Observed and predicted redshift evolution of the offset between SNe from low- and high-mass hosts (log (M/M_⊙) ≶ 10), i.e the “mass step”. Top: black markers show the observed mass step offset per redshift bin (delimited by gray vertical lines). Error bars in redshift represent the dispersion within each redshift bin. The black line is the prediction from Eq. (5), whose amplitude has been set to the SNfactory mass step amplitude at z = 0.05 (filled-cyan triangle). Bottom: distribution of the of SNe Ia from low- (filled-yellow) and high-mass (open-purple) hosts. The left histograms correspond to the closest SNe (z < 0.18) while the right ones are for the highest-z SNe (z > 0.6). The difference within a redshift bin of the mean value for low- and high-mass distributions defines the mass step at this redshift, as plotted in the upper panel.