Native American story about Night and Day? Back in High School, we read this story in English Literature class that had a very similar vibe and story as Cain and Abel did. I believe these two siblings lived on a turtle and they fought each other which resulted in one of them being the “bad” sibling who became the night and the “good” other that became the day. I am not sure if they were both of the same sex, but I am faintly aware that they were boys. This story is most likely of Native American origin, since we were focusing on early American history that year.

This sounds very much like _The World on a Turtle's Back_ , an Iroquois creation story. Originally passed down orally, a version was written down by the Iroquois author David Cusick in _Sketches of the Ancient History of the Six Nations_ in 1827.

The story concerns two twins, one right-handed and the other left-handed who live on the back of a turtle. They quarrel and fight, and the right-handed twin eventually throws his brother off the turtle into the void. When he went home his grandmother called him a murderer, and in anger he killed her too. As the question states, the story is often compared with the "Cain and Abel" story of the Bible, although there are also considerable differences between the narratives. Many variants of the story exist. One of the more common types is available here, although comparing with Cusick's version reveals the large degree of variation between them.