The article Is language the key to human intelligence? , written by David Premack, a psychology professor at the University of Pennsylvania, explains how humans have displayed their intelligence through language, unlike animals whose language (none) has evolved at all. Premack uses examples such as the grammar and syntax of human language and explains the uniqueness and evolution of language over time. He states that humans have six symbol systems: “two that evolved – the genetic code and spoken language – and four that we invented: written language, Arabic numerals, musical notation and laboratory notation (one choreographic coding system)”. One word he emphasizes over time is Recursion (“allows words in a sentence to be widely separated while still depending on each other”); claiming that humans learned both recursive and non-recursive grammar, while tamarin monkeys failed to learn a recursive grammar. He said the experiment could help explain why language in animals hasn't evolved over time. Premack also looked at other factors...