An Ecology of the Planes

The Ecology of the Planes was a 14 century book written by the Cormyrean scholar Garth of Suzail. It discussed (at least in part) theories regarding the appearance of numerous species across the myriad planes of existence.

Content
The book shared the concept of 'diffusion theory' as an explanation why different species could appear across numerous, far-removed planes of existence, yet continue to appear near-identical to each other from a biological standpoint. The theory proposed that each species of creature arose from a single location and were each transferred to other locations across the multiverse. Each species' diaspora could be reasoned by multiple explanations, including randomly appearing portals, purposeful crossbreeding by plane-faring intelligent species, accidental escape, or by divine intervention.

A more radical iteration of the theory postulated that all in the multiverse originated from one single plane of existence.

According to Garth, one of the strongest confirmations of 'diffusion theory' were the many appearances of similarly-appearance dragons across the places, specifically those of chromatic and metallic species. It was said that each draconic archetype―namely Tiamat and Bahamut―each held a series of characteristics that were shared by each of the species that descended from them. Gem dragons were said by the author to be among the "fringe species", though they had their own progenitor, Sardior.

The topic of proving 'diffusion theory' through the examination of fossilization was introduced, but was believed by the author to only yield inconclusive results. There were too many planes in which fossil records were incomplete or otherwise unreliable.

History
Ecology of the Planes was published int he.