Sagan contends that the emergence of myth and religion can also be attributed to the evolution of human intelligence. Additionally, the written word has allowed humans to preserve and transmit knowledge across generations, further accelerating our intellectual development. He argues that language not only allows us to communicate with one another but also serves as a tool for abstract thought and problem-solving. Sagan investigates the origins and growth of language, suggesting that it may have begun with simple vocalizations and gestures before evolving into the complex linguistic systems we have today.

The ability to communicate using language has played a crucial role in the development of human intelligence. Additionally, Sagan emphasizes the importance of social interactions and cooperation in the evolution of human intelligence, as they have allowed us to learn from one another and build upon the knowledge of our ancestors. This extended period of dependency allows for the development of complex cognitive abilities, such as language acquisition and socialization. One key factor is the prolonged childhood of humans compared to other animals. Sagan explores the factors that contributed to the development of human intelligence.

However, he also emphasizes the importance of understanding this relationship to enhance human intellectual potential. He acknowledges the complexity of determining the relationship between genetics and intelligence, as both nature (genetic inheritance) and nurture (environmental influences) shape our cognitive abilities. Sagan turns his attention to genetics, examining the role that genes play in the development of intelligence.

In humans, the neocortex is significantly larger than in other animals, which has facilitated our advanced intellectual capabilities. Finally, the neocortex, the most advanced part of the brain, is responsible for higher cognitive functions, such as language, abstract thought, and problem-solving. The limbic system, which governs emotions, emerged later and is shared by most mammals. The reptilian brain, responsible for basic survival functions, is the oldest part of the brain. These parts evolved in succession, each building on the capabilities of its predecessor. He discusses the triune brain theory, which posits that our brains are composed of three main parts: the reptilian brain, the limbic system, and the neocortex. In this section, Sagan delves into the development of the brain, tracing its evolution from simple organisms to the complex human brain we have today.

The Dragons of Eden by Carl Sagan