What’s beauty? You know it when you see it, sure, but what is it? It turns out that beauty is an important evolutionary byproduct.

An organism needs to invest energy in being beautiful. You won’t see healthy skin on a sick animal, because maintaining a healthy coat is too ‘expensive’. A sick peacock isn’t as spectacular as a healthy one. Or a genetically damaged chimp isn’t going to have as symmetrical a face. As a result, most creatures evolved their definitions of beauty in a mate to match the displays of healthy creatures.

Human beings have adopted this signaling strategy with a vengeance. I know a woman who is going to spend more than $9,000 having her hair styled in 2009 (hey, that’s less than $200 a week). Entire industries are based on human beings spending time and money in order to manufacture temporary physical beauty.

Businesses build lobbies that they rarely use, giant atriums with big windows and lots of empty space. It’s a waste, it’s expensive and it’s beautiful. It’s beautiful because it’s expensive.

Stop for a minute and think about the relationship between expense and beauty.

Do you make something beautiful? It could be the way you write hand written letters or leave a little extra on the product, even if maybe it’s not so efficient. Sometimes efficiency is beautiful, but only when it took a lot of extra effort to get there. Ordinary products are almost never beautiful. Austere products might be, but only when real effort is expended to make them that way.

Even the most hard-hearted people are suckers for beauty. We treat people and products differently when we think they’re beautiful. The reason people and organizations have invested so much in beauty over the years is that beauty pays off.

A website that doesn’t cram ads into every single nook and cranny is more beautiful… it’s also more expensive to run in the short run. A salesperson who doesn’t squeeze you for every penny is more confident, earning more of your trust–that’s beautiful.

When everyone has it, it ceases to be beautiful. (Babies are beautiful because time takes their babyhood away so quickly… it’s a guaranteed temporary effect). Beauty is a signal, not just a physical state.