This evidence suggest that all three living creatures that are mentioned have a common ancestor, even though they have been split into different types of groups of living organism millions of years ago.
Science suggests that all of the living organisms on the planet have a common ancestor. Since we are talking about a common ancestor that lived few hundred million years ago, the living organisms split into different groups, and they do not resemble each other nowadays. The fruit fly is an insect, and the humans and mice are mammals, so they are into totally different groups, and it is easy to see by the genetic evidence that they are very distantly related, but the humans and mice are much more closely related because they belong to the same super family, and their connection is much more recent.
