Masturbation is a big taboo in certain parts of our society. However, in contradiction to this, there is the point of view that states that our hands are so positioned that we have easy access to that particular function.

From a theological point of view, if God didn't want us to do it He would have created us with shorter arms. From an evolutionary point of view, one can say that we did have short arms and the reason they got longer is that over tens of thousands of years we kept stretching them till we could reach our genitals.

From a comedian's point of view, it wasn't the genitals we were trying to reach but the itch in our rear end.