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.
Tako da kada pojedini član grupe slučajno nešto otkrio, na primjer, korištenje vatre, ili nekog alata, umjesto da otkriće nestane, ono se širilo brzo, horizontalno populacijom ili vertikalno, novim naraštajima.