Among the open questions in light hadron physics is the nature of the light scalar mesons. Their properties are at odds with the quark-antiquark assignment, which has supported their interpretation as possible tetraquark candidates. We have tested the tetraquark interpretation in the Dyson-Schwinger/Bethe-Salpeter approach. We solve a genuine four-body equation where quarks interact by gluon exchange. This is based on previous studies of mesons and baryons which I will briefly review. For the tetraquark we find a light scalar-isoscalar state at $m \simeq 400 \; \mathrm{MeV}$. However, it does not behave like a diquark-antidiquark system but rather like a 'meson molecule'. The four-quark equation dynamically generates pion poles in the tetraquark amplitude, which strongly influence its structure and produce a physical threshold. This suggests that the $\sigma/f_0(500)$ is indeed a four-quark state, but it is dominated by pion-pion components whereas diquarks are almost irrelevant. The masses of the multiplet members $\kappa$ and $a_0/f_0$ follow an analogous pattern.