A review article published in “Nature Reviews Genetics” brings together evolutionary theory, comparative genomics and large-scale human genetics to explain why we age and why ageing rates differ among individuals and species. The two authors—from the Leibniz Institute on Aging (FLI) in Jena and University College London in London—describe how, because modern humans now routinely survive into old age, we live with the late-life consequences of biological pathways that natural selection optimized for youth, and of harmful mutations that act too late in life for selection to clear them efficiently. It points to shared genetic causes and conserved therapeutic targets.