It has been suggested that the rapid evolution of brain gene expression might partly account for the emergence of human cognition. Using microarrays and computational analysis, Somel et al. found that the rate of divergence of developmentally expressed genes in humans was 3–5 times faster than in non-human primates, especially in the prefrontal cortex. They also found that microRNAs and their targets showed a faster rate of evolutionary change than other neuron-related genes, suggesting a potential role for microRNAs in the rapid evolution of the human cortex.