Just one taste:
Following the update, trainers will now earn a catch bonus when capturing more of a specific Pokemon type, so for example, capturing Abra multiple times will now increase your chances of encountering the rarer, evolved Kadabra.
If you are a Pokémon Go player, read the article and grab the update when it hits in your region.
Just to clarify: You don’t increase your changes of encountering rarer Pokémon. Instead you increase your chance of actually catching one. Encounters are equal for all players.