Philosophers often like to use examples of animals to show how difficult it is to understand the representations and thoughts of creatures that lack language. Moreover, some philosophers will claim that in the absence of language, there can be no thought. If that's true we're in a very difficult bind when it comes to understanding animal thought. In fact, some would claim that the entire enterprise is bankrupt. Yet there is a long history of research on humans where tasks have been developed to figure out what humans are thinking in the absence of language, and a massive amount of work on human infants, who have yet to express their linguistic capacity. What I argue is that some of the most profound problems having to do with the human mind can only be addressed by studying animals, not humans. There are three threads to this claim. Thread number one: there are many cases where people working on humans want to claim that a particular kind or style of thought depends upon language. My argument would be that if you want to make that claim the only species you can test that hypothesis on is an animal not humans. Not human infants, who although they have yet to develop competence with language, have nonetheless evolved a brain that is suitable for language, and therefore it's not quite the appropriate test. Similarly, studies of brain-damaged patients, who don't have production or comprehension of language they have a language aphasia are also not good subjects, because they have a brain that developed with language. Therefore if you're interested in the connection between language and thought, you must test that hypothesis on species that lack language. So in our lab and in the field, along with many other scientists like Dorothy Cheney and Robert Seyfarth, as well as others, we have explored particular kinds of thought that appear to require language in organisms like non-human primates, or non-primate animals, to see whether they have those capacities, and increasingly, there are now elegant demonstrations of such representational capacities and thoughts, but without language.
Thread number two. The second reason why people studying humans must focus on studies of animals is because there are an awful lot of claims about the special nature of a particular human thought process. Debates beginning in the 1960s and 70s, and continuing into the present, focused on the special mechanisms underlying speech. People claimed that our ability to make categorical distinctions between phonemes, like ba and pa, is due to a special mechanism underlying speech. The first hit on that claim was due to an experiment that was run by Pat Kuhl. Kuhl ran experiments on chinchillas and macaques, showing that they have the same exact perceptual abilities as do humans, given the same set of stimuli. This initiated a program of research aimed at identifying whether we can make the claim that a particular mechanism is special to humans or not. The only way to really address this claim is by studying animals.
Thread number three, which is much more familiar to psychologists and neuroscientists, is the idea that certain kinds of experiments are either unethical or logistically too difficult to run on humans, but can be conducted with an animal. Although the ethical issue usually dominates this debate, it is equally important to consider how studies of animal might complement those on humans, because we may be able to do better experiments on animals, due to the level of control, types of stimuli presented, and the long term study of single individuals through time. Such long term studies of animals, such as Jane Goodall's work on chimpanzees, and Cynthia Moss' work on elephants, have provided us with a 30 year run on the lives of highly social and fascinating creatures. It would be difficult to match such studies on humans.
So there are three ways in which studies of animals impact directly upon our understanding of the human mind, and these are now coming to play a much more dominant role in both the cognitive sciences and the neurosciences.