Birds have developed a unique evolutionary solution to ensure the survival of males – a powerful microRNA. This tiny gene allows male embryos to survive despite a genetic imbalance between the sexes by balancing the activity of the sex chromosomes. An international research team led by biologists from Heidelberg University and the University of Edinburgh (Scotland) has discovered this previously unknown mechanism, which differs significantly from the system that mammals have developed in the course of evolution to address the same biological challenge.