  We discuss evidence that quasars, and more generally radio jets, may have
played an active role in the formation stage of galaxies by inducing star
formation, i.e. through positive feedback. This mechanism first proposed in the
70's has been considered as anecdotic until now, contrary to the opposite
effect that is generally put forward, the quenching of star formation in
massive galaxies to explain the galaxy bimodality, downsizing and the universal
black hole mass over bulge stellar mass ratio. This suggestion is based on the
recent discovery of an ultra-luminous infrared galaxies, i.e. an extreme
starburst, which appears to be triggered by a radio jet from the QSO
HE0450-2958 at z=0.2863, together with the finding in several systems of an
offset between molecular gas and quasars, which may be explained by the
positive feedback effect of radio jets on their local environment.
