Why do humans judge others by looks?

I have always seemed to ask myself this question, but I have always wondered why. Why is it that humans judge others based off of looks rather than judging them by who they truly are as an intellectual? It baffles me as to how people can do it, rather than getting to know someone and then judging them. I myself am judged based solely off of my looks by many, and it disgusts me. Everyone is so quick to judge, yet, won't take the time to get to learn about how someone truly is by actually talking to them.

I'm sure it is a natural human instinct for survival, but in today's day in age, we don't need to worry about the survival of ourselves by the way people look, we're much more advanced now than we ever were before. So tell me, why is it that humans do this?