I'm investigating this system for the Guide, so thought I'd share some of my preliminary findings here so you guys can decide what is/isn't a bug. The descendant system is quite simple, but has a mechanic you wouldn't necessarily expect it to rely so heavily upon: Traits in the Household. Most would just think simply if we have a family of 8 we will have a lot of Descendants. That is true in a nutshell, but you can have many more or many less based on Trait compositions in the household.
Some traits are positive influence, while others are negative. The sum of all trait scores for a single Sim determines the size of the Descendants' household, while there is some random chance of another outcome - 25% that you have an Elderly household in the Future with a childless Sim. There is a 15% chance of a Same-sex couple living there as well as a 25% chance of a Single-parent Household, which are outside the rest of these factors. Given I doubt Traits in the Household changed much, then this could explain why some people don't see the changes they'd expect out of Descendants. Maybe something significant has to change (bump to the next threshold or household worth) to get them to be randomized again.
I will ultimately use this list for the Guide but will post it here to help people make significant changes to their Household Sizes. Note that there are some Lifetime Rewards you can choose that affect your Household Trait score. Once your Sim has the LTR, it's effectively a Trait.
Household Sizes on Trait Score:
-3000: 0, -2000: 1, -1000: 2, -500: 3, 0: 4, 500: 5, 1000: 6, 2000: 7, 3000: 8
Examples: -2500 would result in 1 descendant, +250 would be 5 Descendants.
Trait Positive Scores:
Brave: +250
Charismatic: +250
Dramatic: +250
Family-Oriented: +1500
Flirty: +250
Friendly: +250
Great Kisser: +250
Hopeless Romantic: +500
Irresistible: +500
Lucky: +250
Nurturing: +1500
Party Animal: +250
Perceptive: +250
Social Butterfly: +500
Trait Negative Scores:
Absent Minded: -250
Childish: -250
Commitment Issues: -1500
Coward: -250
Daredevil: -250
Dislikes Children: -1000
Diva: -500
Grumpy: -500
Hot-Headed: -500
Inappropriate: -250
Insane: -250
Loner: -500
Mean-Spirited: -500
Shy: -250
Snob: -250
Socially Awkward: -250
Unflirty: -500
Unlucky: -500
Workaholic: -250
LTR Positive Scores:
Attractive: +500
Carefree: +250
Disciplined: +250
Engaging: +250
Excellent Groupie: +250
Eye Candy: +250
Fast Metabolism: +250
Fertility Treatment: +250
Jock Influence: +250
Master of Seduction: +500
My Best Friend: +250
No Jealousy: +250
Observant: +250
Raised by Wolves: +250
Young Again: -250
Hidden Traits:
Mummy: -3000
Simbot: -3000
Wished for Beauty: +250
Wished for Happiness: +250
Wished for Large Family: +2000
Wished for Long Life: +500
Gameplay Testing Results:
Made a Single Sim with Hotheaded, Meanspirited, Unlucky, Dislikes Children, and Commitment Issues for -4000. Upon arrival in the Future, no Descendants.
Added a Sim from town, because of cheating I had to travel back and forth. This Sim had traits to hit a high number, +4000. She had 8 Descendants as expected, while Carl Tester still had 0.
I then married the two Sims. Their Trait Scores were then combined, resulting in 5 Descendants (got it to the 0-500 range).
I wondered if we can have more. It is clearly on an individual Sim level, unless two Sims get married. I did not see the Time Continuum change for the initial Test Sim until he Married his wife.
I went back to the menu and reloaded the save before the quick marriage. Upon giving the original Sim positive score traits reaching over +4000, unmarried, he had 8
descendants living at precipice parkway, while Dahlia's decendants lived in another house on precipice parkway. There were 16 total Descendants, both on the same road.
Conclusion: Maybe there's a reason the future felt a bit sparsely populated to me. It is clear that the population rises with Descendants, and the more unmarried Sims with positive traits you have in your Household, the more Descendants will populate the future. I am not sure on a max, but theoretically under perfect conditions there could be 8 households with a total of 64 descendants with 8 unmarried adults with almost all the same traits.
Funds and Wealth Now, there is an entirely different effect from Traits that places a modifier on your household funds that will determine one of four roads they'll live on, gradually moving up to wealthier areas. If you have not crossed over one of the thresholds for worth (150k, 200k, 300k, 400k) then the street they live on will not change. It doesn't look like Home value matters as much as cash on hand. This is speculation on my part based on the game stating Use Active Household Home Lot Value = False.
Examples: Losers and Absent-minded Sims will have a -150% reduction in Funds, maybe they're losing it all the time. Childish -0.5, perhaps from overspending. They are added up to a final multiplier that could be positive or negative, resulting in more or less funds for the future family. So, just because your Sim is Absent-Minded doesn't mean they will necessarily be poor, they may also benefit from Frugal or other Traits that give a positive increase in the Funds multiplier, while their Funds may also be high enough to be Rich despite a lot of negative multipliers. Most of these make sense and I"ll go into detail on the Descendants Guide that I'll be making for the EP.