I have been meaning to write an elaboration and comment response to my post on animal intelligence, but I kept putting it off for some reason. I think the main reason is because I find it to actually be a fairly daunting subject. There is a lot of nuance to it, as well as a lot of competing preconceptions and wildly differing interpretations by a lot of highly intelligent people. This makes it difficult to get a handle on the subject, but I think it is time I stop putting it off and give my attempt.
To start off with, I would like to briefly come to the defense of Noam Chomsky. Robert first brought him up saying that he "claims that humans are the only species that have the ability for language". Regan then adds his own comment in which he disparages Chomsky with a parting shot. While I think both Robert and Regan have the correct sentiment, I think there is a subtlety to Chomsky's claims that is being missed, thereby translating his claims into the territory in which they deserve the given disparagement. In the nature of full disclosure, I have not actually read a lot of Chomsky's work on linguistics, so much of my argument here will actually be based on Steven Pinker's book The Language Instinct. Throughout the book, Pinker draws heavily upon Chomsky's work and ideas, which is why I feel comfortable weighing in on Chomsky's defense. The thing is, as I understand it, Chomsky did not make the blanket claim that humans are the only species with the ability for language, but rather that we are the only species with a generative grammar based on an innate universal grammar. While I still think the statement that humans are the only species with this ability is still overly strong (there is evidence that some species of monkey are capable of a limited form of generative grammar, and our investigations into the cognitive abilities of other animals are far from complete), Chomsky's ideas are much more defensible than the patently false claim that humans are the only species with linguistic abilities (something which Regan rightly pointed out should immediately be rejected by anyone who has ever had a dog). Essentially, I think Chomsky is correct in pointing to our propensity for complex communication as one of the major cognitive advantages we have (though, like I said, I would modify his statements from we are the only species with these abilities to perhaps we are the most successful at utilizing them - much like one would correctly say a cheetah is the fastest land mammal instead of incorrectly saying the cheetah is the only land mammal to have mastered sprinting), but I do not necessarily agree with him on many of the subtler aspects of his analysis.
Speaking of unique cognitive abilities, this leads me to the apt question posed by jbrydle of whether or not our brains are fundamentally different from the brains of other creatures. The answer to this question is not straightforward, but my answer is that essentially we do not know for sure. I would now like to qualify that statement of ignorance with an extensive ramble of conjecture based on what we do know, and explain why that leads us to a state of ignorance. To start with, I would like to propose as an analogy the human hand. In plain appearance, we are capable of easily differentiating between a human hand and those of other species. However, in terms of function and arrangement, making the precise distinction becomes much harder. We are certainly not the only primate species with opposable thumbs, nor are primates the only mammalian species capable of gripping and manipulating objects with their hands (beavers, squirrels, and many other rodents have quite dextrous front paws). Likewise, elephants have adapted their noses rather than hands to the fine manipulation of objects, with the appendages on the end of their trunks capable of many of the same abilities as people. Outside of mammals, most birds have an opposable digit on their feet which allows them to manipulate and grip objects. Of course, this is quite a cursory and shallow view of the gross properties of the hand, but my point is that even something as basic and highly visible as the hand does not have a simple answer to what makes the hand of one species unique from others, especially when one is focusing on functional abilities rather than simple physical dimensions.
Moving from the hand to the immensely more complicated brain, therefore, one can see how the question is easily bogged down by nuance and qualifications. When one looks at the gross anatomy of the brain, the human brain does tend to have a more wrinkled outer exterior, known as the neocortex, than most other mammals (this increases the surface area of the cortex, since the functional setup of the cortex is a thin set of cellular layers. There are other anatomical differences as well, but I am going to try to avoid making this post into one long rendition of specific anatomical details). The neocortex is usually just referred to as the cortex, but there is more than one area of cortex in the brain as there is also a cerebellar cortex forming the outer layer of the cerebellum, which I have discussed in some detail before, so the neocortex is the term used to specifically speak about the more recently evolved cortical regions that comprise the outer shell of the cerebrum. It is also sometimes called the cerebral cortex, and it is only found in mammals. In non-mammals with advanced cognitive abilities (like many birds), quite different neural structures have evolved, often through the extension of primitive structures shared with our own brain. An example of this is in the different forms of visual perception between birds and mammals. In primates, most of our visual processing takes place in the visual cortex of the occipital lobe (the lobe at the back of one's head). There is also small midbrain structure called the superior colliculus (it is kind of like a little knob on the anterior dorsal surface of the midbrain), however, which plays an important role in visual perception. The superior colliculus provides a map of the visual field and is primarily used in spatial navigation. Its existence in the human brain allows for a condition known as type one blindsight, in which damage to a person's visual cortex has left them consciously blind. They are often, however, capable of fairly competent spatial navigation (such as walking through a room with scattered furniture without a large number of collisions) due to their superior colliculus. One interesting side-note to this condition is that because of the loss of cortical visual processing, a person suffering from blindsight is no longer consciously aware of the presence of light in their environment. Therefore, while they will be able to navigate an environment with the lights on, if you turn the lights off and ask them to walk back through the room, they will be unable to avoid collisions in the same manner (and will be rather confused about why they are suddenly having a much greater degree of difficulty).
Why am I focusing so much on the superior colliculus? Because in non-mammals it is called the optic tectum and it is particularly well developed in several predatory bird species such as owls, eagles, and hawks. Researchers have found, for example, that crows can visually differentiate between specific individuals among both crows and people. The ability to visually distinguish individuals is quite a complex task, and requires far more visual processing than that available in the standard mammalian superior colliculus. Thus, this rather long-winded example illustrates the first of many difficulties for anyone trying to definitively differentiate between the cognitive abilities of species. Because the brain is essentially a computational device providing behavioural control for an animal based on the interaction of its neurons, many different architectures can yield similar computational power. Thus, even if we have evolved novel cognitive abilities beyond those of our other ape relatives, it is extremely hard to definitively say whether or not those same abilities have independently evolved in other species.
This has grown quite long already, so I think I might stop it here. Hopefully this provides at least a little bit of explanation and feedback for the comments to my earlier post, as well as prompts some more thought and input on the subject.