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We carry out a systematic investigation of the total mass density profile ofmassive (Mstar~3e11 Msun) early-type galaxies and its dependence on redshift,specifically in the range 0<z<1. We start from a large sample of SDSSearly-type galaxies with stellar masses and effective radii measured assumingtwo different profiles, de Vaucouleurs and S\'{e}rsic. We assign dark matterhaloes to galaxies via abundance matching relations with standard LCDM profilesand concentrations. We then compute the total, mass-weighted density slope atthe effective radius gamma', and study its redshift dependence at fixed stellarmass. We find that a necessary condition to induce an increasingly flattergamma' at higher redshifts, as suggested by current strong lensing data, is toallow the intrinsic stellar profile of massive galaxies to be S\'{e}rsic andthe input S\'{e}rsic index n to vary with redshift approximately asn(z)~(1+z)^(-1). This conclusion holds irrespective of the input Mstar-Mhalorelation, the assumed stellar initial mass function, or even the chosen levelof adiabatic contraction in the model. Secondary contributors to the observedredshift evolution of gamma' may come from an increased contribution at higherredshifts of adiabatic contraction and/or bottom-light stellar initial massfunctions. The strong lensing selection effects we have simulated seem not tocontribute to this effect. A steadily increasing S\'{e}rsic index with cosmictime is supported by independent observations, though it is not yet clearwhether cosmological hierarchical models (e.g., mergers) are capable ofreproducing such a fast and sharp evolution.

Revisiting the bulge-halo conspiracy II: Towards explaining its puzzling dependence on redshift