Realistic Genetics

What this does, in one line

It gives your Sims an actual genetic history.

What’s wrong with the genetics in the game?

The genetics in The Sims 4 aren’t completely random. Kids do inherit features from their parents, but the base game has no real dominant or recessive genes and a high random mutation rate, so children often drift away from the family they were born into.

The issue is that the game stops there.

It doesn’t remember what the parents inherited from their parents. There are no hidden genes being carried through the family, so traits can’t properly skip generations.

A Sim with brown eyes can’t carry blue eyes from their mother and later pass them to their own child. Once the blue eyes are no longer visible, they’re basically gone.

That’s what I wanted to fix.

How it works

When a baby is born, the mod looks at the actual family tree instead of only using the two parents.

Hair and eye color are passed down using dominant and recessive genetics. A Sim can carry a color without showing it, then pass it on to a later generation.

Skin tone works a little differently. It blends the parents’ tones, with some influence from further up the family, so children land in a natural range for their family rather than a random shade.

Facial features can also come from different relatives. A child might get their mom’s eyes, their dad’s mouth and their grandmother’s nose.

Nothing unnatural appears out of nowhere. If a trait shows up, it traces back to the family.

A trait can disappear for a generation and come back later because the Sim was still carrying it.

What gets passed down?

• Eye color
• Hair color
• Skin tone
• Eyes
• Nose
• Mouth
• Jaw and face shape
• Other facial features

Every feature is rolled separately, so siblings won’t all look the same.

One child might look mostly like their dad. Another might look more like their mom. Another might randomly look exactly like a grandparent.

The point isn’t to make every Sim look identical. It’s to make them look like they came from the same family.

See the difference

This is one baby, generated twice. On the left is the game’s version. On the right is the mod’s version, built from the family underneath. Look at the family, then look again.

The parents and grandparents the mod pulled from.

See it across a family

This is where the mod gets interesting.

You might notice a grandchild has the same nose as their grandmother. Two cousins might have the same eyes. A hair or eye color can disappear and then show up again a generation later.

The longer you play the family, the more you can actually see traits moving through it.

You can look at a Sim and tell where they came from.

What you’ll see in the game

When a baby is born, you’ll get a genetics report showing what they inherited and which side of the family it came from.

You can also open the genetics menu to see the family members the system used.

It’s basically a breakdown of how the Sim ended up looking the way they do.

Fixed in this update (Beta 2.9.77)

Two fixes from reports this week.

• Same-sex pregnancies use both parents again. Kids were only picking up genetics from the Sim who gave birth. Both parents count now.
• Townies and other households you aren’t playing stay alone. The mod was touching Sims outside your active household (hair changes on age-up and similar). It doesn’t do that anymore.

Earlier in this beta

Installing it

1. Download and unzip the file.
2. Put RealisticGenetics.ts4script in Documents › Electronic Arts › The Sims 4 › Mods. It’s the only file. There’s no .package. Don’t place it more than one folder deep.
3. Make sure Custom Content and Mods and Script Mods Allowed are turned on in your game settings.
4. Restart the game.

Using it

For new babies, you don’t have to do anything. The genetics system runs automatically when they’re born.

You can also use the tool with an existing multigenerational legacy. It scans up the family tree, captures the parents and grandparents it can find, and builds the genetics from there.

You do not need to start a new save.

Is it safe for my save?

It shouldn’t delete Sims, change relationships or rebuild your whole family.

That being said, it is still a beta, so please back up your save before testing it, especially if it’s a legacy you’ve been playing for years.

The system is doing a lot behind the scenes, and there may be weird family setups or mod conflicts I haven’t seen yet.

Compatibility & other Sims 4 mods

Realistic Genetics is a lightweight script modfor The Sims 4. It only runs when a baby is born or when you open its menu, so it sits happily alongside the mods most simmers already run, including MC Command Center (MCCC) and Create-a-Sim custom content like custom skins, eyes and hair.

New to Sims 4 mods, or looking for more to pair with it? These are the trusted communities simmers download from: ModTheSims, CurseForge and Nexus Mods. And if you want the full detail on how the base game handles inheritance and its random mutation rate, the Sims Wiki genetics page is worth a read.

Questions