If Poké Balls can catch pocket monsters, then they should be able to catch other animals in the Pokémon universe too. This line of logic seems reasonable, as even the standard Poké Ball has been used by Trainers for nearly three decades to catch Mewtwo and hold literal gods like Arceus. However, the seemingly magic ball may have limitations when it comes to non-Pokémon species.
Poké Balls can be found nearly everywhere in the world of Pokémon. Whether trainers find themselves in the Sinnoh region of Pokémon BDSP or elsewhere, they will find the aisles of Poké Marts lined with various types of Poké Balls mass-produced for adventurers. Even when players are short on cash, they are likely to find some stranded in the tall grass or in a cave.
The availability of Poké Balls makes it evident that the piece of technology is likely incapable of capturing non-Pokémon species. If children could simply waltz into a store and buy a device that could capture all creatures in the animal kingdom - which includes humans - then the Pokémon universe would be in absolute shambles. However, there are more functional, theory-based reasons behind why Poké Balls cannot capture non-Pokémon species.
Pokémon Can Possibly Turn Into Energy: Animals Can Not
The major reason why Poké Balls cannot catch non-Pokémon species has to do with the theory behind how Poké Balls really work. While the mystery behind what happens in a Poké Ball has not been unveiled, one theory postulates that Pokémon turn into energy when being stored away. This is how Pokémon can be put into PC systems and why larger, more powerful Pokémon do not require larger, more powerful Poké Balls.
However, this begs the question as to why animals cannot be stored as energy in Poké Balls. After all, the basis of nuclear energy is centered around the fact that mass can be transformed into energy, so a dog or cat should be able to do the same as their Pokémon counterparts. However, the relationship between energy and Pokémon seems to be dramatically different than it is for other living organisms. The ability to transform into energy appears to be an inherent property of pocket monsters. It would further explain how Mega Energy works in Pokémon, why certain types can dematerialize when using the moves Teleport or Return, and how they even have elemental powers in the first place. Thus, Poké Balls seem to rely on a Pokémon's ability to turn into energy rather than actually turning mass into energy themselves, meaning other animals could not be stored in them.
While this answer to whether Poké Balls can capture non-Pokémon species may be disappointing, it is actually relieving. After all, if a Poké Ball could turn any mass into energy, it could then destroy humans at the atomic level by storing them away. So trainers should be happy that the world of Pokémon does not contain children walking around with something close to a portable nuclear reactor in their pockets.
