The term sons of God and daughters of men who bore Nephilim which is often translated as giants had fascinated people for thousands of years. The topic was also discussed on another post, Who are the sons of God? Even during the time of Jesus, many often understood this to be a union between angels and humans as we read in the book of Jude.

Does the book of Genesis gives us some clues to identify them?

Text itself says as men

Gen 6:1-6 Now it came to pass, when men began to multiply on the face of the earth, and daughters were born to them, that the sons of God saw the daughters of men, that they were beautiful; and they took wives for themselves of all whom they chose. And the LORD said, “My Spirit shall not strive with man forever, for he is indeed flesh; yet his days shall be one hundred and twenty years.” There were giants on the earth in those days, and also afterward, when the sons of God came in to the daughters of men and they bore [children] to them. Those were the mighty men who were of old, men of renown. Then the LORD saw that the wickedness of man was great in the earth, and that every intent of the thoughts of his heart was only evil continually. And the LORD was sorry that He had made man on the earth, and He was grieved in His heart.

When God said that His Spirit will not strive with man forever, none of the prior wrongdoings mentioned were men’s fault except if sons of God refers to men. Also, the offspring of the strange union were also mentioned as men. If sons of God were just men, why were they not referred as men?

Sons and daughters

Gen 2:23 And Adam said: “This is now bone of my bones And flesh of my flesh; She shall be called Woman, Because she was taken out of Man.

Adam referred initially to Eve as woman because she was from man.

Gen 4:1 Now Adam knew Eve his wife, and she conceived and bore Cain, and said, “I have acquired a man from the LORD.”

When Eve bore Cain, she said that she received him from the LORD. You can clearly see how the mindset of thinking that males were created by God and females were taken from men. 

Gen 3:16 To the woman He said: “I will greatly multiply your sorrow and your conception; In pain you shall bring forth children sons (H1121); Your desire shall be for your husband, And he shall rule over you.”

Gen 3:17-19 Then to Adam He said, “Because you have heeded the voice of your wife, and have eaten from the tree of which I commanded you, saying, ‘You shall not eat of it’: “Cursed is the ground for your sake; In toil you shall eat of it All the days of your life. Both thorns and thistles it shall bring forth for you, And you shall eat the herb of the field. In the sweat of your face you shall eat bread Till you return to the ground, For out of it you were taken; For dust you are, And to dust you shall return.”

If you see the above verses, will women have pain only for delivering sons and not for daughters? No. Also, if women work on the field, does that mean it will not bring them thorns and thistles? Or, will she not turn to dust since it was only a curse for Adam? This is not just in Genesis, but flows throughout he Bible if you remove the gender neutral language used in the Bible .e.g. children for sons.

Isa 3:12 As for My people, children are their oppressors, And women rule over them. O My people! Those who lead you cause you to err, And destroy the way of your paths.”

The mindset of the ancient Israelites based on the Bible is that, God rules over all men as we see in the law, and men rule over women as per the curse of God in Eden. Women who are under men inherits all the curses of men but men do not inherit any curse of women.

Ps 82:6 I said, “You are gods, And all of you are children sons (H1121) of the Most High.

This is the basis for the term that sons of God refers to men who are from God and daughters of men refers to women who were taken out of men.

What about Nephilim?

Gen 6:4 There were giants Nephilim on the earth in those days, and also afterward, when the sons of God came in to the daughters of men and they bore [children] to them. Those were the mighty men who were of old, men of renown.

No one knows what Nephilim actually mean. It is translated as giants. In the above verse, children was a translator added term. 

Num 13:33 “There we saw the giants Nephilim (the descendants of Anak came from the giants); and we were like grasshoppers in our own sight, and so we were in their sight.”

Deut 2:10-11 (The Emim had dwelt there in times past, a people as great and numerous and tall as the Anakim. They were also regarded as giants Raphah,  like the Anakim, but the Moabites call them Emim.

Deut 2:20-21 (That was also regarded as a land of
giants Raphah; giants Raphah formerly dwelt there. But the Ammonites call them Zamzummim, a people as great and numerous and tall as the Anakim. But the LORD destroyed them before them, and they dispossessed them and dwelt in their place,

As you can clearly see, the authors/scribes (or Moses) who wrote Numbers and Deuteronomy held the view that Nephilim survived the flood and able or have Anak as descendants. The other only possible view is that, Nephilim simply means people of tall stature who frighten other people, but not necessarily giants.

Conclusion

In ancient Israel, sons of God refers to men who are from God and daughters of men refers to women who were taken out of men. Hence, there were neither strange unions between angels and women nor their offspring were strange giant hybrids during the antediluvian era.