Individuals who have succumbed to a histiminilitic virus in the Land of Light. The Touched were banished to the dark side of the region near the Stargate, where they could live in a barbaric, Neanderthal-like way. Tuplo and other members of the "Untouched" had all lost loved ones to the ailment, but they did not believe there was any way to treat the condition.
SG-1's arrival to the world brought antihistamine vaccines that cured the entire population, allowing them to return to their families and lives in the Land of Light.
The Broca Divide - SG-1 arrives on a world where what appear to be two distinct races exist between a distinct barrier.