Hm, it just occurred to me an evolutionary conjecture. It's apparently a consensus that primitive clan-based societies dictated that the individual had to mate with someone from another clan (probably due to noticeable general health benefits of avoiding breeding inside the clan).
Mates from inside the clan were readily available, but forbidden. Mates from outside the clan were possibly difficult to reach, but were allowed and yielded healthier offspring. This was long enough ago to be embedded in our genes, and recent enough to not have been superseded by other attraction principles in the gene pool.
Bottom line, we live in a theoretically monogamous/family-based society, with polygamous/clan-based genes. It's flawed by "design". But there's not much we can do about the picture. Just the small picture...
in december, drinking horchata
i'd look psychotic in a balaclava