As a species evolves away from maladaptive forms, there may be occasional reversions. A well-known example is the tail in humans. A very small percentage of humans are born with a tail. My question is this. The appendix is possibly a vestige of an era when human ancestors were able to digest cellulose. True or not, we might expect that a tiny percentage of humans would be born with the ability (to varying degrees) to metabolize cellulose. Does anyone know if this is the case? Are there any documented cases of people who could metabolize cellulose? Thank you.