Short answers, pulled from the story.
Reason is the capacity of consciously applying logic by drawing valid conclusions from new or existing information, with the aim of seeking truth. This ability distinguishes humans from other species and underpins activities like philosophy, religion, science, language, and mathematics.
Aristotle defined human beings as rational animals, emphasizing reason as a core characteristic of human nature. He described the highest human happiness as a life lived consistently, excellently, and completely in accordance with reason.
René Descartes explicitly rejected the traditional notion of humans as rational animals, suggesting instead they are nothing more than thinking things. He brought into doubt all knowledge except that of the mind itself in the process of thinking.
Dan Sperber and Hugo Mercier argue that other forces beyond individual benefit drove the evolution of reason. They point out that reasoning proves most effective when done as a collective, demonstrating success through projects like science.