2. Brain-type series. The one physical uniformity of mortals is the brain and nervous system; nevertheless, there are three basic organizations of the brain mechanism: the one-, the two-, and the three-brained types. Urantians are of the two-brained type, somewhat more imaginative, adventurous, and philosophical than the one-brained mortals but somewhat less spiritual, ethical, and worshipful than the three-brained orders. These brain differences characterize even the prehuman animal existences.
From the two-hemisphere type of the Urantian cerebral cortex you can, by analogy, grasp something of the one-brained type. The third brain of the three-brained orders is best conceived as an evolvement of your lower or rudimentary form of brain, which is developed to the point where it functions chiefly in control of physical activities, leaving the two superior brains free for higher engagements: one for intellectual functions and the other for the spiritual-counterparting activities of the Thought Adjuster.
While the terrestrial attainments of the one-brained races are slightly limited in comparison with the two-brained orders, the older planets of the three-brained group exhibit civilizations that would astound Urantians, and which would somewhat shame yours by comparison. In mechanical development and material civilization, even in intellectual progress, the two-brained mortal worlds are able to equal the three-brained spheres. But in the higher control of mind and development of intellectual and spiritual reciprocation, you are somewhat inferior.
All such comparative estimates concerning the intellectual progress or the spiritual attainments of any world or group of worlds should in fairness recognize planetary age; much, very much, depends on age, the help of the biologic uplifters, and the subsequent missions of the various orders of the divine Sons.
While the three-brained peoples are capable of a slightly higher planetary evolution than either the one- or two-brained orders, all have the same type of life plasm and carry on planetary activities in very similar ways, much as do human beings on Urantia. These three types of mortals are distributed throughout the worlds of the local systems. In the majority of cases planetary conditions had very little to do with the decisions of the Life Carriers to project these varied orders of mortals on the different worlds; it is a prerogative of the Life Carriers thus to plan and execute.
These three orders stand on an equal footing in the ascension career. Each must traverse the same intellectual scale of development, and each must master the same spiritual tests of progression. The system administration and the constellation overcontrol of these different worlds are uniformly free from discrimination; even the regimes of the Planetary Princes are identical.
3. Spirit-reception series. There are three groups of mind design as related to contact with spirit affairs. This classification does not refer to the one-, two-, and three-brained orders of mortals; it refers primarily to gland chemistry, more particularly to the organization of certain glands comparable to the pituitary bodies. The races on some worlds have one gland, on others two, as do Urantians, while on still other spheres the races have three of these unique bodies. The inherent imagination and spiritual receptivity is definitely influenced by this differential chemical endowment.
Of the spirit-reception types, sixty-five per cent are of the second group, like the Urantia races. Twelve per cent are of the first type, naturally less receptive,
