Metallicity gradients of the lensed galaxies (red circles) compared to equivalent samples at other redshifts. The x-axis is linear in cosmic time with corresponding redshifts shown on the upper axis. The galaxies shown here are a subset of those in Figure 8 and the symbols are identical. For the MASSIV sample, filled triangles correspond to sources with linear extent >3 × the FWHM of the data while empty triangles have coarser spatial sampling. Comparison samples are selected to occupy the same dark matter halos as the lensed galaxies based on galaxy stellar mass; the corresponding stellar masses at z = 1.2 and z = 0 are noted at the bottom right of each panel. Samples at z = 0 are plotted with slight offsets in redshift for ease of viewing. We also show the time evolution of the Milky Way metallicity gradient measured by Maciel et al. (2003) in the appropriate panel.