Evolution isn't a theory. It's a verified fact. Evolution can and has been demonstrated in the lab repeatedly. All evolution is change in any given system (biological or not) over time in direct response to external forces. Speciation is a theory. We have yet to to find a verifiable and credible example of speciation (one species becoming another). Every time a researcher thought they found one after careful examination they found it to be misidentification or errors in their process. So far we have yet to see one species become another in the lab.