Humans aren`t supposed to wear eyeglasses either. 
That is true, but do you know why they do? When mankind was young, nature get rid of the weak individuals by killing them as soon as possible. When you lost your eyesight, you can't hunt and you die without food. This would be great in our time also, because nature would kill all retarded, including you. In the ages of the cave mans, you would be dead already because you are too stupid to survive. There wouldn't be any of those notes which your mom left to you: "Remember, my son: inhale, blow out, inhale ..."