The Haenyeo, a group of all-female divers from the Korean island of Jeju, are renowned for their ability to dive in frigid waters without the aid of breathing equipment — even while pregnant. A study shows that the divers’ remarkable abilities are due to both training and genetic adaptation, including gene variants associated with cold tolerance and decreased blood pressure. The divers also showed pronounced bradycardia, or slowing of the heart rate, when they dived, but this trait is likely due to a lifetime of training, not genetics.