Building Your Population
[Submitted by: Toebin ]
It is recommend that you build your population as early as you can, since even if you only have a handful of cities with 31 population in the capital, you'll be able to generate enough research and gold to win the Tech or Economic victory conditions.

At 31 population, each population will generate 1 Production and 8 Resources (Research/Gold), giving you 248 research per turn (without Libraries and Universities).