Biological evolution is the process by which the genetic composition of populations of organisms changes over time. Answers may vary but should include something about isolation, adaptive radiation, and competition. Definitions in text.
All organisms are genetically different from all other organisms.
Only inherited traits are passed along. Traits leading to the greater survival of the species. Change is an ongoing process, still continuing even in the most highly evolved species. Answers may vary but should probably include the possibility that the original birds could fly but over time lost the ability to fly and this loss did not decrease their reproductive or survival capacity. At that time being flightless was neither an advantage nor a disadvantage.