|Abstract:||This paper derives observed universal rankings of faithfulness constraints from biases in acquisition that result from (1) frequency differences in the input and (2) imperfections in the transmission channel. Computer simulations show that in acquisition, the child's constraint rankings will more or less end up where they yield a grammar that generates the parents' language. But the ranking will diverge a bit, as a result of the said frequency differences and imperfections. Even if the parents' language has all faithfulness constraints ranked at the same height, their children will gradually rank them according to one of the universal rankings that have been proposed in the literature (e.g. licensing by cue, positional faithfulness, markedness by faithfulness). All these rankings are therefore caused automatically by a simple learning algorithm. None of the causes proposed before, all of which were based on the assumption that speakers have some sort of explicit or implicit linguistic or extralinguistic knowledge, are needed.