  The observed fraction of pulsars with interpulses, their period distribution
and the observed pulse width versus pulse period correlation is shown to be
inconsistent with a model in which the angle alpha between the magnetic axis
and the rotation axis is random. This conclusion appears to be unavoidable,
even when non-circular beams are considered. Allowing the magnetic axis to
align from a random distribution at birth with a timescale of 70 Myrs years
can, however, explain those observations well. The timescale derived is
consistent with that obtained via independent methods. The probability that a
pulsar beam intersects the line of sight is a function of the angle alpha and
therefore beam evolution has important consequences for evolutionary models and
for estimations of the total number of neutron stars. The validity of the
standard formula for the spin-down rate, which is independent of alpha appears
to be questionable.
