Two diverse species naturally breed an offspring, and selective preserves raver new traits in a given environment, (they evolve).
I hope this helps.=^⊃
We grow the vegetation and we get our oxygen from plants and vegetation.
B .How organisms could change .
we have been evolved through same root, during the process we get separated and develop new features to adjust in the surrounding atmosphere, that's why our genes are matching with fruit flies and others.