There are. Gut flora, whatever proto-germ gave us mitochondria, etc. Most won't be and new ones are unlikely to be very transmissible (because transmissibility

There are. Gut flora, whatever proto-germ gave us mitochondria, etc. Most won't be and new ones are unlikely to be very transmissible (because transmissibility would imply features that would immediately make it negative) not would it be very noticeable (hey doc, my joints feel better than they did yesterday).