The origin of recently discovered reverse (opposite-sign) dark resonances h
as been explained theoretically and verified experimentally. It is shown th
at the reason for these resonances is a specific optical pumping of the gro
und state magnetic sublevel in a transition when the ground state angular m
omentum is smaller than the excited state momentum. An experiment was condu
cted on Rb-85 atoms in a cell, when a diode laser using the ground state hy
perfine level F-g = 3 simultaneously excites spectrally unresolved hyperfin
e levels with total angular momentum quantum numbers F-e = 2, 3 and 4. It i
s shown that due to differences in the transition probabilities the dominan
t role in total absorption and fluorescence signals is played by absorption
on a transition F-g = 3 --> F-e = 4.