I am one, who believes God created only two, Adam and Eve. It fits better with the scriptures to me. Gen 3:20And Adam called his wife's name Eve; because she was the mother of all living.acts 17:26And hath made of one blood all nations of men for to dwell on all the face of the earth, and hath determined the times before appointed, and the bounds of their habitation; To me this is saying Eve is the mother of all and that there is one blood line for the nations of men. How old do you think Cain was when he killed Abel? Gen 4:3And in process of time it came to pass, that Cain brought of the fruit of the ground an offering unto the LORD.I think we can assume they were men, Cain was a farmer and Abel had his own flock. The bible is telling us that there was a process of time. So if Adam was 130 years old when Seth was born and Eve felt Seth was the seed in place of Abel whom Cain killed. We can assume these events are fairly close. (the death of Abel and the birth of Seth)If Adam waited till he was 20 years old to have Cain, which I am sure he didn't have to wait to have children, and after Abel was killed, he waited 40 years to have Seth. That would mean Cain could have been 70 or betterGen 5:3And Adam lived an hundred and thirty years, and begat [a son] in his own likeness, after his image; and called his name Seth:Gen 4:25And Adam knew his wife again; and she bare a son, and called his name Seth: For God, [said she], hath appointed me another seed instead of Abel, whom Cain slew. If Cain was any where near that age he probably already was married, when he killed his brother. By this time, there could have been many sisters, nieces cousins. The bible doesn't say he found a wife in the land of Nod it says he knew his wife and she conceived. It is only saying he and his wife had sexual relations and she became pregnant. Is telling us Cains wife conceived Enoch in Nod, not that he found his wife in NodAs far as marring a relative I don't think it was a sin at the time, I think it was acceptable for two reasons first, Adam and Eve were created perfect sin had not yet come into the world, so there would not have been any genetic flaws in there genes They would not have had to worry about physical deformities or metal issues Second Abraham married his half sisterGen 20:12And yet indeed [she is] my sister; she [is] the daughter of my father, but not the daughter of my mother; and she became my wife.Would messiah come through this line if this was a sinful union? How many years from Noah to Abraham were there, and they are still marring close relatives. It was acceptable and not a sin until Moses just my thoughts