Nonhuman animals and preschoolers struggle with Relational-Match-to-Sample (RMTS), a classic test of the capacity for second-order relational, analogical, and reasoning. These failures are often explained by limitations in representational or computational capacities. Drawing on recent evidence for robust spontaneous RMTS success (i.e., without error-feedback) in crows and parrots after minimal second-order training, we present five experiments with human adults consistent with the possibility that population differences sometimes instead derive from differences in inductive biases alone. Experiment 1 confirms human adults have the capacities and requisite representations to succeed spontaneously on RMTS. Experiments 2-5 utilize a modified RMTS task in which adults make relational matches only about half of the time. Experiment 3 tests whether eight trials of various MTS tasks, nonsecond-order training featured in the aforementioned comparative studies, can increase spontaneous second-order relational responding in human adults. Two of the MTS tasks (Number, Size MTS) do so, demonstrating that MTS training can, in fact, increase relational responding by changing inductive biases alone. The other MTS tasks (Identity, Color MTS) do not do so, evidence that the facilitating effect is not a result of matching involved in MTS per se. Experiments 4 and 5 test one hypothesized mechanism by which specifically Number/Size MTS tasks may have led to increased relational responding, that is, by inhibiting preexisting biases to match on shape and/or color, making relational matches relatively more likely. We close by discussing the importance of research into inductive biases to the project of understanding relational reasoning.