Why then, after 1 year of gameplay, with no population growth traits or modifiers is my civilization population 225 billion people? A full 7 times the expected size?

WITHOUT modifiers? THat's Kerazy?! Never played Beta so I don't have any experience with it.

Ya but by the sounds of it your max pop isnt that high.
Which in the long run will make more money.
Also its needed for defence of a planet and making troop transports. I have succesfully replled 2 waves of troop transports with 1base that had a crap load of people on it.

u say u had a civ pop of 225B in one year? that cant be right...i dont hit 100B till mid-late game which i guess is roughly 3-5 years,wut concerns me about pop growth is the fact that only the comp torians seem to have a workign bonus, the thalans always have same pop as everyone adn when i play as thalan or torian i have the same pop or lower than everyoen else also even if i have the most planets or close to,but then the comp torian has dbl the pop no matter wut the game situation is...sumthin seems off about the pop growth buisness but i got no clue lol, ppl with thoughts come and share them

P.S - I never play with more than "uncommon" for habitable planets.

My population just hit 500 billion and I'm just stating 2227. No racial modifiers, and I just built the aphrodisiac achievement. I think I may have gotten a couple +1% bonuses from exploring anomalies as my pop growth number reads 53%, including 50% for the aphrodisiac.

It just doesn;t feel right. And my taxes are crap. I make approximately 2500 per turn and spend all of it. Am upgrading to banks on most planets, but my taxation is crappy.

I try and keep morale at above 85%. How much of an impact does morale have on pop growth?

Alright, I did a bit of spreadsheet math here. (What can I say, I'm lazy) Without bonuses above and beyond what I'd expect out of having high moral, (+100% or +25%) I can't figure out how the population got so high so quickly.

Here's what we'd expect:
On normal moral, we have fCurrentPop = fLastWeekPop * 1.03;
On high moral (+100%), we have fCurrentPop = fLastWeekPop * (1.03 + (0.03 * 1.00) ); //effectively, pop growth = 1.06, double normal rate
On good moral, (+25%), we have fCurrentPop = fLastWeekPop * (1.03 + (0.03 * 0.25) ); //rounded to the hundredths place, this is pop growth = 1.04, or staying at true floating point, it's 1.0375

My spreadsheet, however, says that in order for growth the get past 225 from 5, we need a growth rate of 1.08 for the majority of the time... For an entire year at that growth rate, we get 273,530Million... If we take week 49's population of 201B, and reduce that down to the normal 1.03 growth, then we'll get 226.226B, much closer to your actual results.

So, if there are absolutely no bonuses, other than moral, then you're doing the impossible, and have likely found a bug.

Here's what the code should look like...
fCurrentPop = fLastWeekPop * (1.03 + (0.03 * fMoralBonus) + (0.03 * fOtherBonus) );
Of course, I don't like hard coding constants, 'cause there are modders out there that like to tweak settings. Instead, I'd choose to read the base growth rate from a file.

That would give me the following code:
fCurrentPop = fLastWeekPop * (1+ fPopRate + (fPopRate * fMoralBonus) + (fPopRate * fOtherBonus) );

Now, even with keeping in mind the bug that I suspect, I still started writing the bug in...

Here's what I think the bug is...
fCurrentPop = fLastWeekPop * (1.03 + (1.03 * fMoralBonus) + (1.03 * fOtherBonus) );
Instead of multiplying the bonus by 0.03, the bonus is multiplied by 1.03... giving us a total bonus of 2.06 on 100% moral, and a bonus of 1.355 on 75%+ moral.

Since a planet's population affects the moral, we'll probably see one week of 100% moral, followed by a couple of weeks of 75%+ moral before the planet gets too full to get the astronomical bonuses. Imagine every single taxpayer, male or female, having a kid, plus an extra 6% of the people coming out of the woodwork to pay taxes, each week that there is 100% moral. Every week, there'd also be a little more than a third of the population having a kid each week. That's one short gestation period.

Now, since I don't have 1.1B yet, I can't verify this bug myself... but here's how you can verify it.

Look at the population each week... If it doubles, then slows down to what would then be expected levels, then the code has an extra 1 where there should be a 0.