http://wiki.cotch.net/index.php/Evolutionary_ladder
Evolution works by gradual slow mutation, not spontaneous leaps. Evolution is not a preset Pokemon-like path, it is a series of gambles with random mutations being favoured through natural selection. Even if you waited for a trillion years, ants will never evolve into shrews. Chimpanzees will never evolve into humans. And so on. In evolution, the only "ladder" is in better adaptation to your environment. There are no lower or higher animals.