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In both the evolution of thought in the history of mankind, and the evolution of thought in an individual, there is a stage at which there is no thought followed by a subsequent stage at which there is thought.… What we lack is a satisfactory vocabulary for describing the intermediate steps.
—DONALD DAVIDSON, SUBJECTIVE, INTERSUBJECTIVE, OBJECTIVE
At least since Aristotle, human beings have wondered how they differ from other animal species. But for almost all of that time the appropriate information for making this comparison was not available—most important, because for the first several thousand years of Western civilization there were no nonhuman primates in Europe. Aristotle and Descartes could readily posit things like “only humans have reason” or “only humans have free will” because they were comparing humans to birds, rats, various domesticated animals, and the occasional fox or wolf.
In the nineteenth century nonhuman primates, including great apes, came to Europe via newly created zoological gardens. Darwin himself was dumbstruck by his encounter in 1838 with an orangutan named Jenny at the London Zoo (whom Queen Victoria termed “disagreeably human”). After publication of the Origin of Species some twenty-one years later, and the Descent of Man some twelve years after that, the differences between humans and other animals—as now represented by our closest living relatives—became much more difficult to pinpoint. Many philosophers reacted by simply defining away the problem: thinking is a process that takes place in, and only in, the medium of language, and so other animal species cannot think by definition (the most prominent modern proponents being Davidson [2001] and Brandom [1994]). Recent research on great ape cognition and thinking, such as that reviewed here, should already be undermining this “radical discontinuity” view. Great apes cognitively represent the world in abstract format, they make complex causal and intentional inferences with logical structure, and they seem to know, at least in some sense, what they are doing while they are doing it. Although this may not be fully human thinking, for sure it has some key components.
But the problem is deeper than finding a line of demarcation. The point is that the great ape species alive today are arbitrarily far from humans; it is just a matter of who survived and who did not. So what if we discovered, in some remote jungle, surviving members of the species Homo heidelbergensis or Homo neanderthalensis? How would we decide whether they possess fully human thinking—yes or no—given that, in all probability, they would be somewhere in between contemporary humans and great apes? Even more radical, what if we discovered some earlier side branches from the human evolutionary tree who had their own ways of doing and thinking about things, overlapping only partially with modern human thinking? Perhaps these creatures never developed pointing and so did not evolve skills of recursive inferring. Or perhaps they never imitated at a level sufficient for pantomime and so did not symbolize their experience for others gesturally. Or perhaps they collaborated but did not care about others’ evaluations and so did not become socially normative. Or perhaps they never had situations in which they had to make group decisions and so never came to offer one another reasons and justifications for their assertions. Our question is what would these creatures’ version of thinking look like if it skipped a key ingredient (along with all of its cascading effects) of the modern human version? We might end up with something sharing many features with modern human thinking but having its own unique features as well. The point is that, considered evolutionarily, human thinking is not a monolith but a motley—and it could have turned out other than it did.
What we have done in the current natural history is to imagine one possible “missing link” in the evolution of human thinking from great apes to modern humans based on selected aspects of the way of life of contemporary hunter-gatherers and selected aspects of the thinking of young children (accompanied by a few, admittedly indeterminant, paleoanthropological facts). But, importantly, our claim is not just that such an intermediate step can be imagined and that it probably occurred, but that it was necessary. It was necessary because one cannot even imagine going directly from ape-like competitive interactions and imperative communication to modern human culture and language with no evolutionary intermediary. Human culture and language are simply conventionalizations of existing social interactions, and to provide the appropriate raw material, these interactions had to have been already highly cooperative. Put in terms of our two historical strands, we cannot get to processes of culture and language (as invoked by Vygotsky and other culture theorists) without some kind of already existing and already cooperative social infrastructure (as described by Mead, Wittgenstein, and other social infrastructure theorists). We thus need our middle step—we would be very happy with multiple middle steps, if ours could be broken down further—to prepare the way for culture and language and all of their uniquely powerful structuring of human thinking. This intermediate step does not solve Davidson’s (1982) problem of a common theoretical vocabulary that spans from “no thought” to “thought,” but it does narrow the distance to be traversed by any one step significantly.
