Colony Ship and Transport Capacities

Suspend your disbelief - Its just a game!

It's a game mechanic.

Starting at a "realistic" amount (say 1 million) would require either a complex micromanaged "migration" system, where you had to set up regular shuttling of transports from the big worlds to the colonies, or you'd have to wait an INCREDIBLE amount of time to get any decent population.

I.e. let's say each turn in 1 month, which is relatively in-line with the rest of the game's time usage. At 10% growth rate per month (far, far in excess of what is realistic), getting 1 million population to 1 billion takes 72 turns (6 years).  Using a shuttle system where each transport could only handle that 1 million people, you'd need 1000 trips to get them to 1 billion population. Given each trip takes > 1 turn, that's 100+ turns for a group of 10 transports.

Given that Production = Population in Billions, are you really ready to have a world that can't build anything substantial for 100 turns?

Sometimes, realism has to take a back seat to game play. This isn't a simulator, after all.

(plus, who's to say that they're not simply storing the DNA - a la The Titan from Titan A.E. - and then "hatching" everyone through some sort of artificial womb technology or the like.  Maybe they don't have to cart around 1 billion actual bodies.)

Except if it is DNA, than population wouldn't go down on the original planet, would it?

Unless the whole "population" count is a count of the number of DNA pieces available on any given planet??

Essentially what you're suggesting is there could theoretically be 2.5billion DNA pieces (how big do these pieces need to be? How long do they last? Skin flakes, hairs, etc ) from a man named Colin going to that new Colony.

So the new Colony is getting Colinized.

I don't disagree with the sentiments, but there is likely no perfect solution. Your best way to rationalize it is that they put people into cold-sleep containers, and these ships really are very very large, but made out of hardened butter and cheap as dirt compared to a proper military ship.

It also justifies how anomalies are sometimes colony ships filled with people ready to go.

It would be neat to see a 4X game one day, where basically the populations of your colonies NEVER rivals your homeworld, the Homeworld constantly represents the jewel of the empire, and your colonies barely contribute in terms of revenue, but provide raw material your homeworld has mostly consumed/used up. It would need to be a game with a tighter timeline/focus but it would be cool to see.

There could even be entirely different buildings/upgrade mechanics for the homeworld VS the colonies.