There’s a debate on that?
…huh.
To be honest, I never knew it was in question. All the big fansites that I know of always capitalise them, as do the games themselves, the official website, and promotional materials. Frankly, I’m not sure I can think of any actual evidence that, in-universe, the names of Pokémon species are not capitalised. I suppose the easiest way to account for this is by saying that it’s simply a point of convention specific to the cultures of the Pokémon universe. They capitalise Pokémon names because they do. Rules of capitalisation are not universal by any stretch of the imagination – German, for instance, capitalises all nouns, while French doesn’t capitalise days of the week, months of the year, or nationalities (however, it does – I have just checked pokemon.com/fr – capitalise the names of Pokémon), and Japanese (like most languages that don’t use the Latin alphabet) has no equivalent to capitalisation at all, as far as I know.
(Also, purely as a point of incidental interest, by convention species names should not be capitalised; genus names should be – so humans, for instance, are Homo sapiens, capital H, minuscule s, chimpanzees are Pan troglodytes, capital P, minuscule t, and so on. Attempting to apply this distinction to Pokémon is probably a waste of time, though, since according to strict biological definitions most Pokémon are actually subspecies or breeds of only thirteen species)
