Lines of evidence from divergent fields of biology have begun to demonstrate that evolutionary adaptation can happen with a speed that is inexplicable via random mutation of protein-coding genes. Evolution appears to happen most rapidly in regulatory RNA networks—networks that are primarily derived from transposons. Many transposons appear to be intimately involved in the evolution of both cellular and organismal stress response systems and, in turn, are regulated by stress. Further, in the organs most involved in flexible adaptation to changing environmental demands, for example, the mammalian brain, exapted transposons play a central role in the emergence of plasticity in response to experience.