No it isn't. Just because two species have similar DNA does not mean they share a common ancestor. Amazingly enough something so totally obvious and simple has not been overlooked by scientists.
Common ancestory is based on solid evidence such as the nested heirarchy of life, shared DNA errors, vestigal structures, and of course the fossil record.
Oooh, now there's some solid science! Not! The "nested heirarchy of life"? Tell me: Precisely how is information is added to the genome in the natural selection/mutation process that would allow for new body parts, new phyla, etc.? Where does the information come from?