Dobzhansky quipped, "All species are unique, but humans are uniquest". But, what makes human unique? Judeo-Christian theology states that it is we are created in the image of God and part of that includes intelligence. Today's Science provides some clues on why we are the uniquest.
The study looked at hierachical grammars known as Phase Structure Grammars (PSG). These differ from Finite State Grammars because PSGs can insert strings inside of strings. Why this is important is shown from the following quote from Fitch and Hauser.
Rule systems capable of generating infinite sets of sequences ("grammars") are arranged in a mathematical hierarchy of increasing generative power, termed the Chomsky hierarchy. The weakest class in this hierarchy are finite state grammars (FSGs), which can be fully specified by transition probabilities between a finite number of "states" (e.g., corresponding to words or calls). Recent evidence suggests that parsing procedures at this superficial level of complexity are spontaneously available to both human infants and nonhuman primates. However, FSGs are inadequate to generate all the structures of any human language, because all languages minimally require procedures at the next level of complexity, termed phrase structure grammars. In addition to concatenating items like an FSG, a PSG can embed strings within other strings, thus creating complex hierarchical structures ("phrase structures"), and long-distance dependencies. For example, in English, the word "if" is typically followed by the word "then," but any arbitrary number of words or phrases can be inserted between them. Such constructions (and many others) demand more sophisticated parsing capabilities, including a perceptual ability to recognize these structures and an open-ended memory to store them. There is a broad consensus in linguistics and machine learning that PSGs are more powerful than FSGs and that grammars above the FSG level are, minimally, a crucial component of all human languages. Though such abilities are available to all normal humans, it is currently unknown whether parsing abilities above the FSG level are available to nonhuman animals. We used a familiarization/discrimination procedure to address this issue in cotton-top tamarins (Saguinus oedipus), a New World primate species that has previously demonstrated successful discrimination of linguistic stimuli according to rhythmic class, along with a capacity to grasp transitional probabilities and abstract rules implicit in speech stimuli.
What makes humans unique amongst primate is the ability to process these grammars. Thus, human language is truly unique and so is the abstraction allowed by such language. The review article gives other characteristics of our uniqueness:
- Voluntary Control of Sensory-Motor Systems. Vocalization is reflexive in chimpanzees but voluntary in humans.
- Second level imitation. Here is where the individual not only copies the object of the model but also the motor action. Chimpanzees can do this with training but even human infants can do this autonomously.
- Teaching. Here the direction of communication is reversed from imitationg. This is uniquely human.
- Theory of mind. Human communication is intentional. When the speaker sees a listener making an error, he corrects it. Other primates do not.
- Grammar. Human langauge is recursive while Fitch and Hauser prove that primate language is non-recursive.
- Intelligence. All other species are specialists while humans are flexible. Other species are "hard wired" to solve particular problems. Our ability to abstract allows us to solve an open-ended series of problems.
Is the ability to have a recursive grammar the key to intelligence? In part, but there appears to be more to it. Nevertheless, we are not merely advanced animals. Intelligence does indeed appear to be the sine qua non of humans. And as such we truly are made in the image of God.