We examine the central-galaxy luminosity -- host-halo mass relation for 54 Brightest Group Galaxies (BGGs) and 92 Brightest Cluster Galaxies (BCGs) at z<0.1 and present the first measurement of this relation for a sample of known BCGs at 0.1<z<0.8 (average z~0.3). At z<0.1 we find L_K propto M_{200}^{0.24pm0.08} for the BCGs and the early-type BGGs in groups with extended X-ray emission and L_K propto M_{200}^{0.11pm0.10} for the BCGs alone. At 0.1<z<0.8 we find L_K propto M_{200}^{0.28pm0.11}. We conclude that there is no evidence for evolution in this relationship between z<0.1 and z<0.8: BCG growth appears to still be limited by the timescale for dynamical friction at these earlier times, not proceeding according to the predictions of current semi-analytic models.
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