The ancient wisdom asserts that the original life forms are created in the astral plane. This should seem less radical and impossible than it did at the time of the writing of the Secret Doctrine. Today we can look at Kirlian photography that produces actual photographs of some portion of the astral plane. We can note the healing work of such professionals as Barbara Hand that deals extensively with this aspect of the world.
Blavatsky explains that "ancestral types" are developed on this astral plane and provide the starting point for physical evolution.
Those purely secondary causes of differentiation, grouped under the head of sexual selection, natural selection, climate, isolation, etc., etc., mislead the Western Evolutionist and offer no real explanation whatever of the "whence" of the "ancestral types" which served as the starting point for physical development. The truth is that the differentiating "causes" known to modern science only come into operation after the physicalization of the primeval animal root-types out of the astral. Darwinism only meets Evolution at its midway point-that is to say when astral evolution has given place to the play of the ordinary physical forces with which our present senses acquaint us. (SDii648)
One other passage of hers has always struck me as sounding particularly like a description of design work on the astral plane. (Also note her reference to the "designers" in the next quote.)
In the creation of new species, departing sometimes very widely from the Parent stock, as in the great variety of the genus Felis-like the lynx, the tiger, the cat, etc.-it is the "designers" who direct the new evolution by adding to, or depriving the species of certain appendages, either needed or becoming useless in the new environments. Thus, when we say that Nature provides for every animal and plant, whether large or small, we speak correctly. (SDii732)