  Using a chiral unitary approach for the meson--baryon interactions, we show
that two octets of J^{\pi}=1/2^- baryon states, which are degenerate in the
limit of exact SU(3) symmetry, and a singlet are generated dynamically. The
SU(3) breaking produces the splitting of the two octets, resulting in the case
of strangeness S=-1 in two poles of the scattering matrix close to the nominal
\Lambda(1405) resonance. These poles are combinations of the singlet state and
the octets. We show how actual experiments see just one effective resonance
shape, but with properties which change from one reaction to another.
