"He means that you are in a way his ancestors. Evolving is a gradual process, spread out over many generations where creatures change in form and shape. They can acquire different body parts, like thumbs or tails, or they can lose them.
" Stripetail could tell they were still confused. " He gestured and a orb appeared showing an image of a longneck. ' Let me try to show you what I mean. This is a adult longneck, like your grandparents Littlefoot, except its smaller and has a shorter neck. Now watch." The Longneck gradually grew in size, its neck and tail lengthened. Ali spoke. " That looks like an adult longneck so what?" " Ali, what happened was evolution. Over many many lifetimes, that longneck became bigger and longer."
Nick