Taking real world population growth figures into account, which is a
1.14% (2006 est.) for the world and peaks w/ Liberia w/ 4.91% (2006 est.)
https://www.cia.gov/cia/publications/factbook/fields/2002.html
http://en.wikipedia.org/wiki/Image:Population_growth_rate_world.PNG
Assuming a growth figure of 3% and 1.200 human brains (12 month times 100 illithid)
there would be a need population of 40.000 human to get a steady supply (400 humans per illithid).
The Dark Sun comparison below would even call for 120.000 humans to supply the 1.200 brains per year...
There was a discussion on the WotC Dark Sun Forum where they estimated the required slave population to provide 1000 sacrificial victims to the Dragon / ''Dragons levy''
Q.: ''I'm trying to think of the exact demographics of the city states and i am using the reference that Borys would ask for 1,000 slaves each year from each citystate.
This makes me think that due to Athas's high death rate and large slave population and made me begin to think. Exactly how many people would be in a citystate so that this high death rate and birthrate were able to atleast produce 1000 slaves for harvest every year.''
Reply: ''Since that time I noticed that on the quick reference card for Gulg, found in The Ivory Triangle, it states: Quote: Population: 13,500 (race: *snip* ... class: 34% slaves, 26% judaga soldiers, 7% templars, 5% hunter nobles, 16% freemen, 4% foreigners and visiting merchants, 8% miscellaneous).
Soooo...if that's the case, [...] math shows that the listed population couldn't at all support the levy, at least not without an outrageous population growth percentage; even at a high 1%, Gulg would have a slave population growth under 50/year, and no matter how high (and highly unlikely) you want to make that percentage you're never going to come anywhere near the 1000 slaves needed each year. --> Realistically speaking, you'd need a pool of at least 100,000 breeding individuals, per city state, per year, from which to draw a 1000-individual levy.''
Population & Demographics of City-States
http://boards1.wizards.com/showthread.php?t=780548