This particular diagram takes a stab at showing how evolution itself follows octaves of development. That is to say, there is a definite scale of vibration that applies to the complexity of organisms.
Although this may seem like a reach to the reader, Gurdjieff made clear indications of this in his explanation of the ray of creation and the function of the octave in the development of organisms:
“Like everything in nature the human body which represents a certain whole bears both within and without the same correlations. According to the number of the notes of the octave and its ‘intervals,’ the human body has nine basic measurements expressed by the numbers of a definite measure. In individuals these numbers of course differ widely but within certain definite limits. These nine basic measurements, giving a full octave of the first order, by combining in a certain definite way pass into measurements of subordinate octaves, which give rise in their turn to other subordinate octaves, and so on. In this way it is possible to obtain the measurements of any member or any part of the human body as they are all in a definite relationship to one another.”
Excerpt taken from In Search of the Miraculous by P. D. Ouspensky, pub. Paul H. Crompton Ltd, 2004, p 135.
Given his unambiguous indication that the law of octaves determines absolutely everything, the complexity of organisms must of necessity proceed according to this law, with clearly discernible divisions, and in fact we do see such a hierarchy, which biologists have argued over for generations without resolving. The point is that the hierarchy follows a specific set of laws.
While this diagram should not be considered as set in stone, it gives us a rough idea of how these things proceed. One should note that it will take biologists many years of study to truly understand these principles, and no such study of any kind has been undertaken yet.