The concept of hereditary occupations existed from the time of the Shisei system, and even in the Ritsuryo system (a system of centralized government based upon the ritsuryo code), there were cases where families that had passed on techniques and knowledge down the generations had priority in obtaining technical official positions.
職業の世襲という概念は氏姓制度の時代から存在しており、律令制度に入ってからも何世代にもわたって技能・学術を継承してきた「世習」の家柄を優先して技術系の官職に就ける事例があった。