Why Monkeys Remained Monkeys?

Why Monkeys Remained Monkeys? the reason in evolution there is tendency that the specie evolves as its desire is. For monkeys they seem to be perfectly happy in the jungle and forests to have such setting jumping from tree to tree playing and searching for fruits. So any evolution effect is that they became more adapt in jumping between trees as their limbs adaptation became better and better. For humans they followed different path and we are what we are today.