominid population, homo erectus instead of a single transitional hominid). – Cicero May 19 '15 at 4:44
  • From a biblical creationist perspective, earl man from the descendants of Adam and Eve (who technically aren't siblings) were allowed to do incest to populate the Earth, but then God banned it (I don't know the particulars, but this explicates it. – Cicero May 19 '15 at 4:45
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    I'm voting to close this question as off-topic because it does not appear to be about philosophy. Incest is a biological term, and has no intrinsic ethical value. There are ethical questions concerning incest, but this isn't one. If the question is "how many descendants ... before it's bad", it is primarily opinion based. – user2953 May 19 '15 at 7:21
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    @SanuelJackson if the question is about something in the inner confines of theology, then it might be a better fit there. If it's a question about how incest works as an ethical restriction, then it's not really about "how many descendants are required ...". Instead, it's about how moral rules can vary from culture to culture, which would be a good and interesting question. – virmaior May 19 '15 at 10:42
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    One does not need to worry about whether Adam and Eve are historical figures, pretty simple arithmetic shows that there are couples that share common parentage not all that long ago. – James Kingsbery May 19 '15 at 18:35

How incest as a taboo is defined is dependent upon the culture you are raised in. If I remember correctly, Cleopatra was the result of 27 generations of brother-sister marriages. In some cultures marrying your first cousin is ok, in others, second cousins are ok. In some to marry an uncle is ok. In others, several generations. Every society defines it differently. Why there are rules in the first place has never been settled. Some have held that it was a 'natural' mechanism for not allowing a particular weak DNA characteristic to become predominant. Others have said it is mainly a cultural taboo, that allowing relations between family members would not allow for stable family relationships needed by all societies to develop culturally.

Most of the taboos that are around were first developed when people were living in small to medium sized communities/tribes/villages of 100-200 people. Most pairings would take place within the small community as most people never had any contact outside their own communities during their entire lives. Having family taboos for pairings allowed inter-family bonds to be established which strengthened the community as a whole and at the same time allowed individual families to be stable family units without sexual competitions within an individual family.

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