Genesis 6:3

And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them,

That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.

There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.

And GOD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually.