There is a lot of sex in the Bible including incest. See a few of the incestuous narrations:
“And Cain went out from the face of the Lord, and dwelt as a fugitive on the earth, at the east side of Eden. And Cain knew his wife, and she conceived, and brought forth Henoch: and he built a city, and called the name thereof by the name of his son Henoch.” (Genesis 4:16-17
Cain was the first born son of Adam and Eve, and Abel was the second. In the fourth chapter of Genesis we read how Cain kills his brother and is sent east of Eden where he “lays” with a woman. Because Adam and Eve were the first humans – from whom all people come – Cain’s woman was either his sister which cannot be as there is no mention of a sister to Cain until this incident. So the woman had to be Eve herself–his own mother. All the early Biblical relationships were incestuous –either between son and mother or between brother and sister (with the exception of Adam and Eve). God wanted incest to happen (he could have created a number of women and men so that incest never happened).
Abraham marries his half-sister
Howbeit, the daughter of my father, and not the daughter of my mother, and I took her to wife. And after God brought me out of my father’s house, I said to her: Thou shalt do me this kindness: In every place, to which we shall come, thou shalt say that I am thy brother. (Genesis 20:12-13
Abraham married his half-sister Sara in Ur. The King of Gerara took her from Abraham, Annoyed, God sent the King a dream to tell him that he would be destroyed for taking a woman who already had a husband. This shows that God approved of the marriage between the brother and sister. The King returned Sara to Abraham and they remained together as a couple until she died at the age of 127 and Abraham died 38 years later at 175.
Lot has sex with and his daughters
“And the elder daughter said to the younger one: ‘Our father is old, and there is no man left on the earth, to come in unto us after the manner of the whole earth. Come, let us make him drunk with wine, and let us lie with him, that we may preserve seed of our father.’ And they made their father drink wine that night: and the elder went in and lay with her father: but he perceived not neither when his daughter lay down, nor when she rose up. And the next day the elder said to the younger: Behold I lay last night with my father, let us make him drink wine also to night, and thou shalt lie with him, that we may save seed of our father. They made their father drink wine that night also, and the younger daughter went in, and lay with him: and neither then did he perceive when she lay down, nor when she rose up. So the two daughters of Lot were with child by their father. (Genesis 19:31-36
The two daughters had sex with their father and Lot could thus preserve his family line. Incidentally, this all happened shortly after they had fled from Soddom and Gomorrah which was destroyed by God for its immorality. Nine months later, the daughters gave birth to two sons, Moab (father of the Moabites), and Ammon (father of the Ammonites).
Nachor marries his niece
And Thare lived seventy years, and begot Abram, and Nachor, and Aran. And these are the generations of Thare: Thare begot Abram, Nachor, and Aran. And Aran begot Lot. And Aran died before Thare his father, in the land of his nativity in Ur of the Chaldees. And Abram and Nachor married wives: the name of Abram’s wife was Sarai: and the name of Nachor’s wife, Melcha, the daughter of Aran, father of Melcha, and father of Jescha. (Genesis 11:26-29
This is one of those complex ‘generations’ quotes that are found throughout the early stages of the Bible, but if you pay close attention you can see that Nachor (Abraham’s brother) married Melcha (his niece). Phrases like these cover up incest in a number of places.
"And Er, Judah's firstborn, was wicked in the sight of the LORD; and the LORD slew him. And Judah said unto Onan, Go in unto thy brother's wife, and marry her, and raise up seed to thy brother. And Onan knew that the seed should not be his; and it came to pass, when he went in unto his brother's wife, that he spilled it on the ground, lest that he should give seed to his brother. And the thing which he did displeased the LORD: wherefore he slew him also." (Genesis 38:7-10)
According to interpretations of the Bible, Onan removed his penis from his partner's vagina before he ejaculated so that his seed fell onto the ground and for this God slew him. If someone refuses to commit incest, God kills him!