Oh look, mixing leads to higher IQ, which unlike behavior, is mostly genetic, not socialized. Mixed genes are fine.http://www.dailymail.co.uk/sciencetech/article-3146070/Mixed-race-relationships-making-taller-smarter-Children-born-genetically-diverse-parents-intelligent-ancestors.html …
It's not quite about that, but yes, inbreeding is generally a bad idea. Here's the real study. http://www.nature.com/nature/journal/v523/n7561/full/nature14618.html …