  The dust content of normal galaxies and the dust mass density (DMD) at high-z
(z>4) are unconstrained given the source confusion and the sensitivity
limitations of previous observations. The ALMA Large Program to INvestigate
[CII] at Early Times (ALPINE), which targeted 118 UV-selected star-forming
galaxies at 4.4<z<5.9, provides a new opportunity to tackle this issue for the
first time with a statistically robust dataset. We have exploited the
rest-frame far-infrared (FIR) fluxes of the 23 continuum individually detected
galaxies and stacks of continuum images to measure the dust content of the 118
UV-selected ALPINE galaxies. We have focused on the dust scaling relations and,
by comparing them with predictions from chemical evolution models, we have
probed the evolutionary stage of UV-selected galaxies at high-z. By using the
observed correlation between the UV-luminosity and the dust mass, we have
estimated the DMD of UV-selected galaxies at z~5, weighting the galaxies by
means of the UV-luminosity function (UVLF). The derived DMD has been compared
with the value we have estimated from the 10 ALPINE far-IR continuum blindly
detected galaxies at the redshift of the ALPINE targets. The comparison of the
observed dust scaling relations with chemical evolution models suggests that
ALPINE galaxies are not likely progenitors of disc galaxies, but of
intermediate and low mass proto-spheroids, resulting in present-day bulges of
spiral or elliptical galaxies. Interestingly, this conclusion is in line with
the independent morphological analysis, that shows that the majority (~70\%) of
the dust-continuum detected galaxies have a disturbed morphology. The DMD
obtained at z~5 from UV-selected sources is ~30% of the value obtained from
blind far-IR selected sources, showing that the UV-selection misses the most
dust-rich, UV-obscured galaxies.
