They where born in Disney animation.
Disney animation started with the dream to tell stories using animation, it took some time for it to become the big animation company that we know and love now a days, they explored with various animation techniques and learn but, it wasn´t until the animators created a system with 12 rules that every animation should have, in order to look realistic enough, and those rules later became the 12 principles of animation and the animators that defined them became the nine old men.