Do not "aliens" mate with women, produce mixed children..?
It's recognized as a repeatedly demonstrated, proven scientific fact that greater oxygen and higher air pressure promote exorbitantly greater growth in organisms.
Scientists attribute the great size of the dinosaurs to the theory that "millions of years ago" the earth's atmosphere contained 33% higher oxygen saturation and much greater atmospheric pressure than it does today.
Not to mention the many fossilized animals found that are exact duplicates of modern day species, yet anywhere from 2 to 10 times larger!
There are good reasons to believe that giants lived in the land, and that they were regular human beings. For one, the oxygen content and air pressure were much greater in the past. Secular scientists agree to as much, and Biblical Creationists concur, and point to the "fountains of the great deep" and the "floodgates of heaven" from Genesis 7:11 to show that their idea is very tenable Biblically.
Naturally, human beings and other animals would no longer be able to grow to the sizes that were possible in the pre-flood world, or at least not with the same frequency, since the the floodgates of heaven (believed by Biblical Creationists to have been a canopy of water around the earth in the upper atmosphere) are no longer present to cause the favourable greenhouse conditions necessary for such growth.
Finally, if none of the has given you pause, then I ask you in all seriousness:
How does a spiritual being (having no physical form) share its 'DNA' with a corporal being?
Does it 'create' for itself a body and DNA, as though God were not the only being capable of creating?
Which of the following men have 'demon blood'
in their veins?
How could the 'demon blood' have survived the flood?