So what does the "firstborn effect" actually affect?

[cwykes]

Firstborn effect as I've seen it explained, says that, unless you do something to shake up the randomiser, your sim parents will always have a kid with personality A which is based on their personalities, but is not actually random.  Everytime you quit the game (not just the lot) and come back to play that family, the first baby in that playing session will also have personality A.   The second kid in any playing session will always have personality B which depends upon starting point A and is not random either.  If your Sims only have 1 kid, it doesn't matter, if they have 10, it matters a lot. Something like A ABC ABCD AB gives you far too many kids with identical personalities.  Makes them easy to handle if they are all the same, but the game is already easy enough...

I tell people the maxis randomiser always starts in the same place and that's why their Sim families have kids with identical personalities.  Then they ask me questions I can't answer .....

Is that why my family
- always has boys/girls?
- had 2 sets of twins in succession?
- always has kids who look alike?

I don't like not knowing the answers, even as I reply "Go get JM Pescado's awesome ffslotdebbugger and it will solve all your problems."  If this is all posted somewhere else, please tell me where so I can go read about it.  I've posted how I think it works as well so you can point and laugh if it's wront, but please explain it properly!  I've searched and found bits, but not a coherent story.   It would be really nice to have something in the war room about it.....

[J. M. Pescado]

Is that why my family
- always has boys/girls?
- had 2 sets of twins in succession?
- always has kids who look alike?

Firstborn effect only affects personalities. Tendency to constantly spawn boys or girls is apparently an related artifact of a poor random number generator, but unrelated to this. Same story with twins. Identical children tends to be caused by homogenous genetic pools in CAS sims, where if your sims spawn with dominant facial features and none of these clash, the outcome tends to always be the same as a result, because your kids inherit all the dominant features.

[Renatus]

The answer to the first two is 'probability'. When you have a percentage chance of something happening that percentage won't necessarily happen evenly over a course of time; it may happen all at once and then not happen again for a long time. So, if twins is a 10% chance (no idea, just pulling numbers out of the air here), a user may experience them with 9 births being normal, the tenth being twins, and so on, but they may experience 3 sets of twin births, twenty some odd normal births, a few more twins, etc. To get any further into it someone else will have to explain, learning about probability was a long ago memory.

The last is probably because their sims actually have very similar facial features - most people seem to stick keeping the facial variation of their sims to a few template. However, I've also noticed when doing the "make a baby" thing in CAS that oftentimes the resultant sim will more often resemble one of the parent sims than the other - it seems the facial feature genetics may come into play there, where one sim has more dominant features and the other only has one or two.

[cwykes]

Tendency to constantly spawn boys or girls is apparently an related artifact of a poor random number generator, but unrelated to this. Same story with twins.

Do you have a recommendation for jogging the randomiser?  Quitting to neighbourhood during pregnancy? Making CAS sims? Does thelotdebugger help with this even though it's unrelated?  Thanks!

Identical children tends to be caused by homogenous genetic pools in CAS sims, where if your sims spawn with dominant facial features and none of these clash, the outcome tends to always be the same as a result, because your kids inherit all the dominant features.

OK so that is working as intended - it is really random, it's just the parents are similar.

Thanks Renatus - I too studied probability a long time ago!

[J. M. Pescado]

=
Do you have a recommendation for jogging the randomiser?  Quitting to neighbourhood during pregnancy? Making CAS sims? Does thelotdebugger help with this even though it's unrelated?  Thanks!

This one can't really be jogged, you just gotta go with it.

[cwykes]

Thanks JM.  So the only thing to do is save during the pregnancy, quit without saving if you don't like the sex and keep quitting until you get a result you like.  If you keep getting boys or girls, quit for the day and hope for the best next time.

The odds of twins are 10% like Renatus said as far as I know.  If the pregnant Sim has a pregnancy modifier, the odds are higher, but I don't know how much higher.  I'd also like to know if that pregnancy modifier is a one birth only token.

[Mirelly]

Tendency to constantly spawn boys or girls is apparently an related artifact of a poor random number generator, but unrelated to this.

