Goodall analyzes the many similarities—as well as crucial differences—between humans and chimps. Chimps’ brain structure is similar to that of humans, and they therefore likely have a brain similar to that of our shared ancestor. They have an ability to reason and to create and use tools. Goodall explains that tool use in itself doesn’t necessarily signify high intelligence; some bird species use twigs as tools but aren’t smarter than those who use their beaks. Goodall considers tool use significant when species can readily manipulate or redirect tools depending on the problem at hand. She reiterates that Gombe chimps use tools for many purposes. Researchers have witnessed chimps in captivity using tools like sticks, rocks, and straw for various purposes. Even when provided with tools and demonstrations, no chimp has ever figured out how to use one tool to make another. For example, a researcher modeled how to use an ax to cut sticks, but the chimps ignored the ax and used their teeth instead. Goodall considers tool making an instinct in chimps but argues that how they use tools is a learned behavior.

The author emphasizes the similarities between human and chimp body language and gestures. Both humans and chimps seek physical contact with a companion when frightened.