They say opposites attract. The concept crops up all the time in our culture. Romeo and Juliet, Fry and Leela, that 80s song with the cartoon cat. Well I had a thought today:
Biologically speaking, it's better to be diverse. There's more chance to survive as a species with more chances for advantages. The same is true in other places, education, the stock market.
The idea of evolution is that what is advantages to a species survives while what is damaging is removed. So, logically it would follow that we would be attracted to diversity. It doesn't help a species to have two of the same people reproduce.
This would also explain the phrase "If you met yourself, you would hate yourself". It's not that your unlikable, it's that you would naturally be repelled by someone just like you.
I have no evidence, so this is a theory in the scientific sense.