H. P. Blavatsky
Every organized thing in this world, visible as well as invisible, has an element appropriate to itself. The fish lives and breathes in the water; the plant consumes carbonic acid, which for animals and men produces death; some beings are fitted for rarefied strata of air, others exist only in the densest.
Life to some is dependent on sunlight, to others, upon darkness; and so the wise economy of nature adapts to each existing condition some living form. These analogies warrant the conclusion that, not only is there no unoccupied portion of universal nature, but also that for each thing that has life, special conditions are furnished, and being furnished, they are necessary. Now, assuming that there is an invisible side to the universe, the fixed habit of nature warrants the conclusion that this half is occupied, like the other half; and that each group of its occupants is supplied with the indispensable conditions of existence. It is as illogical to imagine that identical conditions are furnished to all, as it would be to maintain such a theory respecting the inhabitants of the domain of visible nature.
From “Elementals”, Lucifer, August 1893