Are BL Lacertae Objects Beamed QSO Remnants?
  This paper considers the hypothesis that BL Lacertae objects (BLLs) are the beamed remnants of Quasi Stellar Objects. The hypothesis explains why BLLs do not undergo the strong evolution seen in other active galactic nuclei since it naturally predicts that the space density of BLLs should increase with cosmic time, as shown by recent observations. Numerical models reproduce, with reasonable parameters, the known redshift and magnitude counts of BL Lac objects. It is assumed that radio-quiet as well as radio-loud quasars are capable of generating jets but that jets are snuffed in young radio-quiet objects and only emerge in aged ones. I argue that the observations allow this assumption. 
E.F. Borra