Cosmology, physics, biology, etc

Physics

The world is flat, specifically an infinitely tall cylinder with a flat top. The sun and moon go around it. They are the same size and distance away and are always opposite each other. The sun (and probably also the moon) goes two surface-diameters down the side of the cylinder. Although it passes close to the side of the cylinder, it does not get very hot on the side of the cylinder because "gravity applies to celestial light in convenient amounts". The cylinder has a core of of indestructible celestum.

Polaris is a sphere that hovers over the North pole and goes up and down. It exudes cold and causes seasons. Stars are five-pointed stars on the shell of the universe (and also dead people, see Stars, magic, and other bullshit).

There is air everywhere inside the shell of the universe. Gravity needs air to get into somewhere.

Science generally

The universe has opinions about the natural order. The first few times something "unnatural" happens, it is much more difficult than it should be, but then the universe gets used to it and stops objecting. For example, the first few times someone tried to make vacuum, the containers crumpled even though they were as strong as containers that worked for that later.

Genetics

Genetics runs on quadruple helixes. At conception, the expected birthday (a year from conception) is encoded genetically, and if the actual birthday is more than a month off from that date in either direction, the baby is born soulless.

There are physically separate strands of genetic material for species (SSNA, 'Species Similarities Notation for being Alive') and for being a living biological being at all (FNA, 'Fundamental Notation for being Alive'). DNA ('Difference Notation for being Alive') just refers to the things that can vary between individuals of the same species.

There are genes for hair color and skin color and other things related to physical appearance, the seasonal encoding based on the conception date, and there's one for the birthday which forms when the soul attaches.

Other Biology

Local humans age at the same rate relative to their years as Earth humans do relative to ours. That is, a local sixty-four year-old looks the same age as an Earth sixty-four year old despite the disparity in year length (though that might be because the disparity is not actually that large).

The hearts of local humans are slightly differently located than Earth humans' hearts, and are more in the place usually more metaphorically associated with putting one's hand over their heart. Their respiratory systems are worse than those of Earth humans.

Allergies do not exist, though some forms of influenza are called that. Lactose intolerance does not exist. 

Mosquitoes do not exist and neither does malaria, though the name gets used for other kinds of "bad air" illnesses, including suffocation due to insufficient oxygen.

There is not an evolutionary fossil record. Evolution does exist on the scale of microorganisms and parasites, however.