He evolved a new theory after many years of research - This started and ended some time in the past. You would also use simple past if you specified a time: "Two days ago, he evolved..." Present perfect is used to talk about something that happened at some unspecified time in the past. Also, it is used for something that is still affecting the present. "He has evolved..." would be used to talk about a recent development, or used in a list of his accomplishments if I am talking about his life up to now. One thing - if you are using specified time, you CAN'T use present perfect.

he has is correct , has means he did.

the first sentense emphasizes the result. the second one emphasize the procesure.

He evolved a new theory after many years of research. He has evolved a new theory after many years of research. The first one has broader use. The second one is a bit more narrow in terms of when you would use it. You may use it when introducing someone, for example at a business meeting or academic job talk: "He has published in the top academic journals." In terms of first-person, you'd also use it in such situations as in a job talk: "I have studied three languages and advanced statistics." It may express that something is expected to continue. For instance, if I say "I have published in top academic journals," I am likely inferring that I am going to continue to do so. I HAVE done it, and I will continue to do it. Whereas if someone said about me, "He published in top journals," that would probably be at a funeral or retirement ceremony: it is done, it is over. It will not happen anymore.

has is present tense without it the sentence is past tense (: