It's a throwaway comment, but perhaps (as with most problems of philosophy) the problem is really semantic? What does "will" really mean, in free will? It imagines a little person sitting in my head piloting my body. It seems equally plausible that there is no central "me", I'm just a competing mess of programs running in my brain (at varying levels of abstraction), with the gut biome being the BIOS. There may be a hypervisor in there somewhere, but that's the most you can hope for in terms of rational direction. Everything runs in parallel, and the part I think of as "me" rationalizes decisions after the fact.

Horizontal gene transfer? A literal virus that changes who you are. It's interesting to think that by going paleo or vegan you can perhaps become another "person"...