It seems half of all humans are not spiritually developed...

[Ankh]

Do you think that Ra was speaking of native third density entities making the choice of their own life plans for incarnations, or making that choice of polarity?

In those particular quotes Don and Ra speak of these things:

During the first portion of third-density cycles, incarnations are automatic and occur rapidly upon the cessation of energy complex of the physical vehicle. There is small need to review or to heal the experiences of the incarnation. As, what you would call, the energy centers begin to be activated to a higher extent, more of the content of experience during incarnation deals with the lessons of love.

Thus the time, as you may understand it, between incarnations is lengthened to give appropriate attention to the review and the healing of experiences of the previous incarnation. At some point in third density, the green-ray energy center becomes activated and at that point incarnation ceases to be automatic.

21.10 Questioner: When incarnation ceases to become automatic I am assuming that the entity can decide when he needs to reincarnate for his— the benefit of his own learning. Does he also select his parents?

Ra: I am Ra. This is correct.