Stem cell researchers at the Lund University, Germany, identify ZNF558, a transcription factor expressed in human but not chimpanzee forebrain progenitors cells, that regulates mitochondrial function and determines the timing of early human brain development. The authors show this transcription factor regulates a gene called SPATA18 that regulates the selective degradation of mitochondria. The expression of ZNF558 is controlled by the size of a structural repeat in noncoding DNA that is longer in chimpanzees than in humans. The study provides evidence of a role for DNA structural variations in human brain evolution and may contribute to genetics-based answers to questions about psychiatric disorders that are unique to humans.