Impossible? No, but not very probable either. I am not an expert on human physiology, but I presume it is very complex, and doesn't lend itself to hobbyists making large breakthroughs. If tomorrow I read an article saying a biologist has solved P = NP, I would treat that with a lot of skepticism. It is possible that he gained enough expertise to do so, but given that some very smart people have been spending a good portion of the lives on this, I wouldn't consider it likely.