This will mostly be things from my main fictional world, Ra'aknis, but there will also be some things from different worlds.
In our world, humans evolved from apes. In the world of Ra'aknis, humans evolved from mermaids.
Mermaids are aquatic mammals, closely related to seals and weasels. They have the same level of intelligence as humans, and have multiple cultures.
The evolution of mermaids to humans went faster than an aquatic creature becoming terrestrial would in our world. Rather than a few million years, this evolution took only 1 or 2 thousand years.
Humans specifically evolved from the population of mermaids living in a bay on the western continent. These mermaids lived closer to the coast and went onto land more often than other mermaid populations, which then lead to them re-evolving legs.
The first humans considered themselves to be the same as mermaids, and part of their culture. Humans and mermaids sang and ate together, and they both used the same sign language.
Soon, humans started developing their own culture, and their own sign language. They started augmenting their sign language with singing, and that singing turned into a spoken language of its own.
Humans started going further and further inland to hunt and gather. Some humans stayed by the bay, living as terrestrial mermaids, but most humans left to form their own culture. They roamed a territory along the Anis river, not far from the bay. They called themselves the Nisax.
It doesn't take long for humans to discover fire, and even less time for them to assign mythological significance to it.
The Nisax believe fire was gifted to them by the god of lightning. The legend goes that not long after the Nisax split from the mermaids, a young girl got the idea to try and make fire. She tried many things, failing every time, and so prayed to the god of lightning for help.
The god decided to take a small portion of his power and put it into a rock for the girl. But when he gave her the rock, it immediately burned her hand. Seeing that even a small portion of lightning power was too powerful in one stone, he split it into two, and placed them far away from each other.
The god told the girl that one stone would be near the river, and when struck against another rock, would chip into sharp points. The other stone would be found uphill from the river, would glitter the colour of the sun, and when struck against another rock, would release a foul odour.
So the girl found these rocks, flint and pyrite, and struck them together to make sparks. The Nisax believe these sparks to be the god's power turning into tiny bolts of lightning.
In another myth, this same girl makes small humanoid figures out of clay. One day, while playing with her muddy toys, she drops one into the fire. She wants to retrieve it, but an elder stops her, saying she will just have to accept this loss and move on.
When the fire has burned out, the girl goes to retrieve her ruined toy, only to find that the fire had made the clay stronger.
In certain parts of Ra'aknis, hair is considered to be very important and a part of the soul. People in these parts never cut their hair, except for in cases of illness.
When someone dies, their hair is cut off and burned. In some areas, all their body hair will also be shaved off and burned. The ashes are consumed by their community as a form of ritualistic cannibalism, and used as pigment for face paint used in the funeral ceremony.
The dead's lips are cut and their blood used to stain ceremonial clothing. Some areas save some hair from burning to embroider onto these clothes. The dead is then dressed in the clothes and buried.
Some areas, rather than cutting the lip for blood, will cut off some of the dead's genitals and use the blood from there. The cut-off genitals are boiled in water and the water drunk. The flesh itself is either divided into small pieces and consumed among the community, or wholly consumed by a parent, spouse, or child.
If the person died in a battle or from an injury, a few bones may be taken and boiled into broth, which is then eaten with the meat of a stag.