While both Neandertals and modern humans develop brains of similar size, very little is known about whether modern human and Neandertal brains may have differed in terms of their neuron production during development. Researchers from the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG) in Dresden now show that the modern human variant of the protein TKTL1, which differs by only a single amino acid from the Neandertal variant, increases one type of brain progenitor cells, called basal radial glia, in the modern human brain.