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Part I
The evolution of the social mind
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1
The (r)evolution of primate cognition
Does the social intelligence hypothesis lead us around in anthropocentric circles?
Louise Barrett
Introduction: anthropomorphic reflexivity
The British comedian, Eddie Izzard, has a joke about squirrels: isnât it weird, he says, the way they pause suddenly while eating, like theyâve just remembered something terrible? Izzard mimics a squirrel eating a nut before pausing dramatically and asking himself: âDid I leave the gas on?â There is a pause for laughter, before Izzard resumes his imaginary nut-eating, saying dismissively: âNah ⌠of course I didnât!! Iâm a f**king Squirrel!â As well as getting an even bigger laugh, the notion of a squirrel anthropomorphically commenting on the folly of attributing an anthropomorphic thought to a squirrel captures the reflexivity of human thoughts and action, adding a further layer to the joke. For anyone interested in recent developments in comparative cognition, yet another layer is added by the recognition that this same reflexive quality structures much of the debate over the use of anthropomorphism as a scientific strategy, with worries raised over whether ascribing particular traits to other species, or our refusal to do so, is a reflexive response to the way in which we wish to see ourselves.
What makes this all even more mind-bending is that human reflexivity is itself argued to have arisen evolutionarily (and ontogenetically) as a result of the intense sociality that characterizes our species: Dewey, Mead and Vygotsky, for example, all suggested that human selves, and our ability to see our selves as selves, arose from the internalization of those around us to produce a âgeneralizedâ or âsocial otherâ (Dewey 1958; Mead 1934; Vygotsky 1997). In this view, sociality is fundamental to our individuality, representing both its source and cause. Similar ideas about the evolutionary pressures generated by social life have also been put forward to explain the evolution of cognitive abilities across the primate order as a whole (Humphrey 1976; Dunbar 1998). In particular, the social intelligence hypothesis or, as it is now more commonly known, the social brain hypothesis has enjoyed great success as an explanation for why the anthropoid monkeys and apes, including humans, should possess the largest brains for their body size across the animal kingdom.
In what follows, I briefly trace the history of the social intelligence hypothesis, highlighting its strengths and weaknesses as a general theory of cognitive evolution. I then go on to consider how the social intelligence hypothesis links to current debates on anthropomorphism in ways that preserve the essential anthropocentrism that lies at the heart of both. As a parting shot, I suggest that this outcome is inevitable if we accept the social intelligence hypothesis as our best explanation for primate cognitive evolution, which perhaps explains why we continue to find ourselves in the same mind-bending zone as Izzardâs forgetful squirrel.
A brief history of the social intelligence hypothesis
Following Alison Jollyâs early suggestion that primate social life âpreceded the growth of primate intelligence, made it possible, and determined its natureâ (Jolly 1966, p. 506), Humphrey (1976) subsequently (and independently) made a similar claim based on his own observations of captive monkeys and wild apes. As he pointed out, the mountain gorilla, which lives, effectively, in a giant bowl of salad, faces a set of ecological problems that are simple and finite, and no more demanding of intelligence than those that apparently face other, less brainy, creatures. Add in the demands of social life, however, and you have a game-changer: obligate sociality places a premium on the ability to predict how other animals are likely to act, a capacity that makes it possible to anticipate, ameliorate or avoid altogether the competition that arises when animals are forced to live together and share resources. In other words, animate beings, with agendas and goals of their own, generated the selection pressure to acquire a specific kind of psychological insight into others, and a more âcreativeâ form of intelligence; one that is fundamentally different from the practical knowledge needed to forage effectively and efficiently.
More specifically, Humphrey (1976) made the case for primates as âsocial gamesmenâ (p. 309), rather like human chess-players: they needed to both preserve the overall structure of the group while âexploiting and out-manoeuvring othersâ (p. 309). The idea of primates as âcalculating beingsâ capable of a âspecial form of forward planningâ (p. 309) gained even greater prominence with the publication of the âMachiavellian Intelligenceâ (Byrne & Whiten 1989). As the editors were at pains to note, the word âMachiavellianâ referred only to the need for a specifically psychological understanding of others, rather than the need for manipulativeness or deception, although these clearly formed part of the argument, and were especially prominent in Humphreyâs work.
