The Book of Genesis also alludes to all this prior to the Flood. It speaks of "men of renown" and "heroes of old" who were the result of offspring between the "gods" (fallen angels, probably calling themselves Zeus and so on) and human women. There are also archaeological indications in various ancient world civilisations of human/animal hybrids (ancient Egypt, for example), which would explain things like minotaurs. Again, the Book of Enoch hints at fallen angels breeding animals and humans too, or at genetic engineering. Fascinating stuff.