English: For many angels of God now consorted with women and begat sons who were overbearing and disdainful of every virtue, such confidence had they in their strength; in fact the deeds that tradition ascribes to them resemble the audacious exploits told by the Greeks of the giants. (Jewish Antiquities, I, 73)
Greek: πολλοὶγὰρ ἄγγελοι θεοῦ γυναιξὶ συνιόντες τὸνβίον συνεδρίου παῖδας καὶπαντὸς ὑπερόπτας καλοῦ διὰ τὴν ἐπὶ τῇ δυνάμει πεποίθησιν· ὅμοιατοῖς ὑπὸ γιγάντων τετολμῆσθαι λεγομένοις ὑφ᾿ Ἑλλήνων καὶ οὗτοιδράσαι παραδίδονται. (Loeb #242, p. 35)
Examples: Centaur, Minotaur, etc. Whatever happened, this appears to have happened before the flood of Noah (with some additional references after the flood).
Until the 4th century A.D.: Angels had relations with humans to create hybrids. (Josephus)
Introduced in the 4th century A.D.: Sons of Seth married the daughters of Cain. (Augustine)
Genetic engineering before the flood: In Genesis 5 and as recorded by Josephus in the first century, these fallen angels appear to have consorted (had relations) with women. This "
genetic" engineering created hybrids and was, in part, the reason for the flood of Noah. Noah was not "
perfect" but his genes were not corrupted.