Another possibility is that animals have developed a language of thought. A lot of people say that animals have the ability to communicate via telepathy! However, a lot of people say that’s nonsense. What do you think?
Perhaps it is only humans that developed the need to communicate by speaking. For example, perhaps humans lost the ability to communicate via telepathy! Then they had to develop a sophisticated method of communication (language) and this in turn helped them develop their sophisticated ability to think.