From Daniel 2:43 (New King James)
43 As you saw iron mixed with ceramic clay, they will mingle with the seed of men; but they will not adhere to one another, just as iron does not mix with clay.
The word translated "mingle" means "mix". The clay (= the seed of men) mixes with iron (="they"). Many of the Google search results for this verse claim that the contrast between "they" and "seed of men" indicates that the "they" cannot be human. Thus the "mingling" is the sexual relationship between demons and humans, as in Gen 6:1-4. I do not believe this conclusion is warranted. The word translated "mingling" does not mean sexual contact, but simply a mixing, as the mixing of iron with clay. Rather, as the gold, silver, and bronze all represent humans, so do the iron and clay.
John Gill offers the following explanation:
Whether or not one agrees with the details of Gill's applications of this prophecy to specific nations and intermarriages, his basic interpretation remains solid. In my opinion, anyway.
Some of those who believe that the book of Revelation is future yet to be fulfilled link the "seeds of men" with and Satan and the angels who are cast to earth on the basis of Revelation 12:7-12
This is believed to be of a future fall.
This view is also supported by Revelation 16
So from a futurist literal point of view there will be definitely other beings on earth during this time.....which then concurs with Daniel.
Last but not least pseudepigraphal books such as Enoch mention other entities on the scene during end times:
And 2 Baruch 27:1-14 appears to describe these entities as well:
As such, these "seeds of men" appear to be some type of creature strange creature mentioned in the several writings which discuss the end times.
Man was created from the Earth, therefore Man is Dust/Clay. I have always pondered the question of 'They', and posited that the 'They' may very well be the seed of Satan, that has survived and mingled with Men. we are told that we struggle not with 'Flesh and Blood' but rather with Powers, Principalities and Thrones. When flesh/clay (the daughters of men) was mingled with iron (the Fallen Ones ?), the product of that union was the giants, a race of supermen that dominated mankind (flesh/clay).
Of that entire generation we find that Moses was the only 'uncorrupted' remaining on the earth, yet after the deluge we again find Israel encountering the children of anak, the amorites in the land. In the book of Amos, when the Lord testifies against the ungratefulness of Israel, we get a glimpse of the dimension of the Iron men " Yet destroyed I the Amorite before them, whose height was like the height of the cedars, and he was strong as the oaks; yet I destroyed his fruit from above, and his roots from beneath."
Could it be that the seed of Satan existed among the Romans and successive powers to this day ?