Compiled Explorer Tape Transcripts (Book) - from Robert Monroe

MIRANON: This applies to all levels of existence... physical or non-physical; it does not matter. As I have said to you earlier, plants exist en Level 1 to 7. They are on the vibra- tional rates 1 through 7. It is the same pattern. Animals exist on Levels 8 through 14. And when a person... or when a consciousness attains Level 14, it can no longer go any higher unless it is willing to change its form of conscious- ness. Levels 15 through 21 are what you call human life on this Earth. When a person progresses to Level 21, he then has the choice of going higher or staying within the realm of human form. But he cannot go higher unless he is willing to give up human form.