Nick Jonas and Tentative Theory

The first thing you said reminds me of the "relation theories" of socionics, basically: the best and most productive relations are with the type who share the same functions you have, with a preference for the duality, two inverse types (example: NeTi/SiFe).
The 3 girls i had a crush with in my life were Fi/Te users. Quite funnily for the socionics duality i don't have a great attraction for my duals, the same on the contrary or at least it is not happen yet.
Personally, i find that theory exaggeratedly deterministic, but if you want to deepen the theory here the page in wikisocion.
About the guy: i agree with ayoungspirt that he has Fe/Ti, for the moment i'm confused with the P functions, the shape of the eyebrows reminds to me more Ni than Si, so i'll return here later.

I thought about this theory before but I have not arrived to a conclusion. Personnally, if I recall my experience, I tended to be attracted to all kinds of types, but the ones who made an impression on me tend to be SeFis and NeTis. I dated once a JiNe though and a one I was attracted to was a SeTi or TeNi (they can look alike for some reasons). I remember a guy in middle school who I had an instant crush but I can't clearly recall his functions, I'm sure he uses Si/Ne and he seemed to be P-lead, I wouldn't surprised if he was SiTe but I think he was more a Ne-dom. Another guy that I found troubling was a SiFe, another one was a SeTi (not sure but quite likely). Hmm... I don't see much a pattern here... But i probably just like many kinds of people

Haha yeah. I don't think I believe that dual thing. Especially since my parents are each other's dual and they had a horrible relationship that ended badly. 

I think I maybe should have explained what I meant in a bit more depth. What Automatic Brain says, is that, when it comes to physical attraction, we as humans have an affinity for the familiar. The face shape, proportions and look that we find most attractive (on a purely looks basis) are those which are similar to our own or to those of people we are close to/love or feel safe around.

My very tentative theory is: Since the processes control what muscles one uses primarily in the face and body, it affects the static, purely looks based appearence of the person. We then might unconsciously find more attractive the looks derived from certain muscle contractions - brought on by different functions in different positions - in the face over others (in a purely look based situation). Or not

I also agree with Reckoner that it is most prevalent in the initial stage, before one gets to know the person. It's mostly about gut reactions.