 One clan organizes the first cheela agriculture, which brings predictable food supply but provokes grumbling about the repetitive work. Shortly after, a volcano emerges in the area, and the clan invents the first sledge to carry food from more distant sources. However, within a few generations the volcano pollutes the soil. One clan leads its population on a long, arduous journey to new territory that is fertile and uninhabited. Although one genius invents mathematics to calculate and measure the band's food supply, the situation is desperate and the clan's survival depends on the self-sacrifice of the oldest members.
