  Motivated by recent results on the location of the radio emission in pulsar
magnetospheres, we have developed a model which can account for the large
diversity found in the average profile shapes of pulsars. At the centre of our
model lies the idea that radio emission at a particular frequency arises from a
wide range of altitudes above the surface of the star and that it is confined
to a region close to the last open field lines. We assert that the radial
height range over which emission occurs is responsible for the complex average
pulse shapes rather than the transverse (longitudinal) range proposed in most
current models. By implementing an abrupt change in the height range to
discriminate between young, short-period, highly-energetic pulsars and their
older counterparts, we obtain the observed transition between the simple and
complex average pulse profiles observed in each group respectively. Monte Carlo
simulations are used to demonstrate the match of our model to real
observations.
