Physical appearance is, of course, one of the very first things we notice about one another. A male bird's beautiful, brightly colored plumage intrigues prospective mates. The same is true of humans. I recently tried to persuade a good friend that charm and charisma were the things that men eventually and ultimately responded to in a woman. "The first thing we notice," he replied, without missing a beat, "is how she looks. If we don't think she's attractive, we never even get to the charm and charisma."
A study done in 1990 showed that women favored men with large eyes, prominent cheekbones, a large chin, and a big smile. The researchers who did the study said that these features indicated "sexual maturity and dominance." These characteristics are indicative of high levels of testosterone, which shapes the larger size and sharper contours of the male face. (Estrogen, on the other hand, is responsible for the round softness of women's faces and the extra fat in their cheeks and lips.) On some primal level, women found these very "masculine" facial characteristics attractive. Women were most attracted to men who seemed sociable, approachable, and of high social status. They also gave high marks to expensive or elegant clothing; apparently, it's not just birds who like beautiful plumage.
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Men, on the other hand, look for features that signify good health: regular features, a good complexion, and a good body. (It will perhaps interest you to learn that—as you dreaded in junior high school—while large breast size does influence sexual attractiveness, it does not carry a lot of weight in mate selection.)
Another interesting observation: People choose mates with physical characteristics similar to their own (hence couples really do look alike, as dogs resemble their owners).
Are we all just fundamental narcissists? I think it's more likely that after a lifetime of looking at ourselves in the mirror, our features and coloring seem "right" to us somehow. Maybe we choose the genetic material closest to our own, in an "If it ain't broke, don't fix it" paradigm.