Since I'm basing this game on the Walkabout world, there will be a few automatic cultures to which characters can belong...
"Scavengers" - those who pick up the pieces of the past to rebuild society
"Cultivators" - farmers who saw little change when civilisation fell
"Tribals" - people who have gone back to the old ways of hunting and gathering
"Nomads"* - pack wanderers who travel in convoys on the ancient highways
"Outlanders"* - those mutated by the dark energies and radiation under the cities.
"Sheltered"* - those who could afford to weather the dark times in luxury
Those cultures marked with asterisks are uncommon, a player needs to prove themselves before they can create a character from such a culture, and there should never be more of these uncommon character types than commons. That's something else that Elgardt has never really regulated, and there have been moments when everyone wants a character who is a unique and special snowflake without realising that if everyone is a unique and special snowflake, then no-one is really special.
There is a seventh culture in Walkabout, the "Skyborne" who took to zeppelins and balloons to float above the problems of the world. They might be added into the mix later.
Each culture is divided into a number of castes. So it makes sense to do the same here... Each culture gives a special ability to a character, and each caste gives them a special ability too. This gives characters a few basic degrees of differentiation rather than a single ability.
But in general, all of the characters are "human".
I'm thinking that starting characters will begin with three paths that contribute potential abilities; background culture, childhood, and starting occupation. Over the course of play, they might pick up new occupations, new cultures (from secret societies or affiliation with new groups), or other special paths that might come up during the course of play. I might pull across the System 4 experience mechanism for this.