Here is a paradox: Whatever urges we humans have to declare we are special and to identify with the superhuman, these are balanced by the desire to believe animals are just like us. For millennia, arguments grounded in claims of unique relations to God, or gods, have stipulated that humans are different from animals. Against these stand pet owners extolling their charges' abilities, stories portraying animals as talking, thinking, acting, and interacting as humans do, and scientists offering evidence of remarkable feats by the animals they study. Even Furbies arouse in us a sense of commonality (Green Reference Green2007).
In the post-Darwin era, scientists try to resolve this paradox by addressing whether humans should persist in claims of uniqueness and on what basis. The authors of “Darwin's mistake” are not the first to defend “pro-difference” positions. Taking on a less formidable foe in a book titled Dr. Doolittle's Delusion, Anderson (Reference Anderson2004) argued that only humans truly have language. And I, after years of dealing with undergraduates enamored of the abilities of animals like Sarah, Koko, and Alex, who had achieved fame if not language, argued that toddlers are already distinguished by language, self-reflection, and understanding of mind (Shatz Reference Shatz1994).
Neither Anderson nor I, however, proposed anything like a “supermodule” of cognitive ability to account for the learning and organization of human language as well as other cognitive skills. Penn et al. take that courageous step, arguing both against the adequacy of earlier proposed “supermodules” and for a broader alternative, although they admit to leaving as yet unspecified how it would function in a “neurally plausible cognitive architecture” (sect. 10.1, para. 3). Nonetheless, with their proposal, they offer new grounds for human-animal disparities and an intriguing explanatory basis for human language as essentially different from animal communication systems but not wholly unique among human cognitive systems. Notwithstanding their title, they do this while agreeing with the undeniability of evolution.
Penn et al. offer evidence for their claim based largely on what animals cannot do. An even stronger case could be made with more evidence of what human toddlers can do that sets them apart so early from even our closest relatives. My “pro-difference” stance followed from close observations of a toddler who, before age 3, had revealed through his talk that he could do higher-order, relational abstract reasoning about reality and fantasy, the artistic abilities of self and other, and his own knowledge and the false beliefs of another. Donning rain boots and saying, “These are my fireman's boots” […] “I use them as my fireman's boots,” the toddler showed he could imagine something to be what it was not. Upon viewing a cat painted by an adult, he opined that the cat he had painted was “lousy.” And, after appearing naked before his grandmother and telling her he had left his pajamas in the bathroom (she had retrieved them and found them dry), he said, “You thought these were wet” (Shatz Reference Shatz1994).
Of course, children do not demonstrate higher-order cognitive capabilities like theory of mind (ToM) in every situation (Wellman Reference Wellman and Goswami2002), and this counts as evidence that such abilities develop gradually. Overall cognitive complexity of the tasks requiring such reasoning is surely one explanation for this (Andrews et al. Reference Andrews, Halford, Bunch, Bowden and Jones2003). However, cognitive complexity alone cannot account for all human-animal differences. As Penn et al. note, animal behavior can hardly be deemed cognitively simplistic. Not long ago, I had the chance to reconsider my earlier position in light of recent claims for animals; my review of the new evidence, on both corvids and children, convinced me not to change my views (Shatz Reference Shatz, Brownell and Kopp2007). Animal cognitive sophistication is not qualitatively comparable even to toddlers' rudimentary knowledge about imagination and mind.
Admittedly, much (but not all) of the evidence for early ability is based on talk, and animals cannot talk. A dog shaking his blanket between his teeth with the violence that he might use on an unfortunate squirrel may be playing symbolically; still, we have no basis for attributing to him an awareness that reality and fantasy differ. In contrast, toddlers use language to show they can think about such a difference and so much more.
Crucially, even as they are acquiring a specific language, toddlers reveal they are using higher-order relational capacities to do so. For example, they begin to organize their lexicon even before having full knowledge of specific word meanings (Shatz & Backscheider Reference Shatz and Backscheider2001). And a toddler was observed reciting to himself a series of personal pronouns, apparently organizing them into a category, although his basis for doing so remained obscure (Shatz Reference Shatz1994). The research on the distributional properties of child-directed language suggests a basis for such behavior: The input feasibly offers adequate material for category creation to an organism predisposed to create categories of items related on abstract bases (Mintz et al. Reference Mintz, Newport and Bever2002; see also Tare et al. Reference Tare, Shatz and Gilbertson2008). Additionally, experiments have shown that hierarchical organization is within the ken of toddlers (Diesendruck & Shatz Reference Diesendruck and Shatz2001; Lidz Reference Lidz, Hoff and Shatz2007). These findings show that not only is language a means to revealing higher-order human capacities, but its acquisition may indeed be the consequence of exercising those capacities, as Penn et al. argue.
Finally, it may not be surprising that animals, clever though they are, remain mired in re-description of perceptually based data. Without having the higher-order capacities to learn language, they have no means to learn from testimony (Harris Reference Harris, Carruthers, Stich and Siegal2002) or to use language to learn more (Shatz Reference Shatz1994; Reference Shatz, Brownell and Kopp2007). Much of the immense power of language stems from the ability of the language user to engage in conversations with other like-language users to obtain more material on which to exercise one's higher-level cognitive abilities. Language may not be unique as an instantiation of the capacity Penn et al. grant humans, but its use may be the one that allows humans to go ever farther in bridging domains of knowledge in new ways. Penn et al.'s proposal is wholly compatible with the idea that the most important consequence of human uniqueness is the extension beyond clever animal exploitation of perceptions to the creative, imaginative re-description of both direct and indirect experience through language itself.
