ere are three theories on the wife of Cain and here they are : 1) His wife was his sister, who was left unmentioned in the Bible.
2) His wife was the first woman in the garden, who was kicked out for not obeying Adam, and whose replacement was Eve. There are many variations of her name : Isis or Lilith are the main names surrounded by this lore. In some cultures the children of Lilith are known as Banshees.
3) His wife was a primate, or an ape. Hence, evolution.
And Onelm ... of course he would of had to marry his sister if you went by the Biblical story ... but incest wasn't banned until after Abraham was alive so it would of been considered okay ... and who was going to say anything to him ...
obviously the book haves many mistakes and The book is entirely man-made with no divine interference whatsoever.
and this account and many are all over Koran , Torah and Bible
Plus I want my religion debater of always muzzy to show his replies here cause its an interestin disscusion