Exogamy often results in two individuals that are not closely genetically related marrying each other; that is, outbreeding as opposed to inbreeding. In moderation, this benefits the offspring as it reduces the risk of the offspring inheriting two copies of a defective gene. Increasing the genetic diversity of the offspring improves the chances of offspring reproducing, up until the fourth-cousin level of relatedness; however, reproduction between individuals on the fourth-cousin level of relatedness decreases evolutionarily fitness.
Does "outbreeding" or "inbreeding" benefit the offspring more?
"Outbreeding" is more beneficial to the offspring as it reduces the risk of inheriting defective genes, increasing the offspring's ability to reproduce.