  We evaluate with numerical simulations the hypothesis that BL Lacertae
objects are the remnants of Quasi Stellar Objects. This hypothesis is based on
their highly peculiar redshift evolution. They have a comoving space density
that increases with decreasing redshift, contrary to all other active galactic
nuclei. We assume that relativistic jets are below detection in young
radio-quiet quasars and increase in strength with cosmic time so that they
eventually are detected as BL Lacertae objects. Our numerical simulations fit
very well the observed redshift distributions of BL Lacertae objects. There are
strong indications that only the high-synchrotron-peaked BL Lacertae objects
could be QSO remnants.
