So,
By digging in the work of [ORIENTATION] tag, i was surpised to discover that a full range of parameter did not apply to "non tracked population" during world gen, aka : "non historical figure".
This make large problem between worldgen behaviour of a race and its behaviour in game. Ans as we can have now (since tavern and co) a lot of other race in fort, it should be usefull to improve a bit this type of gap.
Example of a fail : make a race with 100% assexual men and female and show it spread like bunny during worldgen. Or observe simply the explosion of birth during worldgen while you have all the difficulties to make marriage in a fort in a same period of time (let's say 10 years).
My suggestion is that all parameters applied to races that limits the briths etc... should apply to populations, even non historical figure, during worldgen on simulated pops. And it should be relatively easy to implement as all these parameter are perfectly predictible.
For example : ORIENTATION tag which create assexual percent of the population, gay population, bissexual or heterosexual should result in only hetero and bi population being a part of the simulation for poping pops during world gen. (by simply substracting individual pops)
I don't know if the age is taken too, but if not, it should too.
Also, in fortress mod it seems that sharing gods helps for marriage, it should play a role too on race with a PANTHEON. It could be simulated costlessly through statistical estimation.
I didn't know the other parameters but i imagine this could be tracked too. ^^
An other way could be to let the player set a [ALL_HISTORICAL] tag that track all its populations despite the high processing charge. But both could be done : An improvement of the simulation and an avaibility of this tag.
That was my idead, sorry for bad english