Abstract

The relevance of the Two-Brains Hypothesis for induction between peripheral Schwann cells and their axon hosts and for intra- and trans-cranial bioengineering at the human-robotics interface is accompanied by particular attention to its significance for a biological wonder: the involvement of geomagnetism in avian directional behavior in migration, homing and navigation. Two sources of magnetism are considered here. The simpler is the polar (compass) direction, long reported as resulting in some birds in a manner unknown from the presence of magnetite (Fe3O4) in the avian ethmoid region. The second is certain chemical reactions that respond to applied magnetic fields. These usually involve radicals, molecules with unpaired electrons that spin in one of two possible states. A radical-pair mechanism, a light-dependent, chemical initiation of magnetic orientation, has been considered responsive to the axial inclination of the field in relation to Earth's field, but not to its polarity. The initiation is by optic but non-visually responsive cellular absorption of a photon of a specific wavelength. Radical pairs are short-lived and must be correctly aligned in the host receptors for directional sensitivity. The firmest evidence for the radical-pair theory of magneto-reception in birds remains the cryptochromes, the blue-light absorbing flavoproteins, but the receptor molecule has not been identified yet. Subjective thought and consciousness are also unexplained in birds, as in humans and animals. However, the novel, structured dichotomy of the Two-Brains Hypothesis may provide a fresh, biophysical approach to the connection between geomagnetism, life and the evolution of vertebrate translocation without recourse to philosophy or a universe expanding beyond imagination.