hmm. I was always pretty partial to the theory that the Zeal family are the descendants of the Iubarians.
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Someone mentioned that the Ioka would have eventually come in contact with the Frozen Flame for the Earthbounds in 12,000 BC to "not talk like Ayla." I wouldn't necessarily agree with that since the Reptites evolved on their own just fine, and the Ioka DID have several million years to evolve into the Earthbound tribe...
However it could be possible that the Ioka turned to Zeal and the Iuba turned to Earthbound; I suppose that could have happened just as easily.
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But yes...the bloodline. I believe that whomever was the Ayla/Kino descendant in 12000 may have found the pendant from the ruins of the Oceanpalace... That pendant was made from the red rock, the dream stone, the same material as the frozen flame, perhaps? In CT they mention that the red rock has the power to transform a human when in contact with that human.
Say the pendant has but a small amount of power left within it. Whomever picked that pendant up may have been transformed, and perhaps into a charismatic leader, hence the start of the Guardia line....? Seeing that the pendant played such a part in the leader's life, it may have become an important heirloom. It was very important to Marle, afterall.