Has the definition of beauty changed?
I think what we perceive of as being attractive day to day has changed. We had voluptuous women being painted by Rubens 200 years ago. Today, of course, we've got Twiggy and really thin models walking up runways looking like coat hangers, but the basics of beauty have not changed. The things we value the most -- the quality and texture of skin -- generally reflects your health.
Of course there are times in our history when that's varied. You know there was the time when having had some type of pockmark meant that you weren't going to get smallpox, and therefore you were safe from further infection, and those skin lesions were seen as beautiful. And there have been times when being heavy was an important characteristic of your body shape because it meant that you were healthy enough to bear kids. But it all comes back to that the same fundamental insight, which is symmetry and the golden ratio of 1.6 to 1. This ratio governs many of the key aspects of what beauty looks like. These are basic realities in nature, because it defines how cells reproduce normally. So all beauty is telling you is that you reproduce normally.