The Schuster-Blackett (S-B) conjecture, which supposes the relationshipM/J=βG 1/2 /2c between the magnetic dipole moments (M) of celestial objects and their angular momenta (J), where G is the Newtonian constant of gravitation, c the speed of light, and β a dimensionless constant of order unity, is examined in the context of the evolution of pulsar gyromagnetic ratios. It is demonstrated that the evolution of pulsar gyromagnetic ratios is not consistent with the strong form of the S-B conjecture where β is (...) taken to be a constant. The pulsar evidence, which shows evolution withM/J constant for individual short-period pulsars, however, does admit the validity of a weaker form of the S-B conjecture, where β is allowed to take on a range of values. It is also shown that the only conventional explanation of the origin of pulsar magnetic fields that produces evolution where the gyromagnetic ratio remains constant for individual pulsars which generates magnetic fields of sufficient strength, the thermally driven Hall-field-limited battery effect, may not convincingly account for the observed behavior of pulsars. A few of the implications of the S-B conjecture and the pulsar evidence are explored. (shrink)