i feel i explained why it makes perfect sense in the OP.
Well, you didn't. It could just as easily be any Pokemon.
For instance; the first Pokemon appears. Let's say it's Bidoof. Bidoof splits into three different species; Pachirisu, Poliwag, and Nidoran.
Emolga, Pikachu and Plusle/Minun evolve from Pachirisu.
Feebas, Tynamo and Tirtouga evolve from Poliwag.
Aron, Scraggy and Sandshrew evolve from Nidoran.
And then each of those other Pokemon evolves into new species, and so on. No reason to select Pikachu as the precursor.
i selected pikachu, because like i said, there are pika clones in every gen, implying that pikachu is the original and most superior, thus it's offsprings didn't need to evolve much which is why they still look like the original pokemon ,pikachu.
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The game canon states that most of the non-Legendary Pokemon derived from Mew. Though either way it would be rather odd that ALL those Pokemon evolved from something that was already a multicelled, fully developed species. A species that apparently is still around (albeit in very small numbers).
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