Observations suggest that high-redshift galaxies are either very dusty or essentially dust free .
The evolution from one regime to the other must also be very fast , since evolved and dusty galaxies show up at redshifts corresponding to a Universe which is only about 500 Myr old .
In the present paper models which predicts the existence of an apparent dichotomy between dusty and dust-free galaxies at high redshift are considered .
Galaxies become dusty as soon as they reach an evolved state and the transition is very rapid .
A special case suggests that while stellar dust production is overall relatively insignificant – contrary to what has been argued recently – it can at the same time be consistent with efficient dust production in supernovae in the local Universe .
Special attention will be given to the recent discovery of a dusty normal galaxy ( A1689-zD1 ) at a very high redshift z = 7.5 \pm 0.2 .