Number density evolution of massive (M_⋆ ≥ 10^11.25  M_⊙) ETGs (E/S0) as a function of redshift from Buitrago et al. (2013, pentagons) and Pozzetti et al. (2010, squares). The dashed line is the expected number density evolution due to gas-rich (wet) major mergers from our model. The solid line is the expected number density evolution due to wet major and dry mergers (both major and minor) from our model. Mergers are common enough to drive the number density evolution of massive ETGs since z ~ 1.3. (A colour version of this plot is available at the electronic edition.)