Empirical tests of the theory then followed, presenting evidence to suggest that social factors had indeed been more important than ecological factors in promoting brain size evolution: Dunbar (1992, 1995) found a positive correlation between neocortex ratio and group size across the anthropoid primates, while simultaneously demonstrating that ecological factors did not show any significant relationship. This was interpreted as showing that primates used specifically social strategies to help cope with the ecological problems they faced (e.g., competition for food resources); problems that, in turn, had been generated by selection pressures favouring group living (most specifically, avoiding predation: van Schaik 1983).1 Further studies reinforced the association between social life and brain size, by correlating neocortex measures with complex social behaviours like promiscuous mating (Pawlowski et al. 1998), grooming clique size (Kudo & Dunbar 2001) and rates of deception (Byrne & Corp 2004). This led to the further claim that, much as Humphrey (1976) had argued previously, it was the ability to represent and manipulate specific kinds of information about social relationships (as opposed to, say, improved memory capacities) that both selected for increased brain size, and then placed limits on the size of group that a given species was able to sustain. More specifically, the form of social intelligence indexed by enlarged brain size âprincipally focuses on the ability to use knowledge about other individualsâ behavior â and perhaps mind-states â to predict and manipulate those individualsâ behaviorâ (Dunbar 2003, p. 167). What was noticeable in this shift to empirical investigation, then, were the assumptions that large neocortex size supported a highly specific kind of cognitive ability, and that group size could be used as an appropriate indicator of social complexity, without all that much in the way of independent empirical support for either of these positions.
In recent years, this has led some researchers to question whether evolutionary size increases in particular parts of the brain can, in fact, be traced causally to sociality in the manner implied (Healy & Rowe 2007; Healy & Rowe 2013; Rowe & Healy 2014). The rather nebulous concept of social complexity used in these analyses may also explain why, when empirical work was extended to other species,2 the nature of the relationship proved to be distinctively different to that of the primates, with pair-bonding (i.e., the formation of an enduring relationship between adult mates) emerging as the key correlate of enlarged brain size (Dunbar & Shultz 2007; Shultz & Dunbar 2007). This naturally required some reconfiguring of the original hypotheses, with a more precise delineation of the quantitative versus qualitative demands of sociality. Among the primates, the use of both a quantitative measure of group size and relative neocortex size rested on the assumption that tracking a large number of dyadic relationships generated a significant cognitive burden. As described above, this quantitative demand was accompanied by the (implicit) assumption that animals also possessed a conceptual understanding and recognition of relationship quality, and attempted to manipulate others using this information accordingly (Dunbar 1998). The discovery that pair-bonded species have the largest relative brain sizes in ungulates and birds has therefore been taken to indicate that it is primarily the quality of relationships, and not their quantity, that is evolutionarily important, thus reversing the original interpretation (Dunbar & Shultz 2007; Shultz & Dunbar 2007; see also Dunbar & Shultz 2010).
The aspect of social life now considered to have selected for the enhanced brain size of the anthropoid primates compared to other species is the manner in which the pair bond has been generalized to include all group members. Dunbar (2009, p. 564) characterizes this as âan important phase transition in the form of the social brain effectâ that took place at an early stage of primate evolution. The question that arises from all this is: why are pair-bonded relationships so cognitively demanding? Dunbar (2009) suggests this question has no ready answer because we also lack a ready answer to the prior question of how animals go about the day to day business of maintaining a pair bond; so far, we have only considered their value in an evolutionary-functional sense and not from a proximate-psychological/physiological perspective (i.e., we consider only the way in which they contribute to fitness, and not how they are maintained within the context of an individual lifetime).
This may well be true, but it is equally true to say that this applies to the original social brain hypothesis. The cognitive demands of social life were based on a series of assumptions, put forward by Humphrey and elaborated on by Dunbar and colleagues, that social life was complex because it required the manipulation of social information about various third-party relationships, and a form of prospective knowledge about oneâs own relationships and those of others. This, however, stemmed from the existing knowledge that the anthropoid primates had larger brain sizes than expected for their body sizes, and that they were all intensely social. The reasoning therefore ran from the observation of large brains to the kinds of complex processing large brains would afford in a social context (which, one could argue, were based largely on a folk psychological projection of our own abilities in this domain). No convincing evidence was offered to suggest that the social life of non-human primates actively required the use of flexible, highly cognitive, prospective strategies in real-time. Evidence in support of the evolutionary argument, such as the correlation between group size and brain size across the primate order (Dunbar 1995), was then taken as implicit support for the postulated proximate behavioural and cognitive mechanisms by which individual animals increased their survival and reproductive success.
