Christians do not marry their parents or siblings in modern America like Letitia James, Illhan Omar, and other leftists have done.
Adam and Eve had two SONS. No daughters were ever mentioned. God favored Abel over Cain, because Abel killed and burned some animal and Cain had no animals to sacrifice. God, being all knowing, knew that his favoritism would make Cain jealous and would kill Abel.
That meant that there would be no third generation unless Cain mated with a woman, and there was at that point only one woman available.
So the entire human race, due to "God's" crappy parenting, is descended from a Motherf*cker.
READ THE DAMN BOOK, you IJIT!