In any case, no matter the precise number of steps, our account presupposes that to understand uniquely human thinking we must situate it in its evolutionary context. Wittgenstein (1955, no. 132) says about language that “the confusions which occupy us arise when language is like an engine idling, not when it is doing its work.” It seems to us that many of the perplexities of human thinking pointed out by philosophers arise precisely when we attempt to understand it in the abstract, outside of its functioning in solving adaptive problems. It is natural to do this in the contemporary world because so much contemporary thinking is, in some sense, idling. But uniquely human thinking was almost certainly selected evolutionarily for its role in organizing and regulating adaptive actions, and so to understand it fully we must identify the relevant problems. If creatures from outer space came across a complex human artifact such as a traffic light, idling, they could dissect it and analyze its structure forever and not understand why it behaves in the way that it does. The wires and lights by themselves could never reveal (not even with the help of an fMRI) why the red light on one side activates only when the green light on the other side activates. To understand these actions, we must first understand traffic and how the traffic light was designed to solve the specific problems created by traffic. In the case of biological structures—and this is a central lesson of evolutionary psychology, of course—there is the additional possibility that they evolved to serve one set of functions at an earlier time, and now they serve a different set. In any case, the current proposal is that to understand the way that contemporary humans think, we must understand how human thinking evolved to meet the specific evolutionary challenges that early and modern humans faced as they moved toward ever more cooperative ways of making a living.
It is certain that some parts of our evolutionary story are incomplete. The main problem is that collaboration, communication, and thinking do not fossilize, and so we will always be in a position of speculation about such behavioral phenomena, as well as the specific events that were critical to their evolution. Most crucial, we do not know how much contemporary great apes have changed from their common ancestor with humans because there are basically no relevant fossils from this era. Furthermore, our intermediary step of early humans very likely had much more of a gradual evolution than described here; indeed, it is not even clear that Homo heidelbergensis was a separate species at all. And we have given only cursory attention to humans after agriculture and all of the complexities arising from the intermixing of cultural groups, from literacy and numeracy, and from institutions such as science and government. And so our attempt is less of an explicitly historical exercise than an attempt to carve nature at some of its most important joints, specifically, at some of its most important evolutionary joints.
A list of open questions at this point would be quite long. But two particularly big ones are these: First is the nature of the jointness or collectivity or “we-ness” that characterizes all forms of shared intentionality. Many theorists subscribe to something like an irreducibility thesis (e.g., Gallotti, 2012) in which such things as joint attention and shared conventions are irreducibly social phenomena, and attempting to capture them in terms of the individuals involved, and what is going on in their individual heads, is doomed to failure. Our view is that shared intentionality is indeed an irreducibly social phenomena in the moment—joint attention only exists when two or more individuals are interacting, for example—but at the same time we may ask the evolutionary or developmental question of what does the individual bring to the interaction that enables her to engage in joint attention in a way that other apes and younger children cannot. And so for us this means that something like recursive mind-reading or inferring—still not adequately characterized, and in most instances fully implicit—has to be a part of the story of shared intentionality. From the individual’s point of view, shared intentionality is simply experienced as a sharing, but its underlying structure, reflecting its evolution, is that each participant in an interaction can potentially take the perspective of others taking her perspective taking their perspective, and so forth for at least a few levels. But this, as they say, is a point on which reasonable people may disagree.
A second open question is how and why modern humans reify and objectify what are essentially socially created entities. Money is not just a piece of paper but legal tender, and Barack Obama is not just a person living in a large white house but commander in chief—because we act and talk as if they are these things. We also reify such things as morality, arguing not about the moral norms of different social groups, including those shared by all human groups, but rather about what is the “right” and “wrong” way to do things, where right and wrong are considered objective features of the world. And nowhere is this tendency stronger than in language, where everyone has a tendency—correctable but only with much effort—to reify the conceptualizations codified in our own natural language. About all of these things, we are like the young child who says that even if long ago everyone agreed to call the striped feline in front of us a “gazzer,” it would not be right to do so because, well, “It’s a tiger.” Our own view is that such objectifying tendencies could come only from the kind of agent-neutral, group-minded perspective that imagines things from the view of any one of us, the view of any rational person, the view from nowhere, in the context of a world of social and institutional realities that antedate our own existence and that speak with an authority larger than us. This is the authoritative voice that lies behind the use of genericized linguistic expressions in norm enforcement (“That is wrong”) and pedagogy (“It works like this”), and it determines, in large part, what we consider real. But, again, this is a point on which reasonable people may disagree.
Despite these gaping questions, and others, we cannot conceive any comprehensive theory of the origins of uniquely human thinking that is not fundamentally social in character. To be as clear as possible: we are not claiming that all aspects of human thinking are socially constituted, only the species-unique aspects. It is an empirical fact that the social interaction and organization of great apes and humans are hugely different, with humans being much more cooperative in every way. We find it difficult in the extreme to believe that this is unrelated to the huge differences in cognition and thinking that also separate great apes from humans, especially when we focus on the details. What nonsocial theory can explain such things as cultural institutions, perspectival and conventional conceptualizations in natural languages, recursive and rational reasoning, objective perspectives, social norms and normative self-governance, and on and on? These are all coordinative phenomena through and through, and it is almost inconceivable that they arose evolutionarily from some nonsocial source. Something like the shared intentionality hypothesis just must be true.