Just to take issue on small point. I believe the births gender ratio comes out moderately well. Especially in view of the fact that generating genuinely random numbers is not exactly easy. With most players experiencing relatively few birth (the numbers are never gonna be large enough for statistically significant numbers to emerge ... to prove the issue either way. Whether the imbalances that seem to appear are the result of bad programming (a possibility that seems both likely and likable) or else simply occur because that is what Maxis intended, the end is quite satisfying. I would feel seriously cheated if all my married couples produced one of each sex.

I have a family of 3 sisters. One has had 2 boys, another had a boy and two girls, the third had 2 girls by her first husband and 2 boys by the brother-in-law who sired the first two boys in this sentence. That's a generation of 5 males : 4 Females ... ya can't cut it closer than that without going down the route first proposed by King Solomon ... and yet one male sim has sired four male offspring.

[Regina]

And then there's always that coin toss chance thing.  You toss a coin and you have a 50/50 chance of it coming up heads or tails.  It's the same with the births.  The percentages are based on each birth rather than all the births in the game.

It's the same with twins.  Each pregnancy has a certain percentage of ending up with twins, rather than there being a certain chance for twins in your entire neighborhood, and this chance is going to be the same whether a sim has 1 pregnancy or 20.  Each time there's that particular chance of twins.

My sister-in-law had a sim who ended up having twins three times in a row with no hacks in her game.  That's just the way those kind of odds play.

[cwykes]

That's how probablility is supposed to work, the problem is that the Sims2 can't actually deliver random  JM says:

Tendency to constantly spawn boys or girls is apparently an related artifact of a poor random number generator, .... Same story with twins.

[Pegasys]

Well a Sim child recently had <cough> a very tragic pool accident, due to the fact that she appeared to be, in every way, a clone of her older sister! Prior to her birth I didn't fully understand the Firstborn Effect, but after she aged to child, every feature appearing exactly like her sister, I said no more Sim clones and finally reread a gazillion posts about this phenomenon - this is the second or third time it's happened to me. I understand the personality part being identical but her facial structure also appeared identical; I guess that must be because of dominant facial regions of her townie Dad. 

[cwhitney]

Is that why my family
- always has boys/girls?
- had 2 sets of twins in succession?
- always has kids who look alike?

Firstborn effect only affects personalities.  Identical children tends to be caused by homogenous genetic pools in CAS sims, where if your sims spawn with dominant facial features and none of these clash, the outcome tends to always be the same as a result, because your kids inherit all the dominant features.

That's very strange, because I had been getting a string of identical looking children (with identical personalities, across many families) until I found out about the firstborn effect from you, and once I started avoiding it by following your instructions, not only were the kids no longer identical personality-wise, they also stopped being identical looking.  Yes, the kids now look similar, but they aren't clones of one another, which had been the case previously.

[Renatus]

I think the facial genetics of the parents play a part in the lookalikes, although I just now remembered that one of my first families in the game had two sons that were born pretty far apart but did indeed seem like exact clones of each other. The younger grew into a child a day before the older one was to grow into a teen, and I could not tell them apart. They may have ended up looking different as adults, but I deleted that neighborhood before I found out. Perhaps the facial genetics do get sort of 'stuck', especially if one parent has a lot of dominant features and the other does not (I have one sim that I've checked though SimPE who only has one dominant feature).

[cwhitney]

I think the facial genetics of the parents play a part in the lookalikes, although I just now remembered that one of my first families in the game had two sons that were born pretty far apart but did indeed seem like exact clones of each other. The younger grew into a child a day before the older one was to grow into a teen, and I could not tell them apart. They may have ended up looking different as adults, but I deleted that neighborhood before I found out. Perhaps the facial genetics do get sort of 'stuck', especially if one parent has a lot of dominant features and the other does not (I have one sim that I've checked though SimPE who only has one dominant feature).

My experience suggested that all genetic code was similarly miswired to produce identical features, so that both appearance and personality was thus affected.

Here's an example:



These guys also have two sisters that appear to be no different save from the basic structural changes that occur when you change a male sim into a female sim.

[gethane]

damn, you should make a children of the corn story with those clones. I'm scared they are out to take over the world just looking at them!

[Renatus]

Oh wow. That's weird! I haven't had clones since way back when with the base game, but after seeing that I will make doubly sure to use the "Re-Randomize sim generator" function on the debugger when I'm about to have a birth. I neither need nor want clones!

[Pegasys]

Here's my example:



They also had the exact same personality.

One of them, um, slipped and fell into the pool...