Sexual selection is a competition between conspecific individuals to acquir
e mates and maximize their reproductive success. This can lead to the devel
opment of conspicuous secondary sexual traits under several possible mechan
isms. Since these sexual characters can be used as potential discriminant f
eatures in species recognition, it seems legitimate to think of a potential
role of sexual selection in population divergence. Here I review several e
mpirical studies and models that try to show how important sexual selection
can be in speciation processes. The emergence of differences in secondary
sexual traits occurs generally in allopatric populations triggered by rando
m processes and reinforced by runaway selection. In a contact zone, this ca
n "indirectly" result in assortative mating. In sympatry, cases of speciati
on by means of sexual selection are scarce unless ecological barriers are a
dduced. The conclusion is that sexual selection acts in a somewhat indirect
fashion, more by enhancing previous evolutionary directions than by initia
ting divergence.