Sounds improbable, but fun to speculate about. I believe that pupa are begotten by parthenogenesis. Wizards are the only Female entity I know of in The Hive, so they may spin a cocoon around their pupal thrall babies and wait. Then Thrall are groomed from there. I believe the Ascension of Hive is linear. Start at Thrall, work up three paths. One; Thrall<Acolyte<Wizard. Two; Thrall<Knight. Three; Thrall<Ogre. I feel it's a non-caste system, where with the right ritual you can become something great.