My opinion
... not speaking for the others... There are varied opinions on this subject...from those more learned...
Genesis 1:26 Then God said, “Let us make human beings[
b] in our image, to be like us. They will reign over the fish in the sea, the birds in the sky, the livestock, all the wild animals on the earth, and the small animals that scurry along the ground.”
27 So God created human beings[
c] in his own image.
In the image of God he created them;
male and female he created them.
Genesis 2
Then the Lord God formed the man from the dust of the ground.
He breathed the breath of life into the man’s nostrils, and the man became a living person.
8 Then the Lord God planted a garden in Eden in the east, and there he placed the man he had made. 9 The Lord God made all sorts of trees grow up from the ground—trees that were beautiful and that produced delicious fruit. In the middle of the garden he placed the tree of life and the tree of the knowledge of good and evil.
I believe Chapter 1 is speaking of the creation of mankind in general...
Chapter 2 speaks specifically of only 1 man Adam who God says, He placed Adam in a specific location, Eden, and personally breathed HIs life into Adams nostrils...
This is mentioned again in the New Testament, after the resurrection of Christ were it says He breathed on His Apostles and said, Recieve the Holy Spirit...
Incest, I don't think there was any ...
13 Cain replied to the Lord, “My punishment[
d] is too great for me to bear! 14 You have banished me from the land and from your presence; you have made me a homeless wanderer.
Anyone who finds me will kill me!”
15 The Lord replied, “No, for I will give a sevenfold punishment to
anyone who kills you.” Then the Lord put a mark on Cain to warn
anyone who might try to kill him. 16 So Cain left the Lord’s presence and settled in the land of Nod,[
e] east of Eden.
The Descendants of Cain
17 Cain had sexual relations with his wife, and she became pregnant and gave birth to Enoch. Then Cain founded a city, which he named Enoch, after his son. 18
This theory answers
whose Cain wife was and those who Cain was fearful would kill him...Since from Adam and Eve scripture reports at that time there were only 3 ... Adam, Eve and Cain...
However, if there were other humans in the world already, Cain could also build his city Enoch...