Some background information: in this world there are races that are ageless. Meaning they stop aging at what humans consider age 30. This of course means that both men and women remain fertile, essentially indefinitely. This could mean that your great-great-great-great-grandfather could theoretically have a child with your great-great-great-granddaughter, if you aren't keeping track.
But that raises the question: outside of three to four generations, and anything outside third or fourth cousins, should one keep track of blood relations?
I am well aware of inbreeding depression, so naturally siblings and first cousins should be discouraged from producing the next generation. But with so many generations between them, blood relations so distant, is keeping track worth the effort?