Pokemon GO has had several varities of Pokemon in the Game. There are a total of 151 pokemon in the comics and they have not yet all been discovered. There are talks of certain pokemons being region locked. They will only be found in the regions which is their natural habitat. Naturally there has been a lot of speculation and confusion about the way these pokemons can be obtained.
One Pokemon GO player asked the same question :
@lady_maethoriel the eggs can only be found in their natural habitat.
— John Hanke (@johnhanke) September 22, 2016
As you can see certain Pokemons can only be found in their natural habitat. So good luck trying to trot the Globe to capture all the Pokemons! 😀