I hate to burst your bubble, but even the most die hard creationist does not deny evolution within a species - it is the supposed evolution between species (macro-evolution) that is the true controversy. The fact that there is variations within a species is no proof that it occurs between species.
It has been suggested based on fossil findings that a species exists on average for 5 million years. In that time enough mutations and environment changes can occur to lead to an organism being defined as a different species of the same family.