In the 19th and 20th centuries, science in Spain was held back by severe political instability and consequent economic underdevelopment. Despite the conditions, some important scientists and engineers emerged. The most notable were Miguel Servet, Santiago Ramón y Cajal, Narcís Monturiol, Celedonio Calatayud, Juan de la Cierva, Leonardo Torres y Quevedo, Margarita Salas and Severo Ochoa.