>>39796103Gen 1/2 seem to have been in a more realistic world where Pokemon were relatively limited in their spread and recently exploding.
Even eggs were a new discovery, many Pokemon were very rare, Starmie and Clefable are hinted to be from space, Grimer/Koffing etc are created from pollution, Ghastly is supernatural, etc.
The Pokedex makes reference to normal animals and some real locations like the USA and South America. Many of the gen II Pokemon are brand new, appearing only in Kanto despite just having adventured there a few years earlier. It carries over a bit to gen III, but by then they had commited more to the no more real world stuff.
My head canon (at least for the first two gens) is that Pokemon are originally from space, sort of like the Thing and gradually absorbing the dna of normal animals until it's a Pokemon world. The war and pollution mentioned in gen 1/2 are the catalyst for them exploding.
Their dna is extremely malleable/adaptable and by our scientific standards there are actually only roughly 15 species of Pokemon the "egg groups", with most legendaries being specially adapted and unable to evolve or produce "eggs". Furthermore the "egg" is not a conventional egg, but the base larval stage of a the species (potentially a budding form like a jellyfish) hence why the daycare people never know how they got there and Pokemon (especially female and amorphous groups) don't show any signs of pregnancy or gestation despite their wide variety of appearances.
Even people begin to show signs of becoming Poke-ified with psychic type trainers showing actual powers and the Pokedex claims one human boy evolved into a Kadabra.
Fossil mons went extinct or were limited because dinosaurs were strong enough to compete and of course the asteroid since it was mostly a real world setting.
