Appreciation of beautiful things is built into our genetics.

Attraction to good looking people is a very natural thing, because good looks = good genes, and our bodies tell us that *ahem*-ing with people with good genes = better chance at their children turning out to be good looking as well, therefore better chance of them passing down their genes.

There's alot of scientific studies on this subject, where they found that even babies preferred to look at beautiful people.

Of course, there are other factors that contribute to this. Nowadays people lead less active lifestyles and as a result become fat. Societal preferences today are that people who are fit, are more attractive than fat people, because it implies that they have time (or have a strong discipline to make time) and can afford to keep themselves in shape.

It also shows a strong dedication to persevere in accomplishing a goal, and simply keeping fit requires changing one's lifestyle completely, which means sacrificing the leisurely lifestyle of being a couch potato.

Its a complete reversal of ancient times where fat people were regarded as beautiful, as only rich people could afford to relax and eat all they want, but peasants could not.

Still, members of the opposite sex will generally appreciate and be attracted to people who make a strong effort to improve and maintain their physical appearance.

For example, if you compare a guy who goes about in public dressed smartly and has taken care of his personal hygene and appearance; with a similar guy who goes about in slippers, singlet and shorts who reeks of BO and hair that hasn't been washed in weeks... i'm sure you'll agree that the former is far more attractive than the latter. The same goes for female equivalent.