Note (return) — Chapter XVII

As a tabu the geis had a large place in Irish life, and was probably known to other branches of the Celts.881 It followed the general course of tabu wherever found. Sometimes it was imposed before birth, or it was hereditary, or connected with totemism. Legends, however, often arose giving a different explanation to geasa, long after the customs in which they originated had been forgotten. It was one of Diarmaid's geasa not to hunt the boar of Ben Gulban, and this was probably totemic in origin. But legend told how his father killed a child, the corpse being changed into a boar by the child's father, who said its span of life would be the same as Diarmaid's, and that he would be slain by it. Oengus put geasa on Diarmaid not to hunt it, but at Fionn's desire he broke these, and was killed.882 Other geasa—those of Cúchulainn not to eat dog's flesh, and of Conaire never to chase birds—also point to totemism.