ABSTRACT
Prima facie, studying animals in order to learn about uniquely human traits does not seem very promising. If certain traits are really unique to our own species, they must be investigated in humans where they actually occur. While this is the only way to obtain a detailed characterization of uniquely human features, there are important questions that this approach cannot answer. First, it cannot provide fundamental information on whether a given feature actually is unique to our own species or not. In principle, one would have to test all living species before drawing such a conclusion. In practice, however, we must rest content with excluding the presence of potentially unique human features in as many species as possible-at least in those species where they are most likely to occur, i.e., in apes and to a lesser extent in monkeys. But even once a feature can confidently be labelled as one that does not occur outside the human context, detailed knowledge of its architecture, functioning, or ontogeny during childhood, derived from studies of our own species, still offers only a limited view of that feature. A comprehensive understanding also has to encompass knowledge of its evolutionary origins, e.g., information on whether we can determine evolutionary precursors, what they look like, and how they are distributed among nonhuman animals. This will inform us about which transitions took place over evolutionary time and perhaps why.
