An ancient and unseen alien race uses a device with the appearance of a large crystalline monolith to investigate worlds across the galaxy and, if possible, to encourage the development of intelligent life. The book shows one such monolith appearing in ancient Africa, 3 million years B.C. (in the movie, 4 million years), where it inspires a starving group of hominids to develop tools. The ape-men use their tools to kill animals and eat meat, ending their starvation. They then use the tools to kill a leopard preying on them; the next day, the main ape character, Moon-Watcher, uses a club to kill the leader of a rival tribe. The book suggests that the monolith was instrumental in awakening intelligence.