Adam and Eve were not the first. There was a pre-Adamic race of darker skinned beings made of a different substance that Adam and Eve. Think of it as the 1st version but there was a flaw so a second version was made. In order to differentiate between the 2 versions, a different skin color was used.
Adam and Eve gave birth to their 1st son, Abel.
Later in the garden, Eve was raped by a pre-adamic creature posing as God and Cain was born. He had within him the serpent seed that was prevelent within the 1st version
It was Cain, son of the serpent, that became the 1st murderer.
After the expulsion from the garden, Adam and Eve became separated from each other for a long time (I believe about 100 years) During this time Adam had relations with some of the pre-adamic creatures, one of which was called Lilith.
After they reunited, Adam and Eve gave birth to another son named Seth.
Darkness of the serpent seed spread across the world at that time until the days of Noah. The flood was the attempt to cleanse the earth of the serpent seed. However that did not happen because of actions taken by Noah's son Ham.
Having been warned by God of the impending catastrophe, Noah succeeded in building the Ark, one of the greatest
engineering feats of all time. Weighing 36,750 tons, it was built entirely of wood. It was 450 feet long, 75 feet
wide, and 45 feet in depth. On this Ark, God commanded Noah to "take of every living thing of all flesh." Because
of the limited space on the Ark, there could be no possibility of further reproduction of these species during
their time aboard, and God commanded that no intercourse should take place. This commandment was violated by an
inhabitant of the Ark, Ham, the second son of Noah. Ham had intercourse with a preAdamite woman on the Ark, a dark
skinned person. Their offspring was a black son named Cush, who became the symbol of Ethiopia.
This is how the serpent seed continued to flourish till this day.
Sauce
Curse of Canaan
https://ia802703.us.archive.org/31/items/pdfy-hH7b-2yjyACdh8nO/The%20Curse%20Of%20Canaan%20%5BA%20Demonology%20Of%20History%5D.pdf
From the Nag Hammadi Library
(The Apocryphon of John - The Secret Revelation of John)
http://www.gnosis.org/naghamm/apocjn-meyer.html
The Reality of the Rulers
(The Hypostasis of the Archons)
http://www.gnosis.org/naghamm/Hypostas-Barnstone.html