What makes something a Pokémon when it ordinarily wouldn't be?

Why can I catch a Pikachu but not an ordinary mouse?

Why can I catch a Houndoom but not an ordinary dog? And how and why are there even dogs that breathe fire?

Mew is said to be the ancestor of all Pokémon. But if what makes a Pokémon a Pokémon is that it has powers and can be caught, then wouldn't Silph Co. be the ones to decide what the ancestor of all Pokémon is? If they wanted to include Darwinian siblings of Mew, they could have invented Pokéballs that could contain the beings one level of ancestry farther. Such as cats, presumably, since Mew looks like one. Is it just that Mew was the first animal with supernatural powers that was ever discovered by a civilization sufficiently advanced to classify and control it (i.e. Kanto)? Or were Pokéballs invented for more common Pokémon, and when Mew was discovered, it was declared the ancestor of all Pokémon because it happened to be the most ancestral being that could be captured in a Pokéball as the technology was formulated at the time, where its own ancestors and sibling species couldn't?

There are seven (?) world-famous researchers studying Pokémon. Why have none of them tackled this question that seems to be fundamental to the study? They all just seem interested in cataloguing discovered species and details thereof. Isn't this what professors are supposed to do: get in there and answer the big questions?

Speaking of which, if they do research for a living and aren't professionally involved in educating the youth, what makes them professors and not doctors?

Thoughts, /vp/?