Relevant translation:According to the official story, the Monster Ball as we know it today was developed in 1925 based on the experience of Professor Nishinomori of Tamamushi University.
Professor Nishinomori, who was already nearing retirement due to old age, gave the wrong dosage of medicine to a macaque monkey, causing it to become debilitated. Perhaps out of survival instinct, the monkey shrunk its body and slipped into the professor's reading glasses case. This led to the discovery of the instinct of Pokémon to shrink and hide in a small space when they are weak, which is common to all Pokémon, and the development of a capturing ball that takes advantage of this instinct. The storage function of the ball and the transfer of the ball containing the Pokémon are not functions of the ball itself, but are based on the Pokémon's instinct.
https://ja.wikipedia.org/wiki/%E3%83%A2%E3%83%B3%E3%82%B9%E3%82%BF%E3%83%BC%E3%83%9C%E3%83%BC%E3%83%AB
Friend sent me this image and then I immediately remembered this was posted to 4chan at some point. People told the guy who posted it that it was phased out lore before the anime even launched.
Guess it made a comeback, internationally. Now, I guess the idea is that this takes place in 1925+, or the date's been pushed back on this discovery.