The whole concept of "higher" and "lower" lifeforms is anthropocentric and therefore unscientific.
Good point, Frollein. After all, the humble earthworm is just as highly evolved as any human being. Nevertheless, we can speak of organisms which are less highly evolved, and those which are more highly evolved, in the sense of better adapted to their environment. For example, the first amphibians were not highly evolved - their legs were splayed and therefore energetically inefficient for locomotion on dry land, whereas their descendants evolved legs which are energetically more efficient. And so on. And the general trend over evolutionary time appears to favour encephalisation, which appears to allow the organism to adapt to its changing environment much more quickly and efficiently than by genetic adaptation by natural selection. It is in this restricted sense that we can (very loosely) talk about life evolving from 'lower' to 'higher' forms, in my opinion.
"Politics is the art of looking for trouble, finding it everywhere, diagnosing it incorrectly and applying the wrong remedies." - Marx (Groucho)