Chazemataz:
Okay, I’ve cornored them and now the only argument they have left is a good one: Incest can cause humans to become deformed. How come we aren’t all deformed if Adam and Eve’s kids had sex with each other? Aren’t they related?
**First of all, the Bible does not say that Adam and Eve’s children all had sex with each other. There were other human beings around them as well, but the fact is they were the first made and chosen by God. This is the reason why the Catholic Church allows us to take the story of creation in Genesis as symbolic. **
1The man had relations with his wife Eve, and she conceived and bore Cain, saying, “I have produced a man with the help of the LORD.”
2 Next she bore his brother Abel. Abel became a keeper of flocks, and Cain a tiller of the soil. - Gen 4:1-2
Clearly here the Man is Adam who had sex with Eve to give birth to Abel and Cain. Later on…
17Cain had relations with his wife, and she conceived and bore Enoch. Cain also became the founder of a city, which he named after his son Enoch.
18 To Enoch was born Irad, and Irad became the father of Mehujael; Mehujael became the father of Methusael, and Methusael became the father of Lamech. 19 Lamech took two wives; the name of the first was Adah, and the name of the second Zillah. 20 Adah gave birth to Jabal, the ancestor of all who dwell in tents and keep cattle. 21 His brother’s name was Jubal; he was the ancestor of all who play the lyre and the pipe. 22 Zillah, on her part, gave birth to Tubalcain, the ancestor of all who forge instruments of bronze and iron. The sister of Tubalcain was Naamah. 23 Lamech said to his wives: “Adah and Zillah, hear my voice; wives of Lamech, listen to my utterance: I have killed a man for wounding me, a boy for bruising me. 24 If Cain is avenged sevenfold, then Lamech seventy-sevenfold.” 25
6 Adam again had relations with his wife, and she gave birth to a son whom she called Seth. “God has granted me more offspring in place of Abel,” she said, “because Cain slew him.” 26 To Seth, in turn, a son was born, and he named him Enosh. At that time men began to invoke the LORD by name. - Gen. 4:17-26
Clearly here, where did that other woman come from in which Cain had sex with? It isn’t recorded where she came from and obviously the only children Adam and Eve had at this point were Cain, Abel (who Cain killed), and Seth, all male. This proves that God made other people as well after the departure from the Garden of Eden. However, that fact isn’t recorded. There are questions that are unanswered, we call them "mysteries."
1
1 When men began to multiply on earth and daughters were born to them, 2
2 the sons of heaven saw how beautiful the daughters of man were, and so they took for their wives as many of them as they chose.- Gen 6:1-2
Notice here, “the daughters of man” and “the sons of heaven.” Clearly, this is telling us that there were men that were from heaven (in other words made by God) and women that were the offspring of men already made. The men from heaven married the daughters of men.