"Boys have a penis, girls have a vagina."

Josh looked at the list of rules and found a rule pertaining to the most basic aspect of human anatomy.

-Typical biological males have a penis and testicles, while typical biological females have a vulva and vagina. Only men can sire children, while women carry the gestation process.

And then he decided to change it.

-Men and women may both have either penis & testicles or vulva & vagina, but not both. Anyone with a penis can only sire a child, while anyone with a vagina can only carry out the gestation process.

Josh looked at what he'd written and felt mostly satisfied. But then realized a problem. A newborn baby's sex would be unidentifiable until they were much older. So he added to the rule:

-Parents may only produce children the same as them.
-A male with a penis with a male with a vagina will only produce male offspring together.

-A woman with a penis with a woman with a vagina will only produce female offspring together.

-A man with a penis with a woman with a vagina will only produce male offspring with a penis, or female offspring with a vagina.

-A woman with a penis with a man with a vagina will only produce male offspring with a vagina, or female offspring with a penis.

'There, that takes care of the randomness,' thought Josh, imagining the ridiculousness of the world he'd just thought up. He tapped 'save as old rule,' then decided to take a nap.