Blavatsky's account of evolution, like those of her successors, is anthropocentric, pertaining to the evolution of man, not of the Earth. But it is an evolution extended out through cycles of cosmic evolution, into the cosmos, so it is not just an anthropology, but a cosmology as well. She speaks of human evolution in terms of a number of Root-Races, each of which existed for a while before being replaced by the next. The early Root-Races were not even physical at all, but vast, amorphous, etheric beings.
"The First Root-Race, i.e. the first "men" on earth (irrespective of form) were the progeny of the "celestial men"...in Indian philosophy the "Lunar Ancestors" or the Pitris, of which there are seven classes or Hierarchies" [p.74]
Unlike Judeo-Christianity, in Blavatsky's cosmology, "man" is the creation of higher spiritual hierarchies, but not of "God". They are described as the astral Shadows of the Progenitors [p.181, 188], "so ethereal and so little human in constitution they could not be affected by any elements - flood or fire" [p.181].
Just as the Polarians are themselves non-physical, so was the "continent" upon which they dwelled. It is referred to as the "Imperishable Sacred Land", which did not "share the fate of the other continents" [p.152] (i.e. to be destroyed at the end of the era).
The Polarians reproduced through fission, as the amoeba does today [p.189]. They "were devoid of all understanding (mind, intelligence, and will)." [p.188]. They were "ethereal, a-sexual, and even devoid...of desire" [p.176]. The individuals of this Race did not actually die. Instead, they "melted gradually away, becoming absorbed in the bodies of their own "sweat-born" progeny (the Second Race), more solid than their own." [p.179].
Blavatsky's thesis that our distant progenitors were gigantic etheric amoebas may seem incredible at first, but support comes from a rather unexpected quarter: a UFO researcher, Trevor James Constable, who photographed unusual UFO phenomena using infra-red film in an otherwise ordinary camera.
Blavatsky's Polarian Root Race, and even the term "Polarian", was adopted with little modification by Rudolph Steiner