A Comparison of Primate and Dolphin Intelligence as a Metaphor for the Validity of Comparative Studies of Intelligence
Primates and cetacean have been considered by some to be extremely intelligent creatures, second only to humans. Their exalted status in the animal kingdom has lead to their involvement in many experiments which hope to gain a better understanding of the basis of human intelligence. These experiments coupled with analysis of primate and cetaceans brain structure has lead to many theories as to the development of intelligence as a trait. Although these theories seem to be sound, there is some controversy over the degree to which non-human studies can be used to infer about the structure of human intelligence.
By many of the physical methods of comparing intelligence, such as measuring the brain size to body size ratio, cetacean surpass non-human primates and even rival human beings. For example dolphins have a cerebral cortex which is about 40% larger a human being's. Their cortex is also stratified in much the same way as a humans(1). The frontal lobe of dolphins is also developed to a level comparable to humans. In addition the parietal lobe of dolphins which "makes sense of the senses" is larger than the human parietal and frontal lobes combined (1). The similarities do not end there, most cetaceans have large and well developed temporal lobes which contain sections equivalent to Broca's and Wernicke's areas in humans (1).
Another major difference between primate and cetacean brains is that the primate brain favors the motor cortex, while "the cetaceans greatly favor the sensory region (and are not very balanced at all between the two)" (1). In the final measure of brain complexity, neural density dolphins also measure up quite favorable to humans. In certain areas of the brain concerned with "emotional control, objectivity, reality orientation, humor, logically consistent abstract thought and higher creativity" dolphins have an higher ratio of neural density(1). This seems to be correlated with dolphins ability to maintain a healthy emotional state while in captivity; humans in analogous situations often don't fair as well emotionally.
Despite the complex structures discovered in the brains of dolphins, primates have been the main focus of intelligence research. One of the main reason for the focus on primates is that they seem to be so similar to humans in many ways, the most important being genetically. Besides basic genetic similarities, or perhaps because them, primates have many advanced brain structures some of which are similar to human brain structures. Most primates have and EQ the around 2.34 (2) while humans have an EQ around 7. This may seem like are large difference, but when you consider that very few species have an EQ above 1, the difference is less profound. In addition to similarities in size and structure "primates devote more of their energy resources to their brains than do most other...