The question that perplexes me - why does evolution progress from the simple to the complex? The simple bacteria and other "primitive" forms of live are by no means less "viable" then more complex forms -- animals and humans. Many of these "primitive" species remain the same for the hundreds of millions of years, survive perfectly in their enviroments and don't need to evolve into the complex forms. Indeed, complex forms are often more fragile and susceptible to the environment perturbations than primitive ones. So how natural selection alone can explain the general vector of evolution - from simple and primitive to more complex forms? Or could there exist some another force apart from the natural selection -- to "push" evolution in the direction of complexity, developed nervous system, self-awareness etc.???