As new changes in the DNA sequence are constantly being generated in a population's gene pool (changing the population's allele frequencies), some of these changes will be beneficial and result in traits that allow adaptation and survival. Natural selection causes evolution of a species as these beneficial traits become more common within a population. Evolution can occur within a species without completely resulting in a new species. Therefore, evolution and speciation are not the same.
Sam has been a doctor for 50 years. Now semiretired he often thinks about how medicine has changed over his life time. When he was a new doctor antibiotics were given out when ever some one had any kind of infection. Sam remember that giving antibiotics for ear infections was the standard. However over the years this approach seemed less effective. It seemed that bacteria that were once easily eliminated by antibiotics were not effected any more. Soon doctors were limiting how often they prescribed antibiotics to keep the bacteria from adapting.
Was the bacteria changing or staying the same?