Evolution of the black mass density. Shown are samples of the Type 1 AGN mass density predicted by the model, same as in Figure 13c (grey), as well as the estimated total black hole mass density calculated by integrating the model QLF over cosmic time (pink). Shown on the left are the observational estimates for the Type 1 AGN mass density (grey, Mullaney et al. 2012) and total black hole mass density (pink, Shankar et al. 2009) at z = 0.