We prove that arbitrary homomorphisms from one of the groups $ Homeo(\ca)$, $ Homeo(\ca)^\N$, $ Aut(\Q,<)$, $ Homeo(\R)$, or $ Homeo(S^1)$ into a separable group are automatically continuous. This has consequences for the representations of these groups as discrete groups. For example, it follows, in combination with a result on V.G. Pestov, that any action of the discrete group $ Homeo_+(\R)$ by homeomorphisms on a compact metric space has a fixed point.