So that when there was a sudden accidental discovery by one member of the group, say the use of fire, or a particular type of tool, instead of dying out, this spread rapidly, horizontally across the population, or was transmitted vertically, down the generations.
所以当氏族的某一成员偶然 发现，火的使用， 或者某种工具的使用，这种方法将会迅速传播 而非凋零消亡，这种方法将会横向传播于氏族中， 或者代代纵向传播。