According to various evolutionary theories, living organisms change their physical and anatomical structure over time in order to better adapt to their changing environment.
Speciation is the product of evolution.
The evolution of life on earth does not entail the extinction of one species and the emergence of another; rather, it entails the emergence of new species through the adaptation of existing ones.
The new species may or may not be superior to the previous species. As a result, evolution should not necessarily be considered synonymous with progress.