Dr. Hugh Ross of Reasons to Believe has a good answer. He says, “Given that we are all descended from Adam and Eve, either Cain or one of his brothers must have married a sister. This would seem to violate the commands recorded in the book of Leviticus forbidding marriage between brothers and sisters. The Levitical laws, however, must be considered in their proper historical context. Though the book of Genesis condemns sexual relations between children and their parents, it nowhere prohibits a man from marrying his sister or niece. Abraham, for example, married his half-sister without compunction. Not until the time of Moses were laws established forbidding a man from marrying a sister or niece. The timing of this command makes perfect sense biologically, for genetic defects as a result of intra-family marriage would not begin to crop up until after the first few dozen generations.”
In a nutshell, though sex between parents and their children has always been out of the question, marriage between other close relatives was permitted until the time of Moses. Practically, this makes sense because as Adam and Eve’s offspring married each other the human population possibly grew to almost 5 billion within a generation (see article mentioned above)! Scientifically, this make sense in terms of the genetic defects that would have begun to arise on a grand scale if new restrictions had not been put in place. This is a good example of one of God’s moral laws (and its timing) making very good scientific sense.
SCRAMBLED AGE 
What ridiculous poppy cock!!! There is no proof that people could ever live to be 900 yrs. old, other than in that ridiculous story book called the bible. The fact is that the so-called god may or may not have created the most disgusting species on earth and made the unbelievable mistake of not thinking through that 2 people and thousands of eggs call for immense incest.
What else was there to do in that paradise than procreate with whatever moved? It is beyond me that anyone in his right mind can believe this utter nonsense!
All of you religious believers had made sure that the world is one intolerant, violent and horrible place. And if there actually would be some allmighty Being who had created this unbelievable mess of horrors, couldn’t he have done more than the tricks performed in that bible book, such as transforming people into salt pillars or saving pairs of certain species in a home-built boat?
Come on, a couple of tricks and for the rest he was probably enjoying the spectacle of all the misery and murder that have been happening ever since.
I would like to believe there would be a god, a good god, but if there is one, it is one evil monster who came up with one stupid creation plan. Give me a Dog any time and may all of you who actually believe this insanity get your brains working one of these days soon. And stop fighting each other over all the different and ridiculous religions you believe in without having any compassion or tolerance for each other. Bah, if it all did start with two stupid beings committing incest, the world’s population has deteriorated a million fold. All of what we suffer through nowadays began with one stupid apple?????/
Insanity thy name is man……. and god, since we’re all made in the name of the latter.
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