This whole post is just for fun -- here is an article about applying phi (Golden ratio) to human faces and esthetics of human beauty. http://www.goldennumber.net/face/ If you don't know much about Phi try:: http://en.wikipedia.org/wiki/Golden_ratio The authors constructed 1.6... x 1 rectangles superimposed on faces and then try to establish the relationship of perception of beauty to phi. Teeth and ears (Fibonacci spiral) are subjects as well. Is this far-fetched? Somewhat. Is it fun to think about? Yup. But remember - humans have a lot of hardwired templates in our brains, faces being one of them. ...Ever see a face or an animal in a cloud? There are no cloud-sized people up in the sky. So we are prone to make connections and "see" things that may not really be there. There is also an evolutionary reason for this "ability" to see things that are not there. It is all about our ancestors, some of whom became tiger chow. Type I error is a false positive error, Type II is a false negative. The ancestors who made lots of Type I errors in identifying predators passed on their genes. The ones who made Type II errors were more likely to end up as a meal. Why: It's 200000 years ago. You are out looking for food. You think you see a tiger face in the bush up ahead. If you walk a different route(Type I risk), you may have spent a small amount of extra time, if you continue toward the bush(Type II risk) you may get where you are going more quickly. Sooner or later the tiger will be behind the bush. So sooner or later the Type II choice has survival problems. Because the tiger really is there. Being eaten is detrimental to passing on your genes and keeping your family alive. Being five minutes late is orders of magnitude less detrimental.