Turns humans from a single race to a race with multiple subraces (most based on the environment their ancestors have lived in for generations).
Coastal Human - your basic viking or tropical sea-dwelling human
Demonblood Human - half-human, half-demon (my world does not have tieflings)
Desert Human - adapted to hot climates
Forest Human - from sub-arctic to tropical, forests are home to these people
Prairie Human - the most common type of human
Tundra Human - adapted to colder climates
Urban Human - generations of city living make for more "sociable" people