So far we have seen what evolution is according to biologists. Now, it is important to understand what evolution is not, notwithstanding misleading claims by creationists. For example, evolution is not a theory of the origin of life. This is for the simple reason that evolution deals with changes in living organisms induced by a combination of random (mutation) and non-random (natural selection) forces. By definition, before life originated there were no mutations, and therefore there was no variation; hence, natural selection could not possibly have acted. This means that the origin of life is a (rather tough) problem for physics and chemistry, not for evolutionary biology.
The problem of the origin of life may not be insoluble, but it is very difficult because there are no fossils to guide us (chemical pathways do not fossilize) and scientists still have a very rough idea of even under which conditions the process occurred.
However, the currently most promising avenue of research is based on complexity theory, a new discipline that has already made large contributions in mathematics and physics, and which deals with the property of some physical systems to self-organize, i.e., to spontaneously increase in complexity.
There is nothing magical or supernatural in self-organization, as can be readily observed every day. For example, scientists have studied the spontaneous formation of highly organized and complex convective cells in the upper earth atmosphere, which occurs if certain environmental conditions are manifested. It could be that life originated because of self-organization under the proper environmental conditions, something that will require some bright young scientist to demonstrate one of these days.