Looking beyond shape: the DNA methylome reveals neuronal identity. Human cortical neuron types are identified by their cytosine methylation signatures. Each type of human neuron has a distinct cytosine methylation profile. Luo et al. used a newly developed single-cell methylome sequencing method to survey both mouse and human cortical neuron diversity (colored dots in distinct clusters), extending the legendary studies of neuronal morphology (background image) by Santiago Ramón y Cajal (1852-1934).