Anthropologist: Many people think that if human language evolved, then something like it must be present in those species most closely related to humans, such as chimpanzees. They reason that since new traits evolve gradually, something like human language, albeit cruder, must exist in some species from which humans evolved. This general line of argument may be reasonable, but it simply does not follow that chimpanzees have anything like human language, because humans did not evolve from chimpanzees. While chimpanzees are indeed closely related to humans, this is because both evolved from a common ancestor. The evolution of human language might easily have begun after the extinction of that common ancestor. Which one of the following most accurately expresses the main conclusion of the anthropologist's argument? ['The evolution of human language began after the disappearance of an extinct species from which both humans and chimpanzees evolved.', 'The assumption that something like human language must exist in some species from which humans evolved has no clearcut linguistic implications for chimpanzees.', 'The communicative systems of chimpanzees are cruder than human language.', 'Human language is a by-product of human intelligence, which chimpanzees lack.']