evolution - any change in a population's allele frequencies over time

Pretty simple, isn't it? It's hard to believe all the fuss that's been caused over such a simple concept. Of course the controversy isn't over the fact that some genes become more common in organisms over time (and others become less common), it is due to the inferred long range consequences of these changes. The real controversy is over the concept of common ancestry (that all life on earth is descended from a single species). These pages contain a little bit of the evidence for evolution.
 

Charles Darwin didn't invent the idea of evolution - that was around before he was born. He simply proposed a mechanism for evolution and provided evidence for evolution and the idea that many  widely divergent organisms shared common ancestry. The mechanism Darwin proposed to explain evolution was natural selection. Here are a list of the conditions Darwin thought were required for evolution by natural selection:

1. All organisms produce far more offspring than can survive to adulthood and reproduce. This means that many of those offspring will die without reproduction.
2. Organisms vary in many ways, and much of that variation is heritable - that is, variations that exist in the parents are passed on to the offspring.
3. Some of those heritable, variable traits affect an organism's fitness - its ability to survive to reproductive maturity.
4.(This is the kicker.) Those traits that increase an organism's fitness will tend to be passed on to the organism's offspring and to subsequent generations.

What Darwin realized was that this tendency of organisms to increase in fitness by the increase of certain traits would lead to divergences in the characteristics of the offspring. Eventually, as some groups of offspring adapted to slightly different environments (than other groups), speciation would occur. Hence, The Origin of Species.

Of course, Darwin didn't know beans about genetics - he only recognized heritable variations - he didn't have any idea of what was behind the heredity.  But now we know that heritable traits are ultimately controlled by genes. Which brings us back to our definition of evolution - any change in a population's allele frequencies over time.

Even if you reject evolution, do you see the logic of how populations will become different from each other over time if there is variability in fitness characteristics?