Genesis 6:1 And it happened, when people began to multiply on the face of the earth, and they had daughters, 2the angels noticed how beautiful the women were, and snatched wives for themselves of all whom they fancied. 3And the Lord said, “My spirit will not always put up with people, because they are corrupt and so I’ll allow them another 120 years.” 4There were giants in the earth back then and also later. When the angels slept with women and they gave birth to their children, they became the famous heroes of ancient legends. 5And God saw that people’s wickedness overwhelmed the earth, and that everything they thought, and their deepest imaginations were entirely and continuously evil. 6The Lord regretted that he had made people on the earth, and he was heartbroken. 7The Lord said, “I will destroy the people I’ve created from the face of the earth; people, animals, bugs and the birds of the air; since I regret that I have made them.” 8But the Lord was delighted with Noah. 9This is the story of Noah. Noah was a godly man and perfect in his time, and Noah walked with God. 10And Noah had three sons, Shem, Ham, and Japheth. 11The earth was corrupt in God’s eyes, and the earth was filled with violence. 12God looked at the earth and saw that it was corrupt; for all life on the earth had become corrupt. 13God said to Noah, “I’m going to destroy all life on the earth because it is filled with their violence. Look! I’ll wipe them out with the earth.”
When it’s translated like that, it seems really weird, but so is the virgin birth and people rising from the dead. We serve a supernatural God. Those who reject the historicity of the Bible have particular problems with this narrative and twist it in all kinds of ways to avoid the obvious interpretation. But the evidence abounds of creatures great and small preserved by the catastrophic flood that killed them all around the world.
The biblical narrative is supported by other ancient writings. In particular, the book of Enoch, which is quoted by Jude and referenced by Peter, was considered for inclusion in the Bible. It was preserved in the apocrypha of the Ethiopian bible and in the dead sea scrolls. The book of Enoch describes how 200 angels were appointed to nurture mankind. However, they made a pact to indulge themselves with humans. As punishment, they were to witness their offspring destroy each other in a civil war before they would be bound up until their eternal punishment. They were called Nephilim in Hebrew, which means fallen ones. Most bibles translate this word as giants. The offspring of Nephilim are called Rephaim.
After the flood, we see there were giants again.
Numbers 13:33 And there we saw the giants, the sons of Anak, which come from the giants. And we felt like grasshoppers in our own sight, and in their sight also.
According to https://answersingenesis.org/bible-characters/giants-in-the-old-testament/ there were many other giants recorded in extra-biblical writings – up to 9 meters tall. Commentators suggest that the giants got shorter as their genes were diluted – Goliath was two thirds of King Og’s height some generations later.
Many other historic sources and legends from around the world remember giants. Somehow, they’re always the bad guys, of vicious character. I’ve heard that the native American greeting showing the hand was proof that they didn’t have six fingers like Goliath’s brother
2 Samuel 21:20 And there was another battle in Gath, where there was a man of great stature, that had on every hand six fingers, and on every foot six toes, four and twenty in number; and he also was born to the giant.
Jude and Peter refer to these angels who corrupted the people leading to Noah’s flood.
Jude 1:6 And the angels which abandoned their assigned post, and left their own quarters, he’s kept in everlasting chains under darkness until the judgment of the great day.
2 Peter 2:4 If God didn’t spare the angels that sinned, but cast them down to hell, and bound them in chains of darkness, to be reserved for judgment…
The book of Jasher is another respected extra-biblical text which has been preserved with the dead sea scrolls. Joshua 10:13 and 2 Samuel 1:18 both refer to this book as authoritative for collaborating biblical events.
I conclude from reading these sources, that so much genetic experimentation had happened that all life was genetically corrupt. God had to step in before there was no hope for life on Earth. We see this reflected in
Leviticus 19:19 Obey my laws. Don’t crossbreed different kinds of animals. Don’t sow your field with different kinds of seeds.
This should serve as a warning to our foray into genetic engineering – that there are limits that must not be crossed. While such technology within appropriate bounds is hugely beneficial, mixing DNA from one kind of animal into another has dangerous unforeseeable consequences.
Contrary to this warning, we are embracing such things. There is great profit to make from such technologies, which various companies are scrambling to monopolize before their competitors. Spider DNA is inserted into goats to produce an animal which excretes super-strong thread. Of course, military application in breeding super-soldiers is very alluring, particularly to nations with less godly moral constraints. What if we could breed 10-meter giants to fight our battles?
I foresee that as the bad gets badder, unholy genetic manipulation will corrupt all life over the next few generations. This will contribute to increasing violence throughout the world. This could be a factor in the mark of the beast, rendering those taking the mark incapable of turning back to God. By the end of the tribulation God will have to destroy all genetically corrupt life. But Jesus will restore those who kept themselves pure, to live with him through his millennial reign over a restored creation.