In “The Wave In The Mind” Ursula Le Guin wrote about the different ways dogs and cats regard themselves. Dogs seem to be unaware of how they look, how big they are, the poses they strike, how we might see them. Cats are the opposite, with a highly tuned sense of appearance. She’s very funny about it.
Then she moves to how we regard ourselves and our notions of beauty: how it is a given that the young are beautiful, but how what she calls the “ the rules of beauty “ are manipulated to create ideals that people starve and abuse themselves to match up to. These rules, embodied by movie stars and models, change from time to time, and from place to place.
And then there is the beauty that comes from the confluence of body and spirit, a timeless beauty that is present at all ages, and yet somehow does not reflect in a mirror. It is a beauty that is expressed by artists, not by industry, and it lives for ever.
You can read more about Le Guin’s thoughts about beauty in this article http://www.brainpickings.org/2014/10/21/ursula-le-guin-dogs-cats-dancers-beauty/