There is no guesswork in science, if there is, it would not be called science. If solid scientific evidence is not provided to confirm the theory, the theory is discarded or changed. There is SCIENTIFIC evidence that NO-ONE CAN DENY for Evolution, thus making it A SCIENTIFIC THEORY. IT IS A THEORY. THAT IS A FACT. THE FACT IS THAT EVOLUTION IS A SCIENTIFIC THEORY JUST LIKE ANY OTHER SCIENTIFIC THEORY BACKED BY SCIENTIFIC EVIDENCE.
You say the universe had a beginning, are you reffering to the big bang? You cannot say since if it had a beginning, there must have been a creator. THAT IS GUESSWORK. SCIENCE QUESTIONS THINGS... What if matter and energy are infinite and have always existed? Science is working to answer those questions. Since WE DONT KNOW SOMETHING, IT WOULD BE LOGICAL TO NOT jump and say it was god, we have to look for a scientificaly correct answer.