These always escalate really quickly. Creationist and evolutionist. We have a hard time grasping a truth that can't be presented in front of us in the form of an experiment. Maybe that says a lot about our society. That as a whole we bicker trying to strangle ideas and truths out of thin air, and that at least in some sense empirical evidnce is respected.
Let's take a look at a few ideas ( and keep in mind they are just ideas ) , and hopefully answer the original posters question, because it is a good and valid question!
Evolution is the law of our universe. I'm not speaking only biologically, but as a whole physical process. What is in this moment, is only because of what happened in the moment before. What processes and physical states where not able to survive in their structure ceased to exist and what remains continues on until it is unable to exist further.
You could also say, "An object in motion,tends to stay in motion until it is acted upon by an outside force." - Isaac Newton of course.
Now you can go up a step out of the realm of ideas, and see this reflected in the nature of stars and planets. Take Earth for example. Its traits such as its size, location, and movement through the cosmos, allows it to exist for an extended period of time, whereas a possible planet without those traits, may well be pummeled into oblivion, and perhaps was before it could realize its conception.
Now thats all fine and dandy until life gets involved.
Creationism
First we have a creationist standpoint, We were created by intelligent design. This could be any design, from god, from alien, or something beyond our understanding. Now Given current evidence there is no reason to believe we did not evolve from a lower species; however, we tend to allocate to much faith in our science. Given the basis that scientific facts are only tests that have been repeated succsesfuly a multitude of times, and the human factor of incompetence in the face of testing their beliefs, it is not improbable that it is in error. Though I suppose the same could be said of any science. I think the supporting factor in this belief lies in variables. One does not account for unknown unknowns in science for obvious reasons, though they may exist right in front of our eyes, changing the nature of things before us.
Biological evolution
Simple enough to explain, creatures reproduce, combining traits. The traits that are better survive ( most of the time ) and the ones that do not cease to be (most of the time ). This process takes millions of years to produce a new species, why then have we not observed this even slightly in man?
It could be that gaining intelligence and self awareness has somehow stunted the process. With our great control over the forces of nature, we can have great control over who lives and who dies, survival of the fittest is only observed in smaller scales now. However being the social creatures we are, a few different kinds of evolution have emerged.
Social evolution.
One society with certain traits coexists with another society. Much like the animals and microorganisms of the past, societies can split, reproduce, die, hunt, etc. they can produce the traits of a man on a large scale. When one society is in conflict (disassociate conflict as a negative term here) with another society, the inevitable result is a clashing of traits, and a reproduction of a new ideal, perhaps passed on from before, or entirely new. While this represents no biological basis, I think it still applies.
Technological evolution.
As science grows ever more prominent in our society, and at such a fast rate, I think that a technological evolution is in the near future. Where as normal evolution takes many years to come to fruition, a technological evolution would only multiply in speed with population increases, and scientific progress. With the ability to change DNA traits, splice genes, ascend to a computer based "pure energy" existence, body modifications, etc. evolution would be inevitable. Weather your creationist or evolutionist, you can't deny that.
You would even have those who would deny the technological evolution, thus creating two distinctly different races of a sort, So in this case, a divergent evolution would be at hand.
I have a more metaphysical idea if anyone wants to hear that ha ha.
I didn't mean to type so much, I usually don't do text walls, but take it for what you will, these are ideas, and I'm always open to having them smashed before me.....thus evolving my own mind!