According to a theory developed by Drs. Daniel Jackson and Robert Rothman, the Unas evolved on the same planet as the Goa'uld and were, therefore, the first hosts to the symbiotes. Eventually, however, the Goa'uld preferred to take human beings as hosts because their bodies were more easily maintained. Because of their physical strength, however, the Unas became slaves of the Goa'uld, primarily used to mine the precious mineral naquadah upon which the Goa'uld's technology depends.