The hybrids were a humanoid species directly descended from those Isu who chose to interbreed with their human workforce. As a result of this interbreeding, hybrids were born without the artifical neurotransmitters that forced humanity's subservience to their Piece of Eden-wielding Isu overlords.
Over the subsequent generations, the hybrids and their offsprings were assimilated into the general human population. Resultantly, the concentration of Isu DNA in their own genome became diluted with each generation. Certain bloodlines directly descended from the hybrids, however, possessed fractionally higher levels of Isu DNA in their genome–resting somewhere between the 0.0002% of normal humans, to the 5 or 6% of Sages–which allowed their scions to naturally access Eagle Vision or to more fully interact with Pieces of Eden, much like their ancestors had.