1 When mankind began to multiply on the surface of the entire earth and daughters were born to them, the angels of the Lord — in a certain (year) of this jubilee — saw that they were beautiful to look at. So they married of them whomever they chose. They gave birth to children for them and they were giants. 2 Wickedness increased on the earth. All animate beings corrupted their way — (everyone of them) from people to cattle, animals, birds, and everything that moves about on the ground. All of them corrupted their way and their prescribed course. They began to devour one another, and wickedness increased on the earth. Every thought of all mankind's knowledge was evil like this all the time. 3 The Lord saw that the earth was corrupt, (that) all animate beings had corrupted their prescribed course, and (that) all of them — everyone that was on the earth — had acted wickedly before his eyes.

Similarly, Isaac told Jacob: Arise! Go to Padan-aram, to seek a wife proper for him. He did not wish him to be like the men of the generation of the flood, who wallowed in unchastity and indulged in sexual intercourse with species other than their own. Observe what is written concerning them: The sons of God saw the daughters of men … and took them wives, whomsoever they chose. That was the reason they were obliterated from the earth. The animals, likewise, copulated with species other than their own: the horse with the ass, the ass with the horse, and the serpent with the bird, as it is said: And God saw the earth, and behold, it was corrupt; for all flesh had corrupted their way upon the earth. Notice that Scripture does not say in this verse “all man” but all flesh. Therefore, He blotted out every living substance which was upon the face of the ground, both man and cattle. No being that had copulated with a species other than its own entered the ark, as it is said: From all the pure cattle. Because the ark could harbor only pure beings, they came from among those alone, as it is said: Two and two unto Noah.