Is Darwin's theory justified

Yes. There are numerous justifications both for and of Darwin's theory. It beautifully and simply explains the diversity of the tremendously complex biological world in which we find ourselves.

Darwin's theory of evolution boils down to just two simple rules. These are that replication is imperfect (variety is introduced into an organism's offspring), and survival is preferential (changing environmental conditions discourage replication of "less fit" individuals). These two rules can be further summarized as: Random mutation plus natural selection. RM+NS. Evolution is the heart surrounding these initials, carved deep into the bark of the tree of life.