Upper panel: Redshift evolution of the fraction of MBHs in a given stellar mass bin that underwent a growth episode via minor merger (f_min merg). Middle panel: Redshift evolution of the fraction of MBHs in a given stellar mass bin that experienced a growth phase after a major merger (f_{maj,  merg}). Lower panel: Redshift evolution of the fraction of MBHs in a given stellar mass bin that had a growth phase after a disc instability (f_DI). The colour coding and mass dependence are the same as in Fig. 4. A major merger is defined as a galaxy interaction whose baryonic (gas+stars) mass ratio is larger than 0.2. Otherwise, the interaction is tagged as a minor merger.