Part of the reason for this seems to lie in the anthropocentric focus of the original theory, where explaining the evolutionary origin of our own extraordinarily large brains was integral to the whole project. Questions about other primatesâ social cognition were posed in ways that privileged the evolutionary origins of cognitive abilities like language, analogical reasoning and theory of mind skills, because these were seen as essential and fundamental to understanding how people are able to predict what other people will do, despite evidence that suggests that can be achieved without the need to model the mental states of others (e.g., Hutto 2004; Gallagher 2001; Andrews 2007a). Research efforts were (and still are) geared explicitly to detecting these abilities or, more commonly, their precursors, in monkeys and apes, either to reinforce our own uniqueness or to identify how our own skills in these domains have been derived from evolutionarily simpler mechanisms (e.g. Dunbar 2003; Bergman et al. 2003; Call & Tomasello 2008; ZuberbĂźhler 2000; Cheney & Seyfarth 2005; Seyfarth & Cheney 2013).
This criticism doesnât apply to all theories of human cognitive evolution, where the focus is more squarely placed on identifying the unique path taken following the evolution of our own species, rather than tracing our capacities through our common ancestors as such. Sterelny (2003, 2007, 2012), for example, argues that we are âcreatures of feedbackâ, where our uniqueness lies in the nature of the feedback mechanisms that connect, among other things, the cultural environments we construct and inhabit, human social learning, individual expertise and human life history processes. As he notes: â[a]s hominids made their own worlds, they indirectly made themselvesâ (Sterelny 2003, p. 17). Heyes (2012) makes a somewhat similar argument when she suggests that both the âgrist and millsâ of our lives â the knowledge and know-how needed to deal with the world, and the social learning processes that allow us to acquire this know-how, respectively â are both culturally inherited, in contrast to views which suggest these social learning âmillsâ are biologically inherited: according to Heyes (2012), our social learning mechanisms are cultural adaptations, not evolved functional specializations. Equally, Tomaselloâs âVygotskian intelligence hypothesisâ (Moll & Tomasello 2007; Tomasello & Moll 2010) posits unique motivations and cognitive skills that allow humans to understand others as cooperative agents with whom one can share collaborative actions (âshared intentionalityâ), an ability apparently not found in other apes. In his work on ape intelligence, however, Tomasello (Tomasello & Call 2006; Call & Tomasello 2008; Schmelz et al. 2011) does seem to offer a largely anthropocentric âtop downâ view, where apes are compared and contrasted with those of humans, with respect to capacities like the attribution of certain kinds of mental states.
This same âtop downâ view, where our own capacities colour theories of what we should look for in other species, can be seen in the hypotheses put forward to explain why pair-bonding should generate high cognitive demand. As Dunbar (2009) sees it, there are two options: (i) intense pressure for finely-tuned mate choice competences and (ii) the need to coordinate and synchronize behaviour. These are not mutually exclusive, but a âcritical testsâ analysis pitting the predictions of the hypotheses against one another is argued to come down in favour of behavioural coordination. One reason for this, Dunbar (2009) suggests, is the need for individuals to anticipate their mateâs needs so as to ensure that both members of the pair are able to meet their nutritional and other requirements. He then goes on to say:
Being attentive to the mateâs needs so as to ensure that he/she can achieve his/her daily nutrient intake has many of the hallmarks that would be recognized as theory of mind in humans. In effect, pairbonded species have to be able to engage in perspective-taking, a phenomenon that is widely accepted as being a prerequisite for mentalizing (or theory of mind: Hare et al. 2001, 2006). Hence, pair bonded monogamy can perhaps be seen as laying the foundations for the kinds of advanced social cognition found (albeit in limited form) in primates and (perhaps uniquely in full-blown form) in humans.
(Dunbar 2009, p. 568)
This has, in turn, led to the search for such perspective-taking skills on the part of pair-bonded species, with at least one study on Eurasian jays reporting positive evidence (Ostojic´ et al. 2013) (although this conclusion is contingent on the precise way in which the data were analyzed3). There is also evidence to suggest that behavioural coordination is important to breeding success: zebra finches (which are not, it should be noted, particularly large brained) that were allowed to choose their own mates displayed higher fitness and better behavioural coordination than âforcedâ pairs placed together by the experimenters (Ihle et al. 2015). In contrast, a study on New Caledonian crows demonstrated that tasks involving behavioural coordination can be learned readily and rapidl...
