Recently originated 'young' genes can rapidly evolve essential functions, although the underlying mechanisms are largely unclear. Ross et al. carried out phylogenetic and functional analyses to show that the Drosophila melanogaster gene Umbrea, which arose <15 million years ago through duplication of the non-essential gene heterochromatin protein 1b (HP1b), evolved novel functions that conferred essentiality. These included alterations to protein–protein interaction domains that conferred Umbrea with centromere localization and an indispensable role in chromosome segregation.