Mass ratio evolution with redshift: joy plot (a) and tomography (b). Both panels report the median distribution only: an animated version of this plot including the 68% credible regions is available online along with plots showing individual slices. This distribution, set aside an excess at low redshifts (z ≲ 0.2), is consistent throughout the whole redshift spectrum in having support at around 0.7, with negligible support for q = 1.