The cerebral cortex is densely packed with different nerve cells that enable us to perceive, think and act. Yet how these cell types arise while the brain develops is still not fully understood. Irene Varela-Martínez, a postdoctoral researcher at the Institute of Science and Technology Austria (ISTA), traces their origins like a family-tree detective of nerve cells. Her new study, now published in Science Advances, shows that precursor cells of neurons, contrary to previous assumptions, split early into two independent lineages and thereby give rise to types of neurons.