The question of what makes modern humans unique has long been a driving force for researchers. Comparisons with our closest relatives, the Neanderthals, therefore provide fascinating insights. The increase in brain size, and in neuron production during brain development, are considered to be major factors for the increased cognitive abilities that occurred during human evolution. However, while both Neanderthals and modern humans develop brains of similar size, very little is known about whether modern human and Neanderthal brains may have differed in terms of their neuron production during development. Researchers now show that the modern human variant of the protein TKTL1, which differs by only a single amino acid from the Neanderthal variant, increases one type of brain progenitor cells, called basal radial glia, in the modern human brain.