Small RNA regulators of social behaviour in eutherian mammals

Small non‐coding mi RNA appear to be vital in brain development and function by organising complex patterns of gene expression. These molecules are important for the regulation of synaptically localised mRNA s that encode proteins involved in neurotransmission and behaviour. In this issue of EMBO Reports , Lackinger et al [1][Lackinger M, 2019] demonstrate that a large cluster of mi RNA s, that emerged in placental mammals, functions as a repressor of social behaviour. This discovery has significant implications for our understanding of the brain, behaviour and in particular psychiatric syndromes, which have been shown to display alterations of these molecules.