y'all have to realize that different societys have a different definition of incest

in almost all societies, parent/child relationships are a nono.

sister/brother relationships are generally frowned upon, although not unheard of- especially in cultural mythology (not just greek and roman)

when one goes to cousins it gets more complicated- in a lot of societies, it depended on which side of the family they were on. in a matriarical society, cousins on the mothers side were off limits, while cousins on the fathers side were fair game, and frequently it was even encouraged...in a patriarical society, the opposite was true... and it has only been a recent thing that first cousins are considered off limits, after we began understanding genetics... before that, it was common to see first cousins marry, because of the stagnat populations...not a lot of people moved around, so their choice of mate was the people they grew up around, generally family- also,, there was the desire to keep money and land in the family

the smaller and more isolated a population, the more likely the people are to have a system of acceptable cousin marriages, etc...