The different stages or levels of technology are presented, by branch, in the Technology screen. You can see the technologies of all stages, but cannot research them until you have unlocked that stage within the branch. This is done by researching a certain number of technologies in the earlier stage:
Stage 1: Unlocked at game start
Stage 2: Unlocked after one technology from Stage 1 has been researched
Stage 3: Unlocked after two technologies from Stage 2 have been researched
Stage 4: Unlocked after three technologies from Stage 3 have been researched
Stage 5: Unlocked after four technologies from Stage 4 have been researched
However, the principle law of the Scientist political party, “Oracle of Science”, allows you to research technologies from one stage higher than what you have unlocked. The stages are unlocked independently for each branch.
Each time a stage is unlocked, you will automatically enter a competition with the other major factions that have unlocked that same technological stage. The first faction to successfully fulfill the requirements of the challenge will receive the reward (resources, bonus effects, a new type of Improvement, etc.). The other factions will not receive the reward or be able to complete the challenge. It’s winner-takes-all!