Science doesn't do "proof". It identifies the theories which best support all available evidence. Then tries it's damnedest to prove those new theories wrong.

Since the theory of evolution manages to be compatible with every scientific observation ever made, not to mention the fact that its principles are used to design vaccines, it has come as close to proof as any scientific theory can. The day evolution is proven wrong is the day I'll go back and check on gravity and atomic theory, too. They're all on equal footing at this point.

Maths is the only branch of science that offers 100% proof of its arguments. Evolution while backed up by a massive amount of evidence could never be proved beyond all doubt as there is always the chance that evidence has been misinterpreted. People used to believe that the world was flat and look what happened to that idea!

Ok so science has come a long way since then but we still have huge bias in the fossil record and gaps in our knowledge that will probably never be filled. We will never be completely sure.