What is Written on a Dog’s Face? Implications of Phenotype Diversity in Human-directed Canine Communication
Open AccessThe past ten years have seen an explosion in research into the evolutionarily unique interspecific relationship between humans and dogs, including and especially the ways in which the two species communicate with one another. Of particular interest are the behavioral, physical, neural, and genetic adaptations that domesticated dogs have acquired to be more efficient and effective social partners with humans. (Aria et al., 2021) verify canine cognitive and behavioral studies showed a steeper growth curve with respect to a “Behavioral Sciences” subject category since 2005; and that while 218 papers related to dog studies were retrieved from search parameters between 1993-2005, a search between 2006-2018 return 1307 results for a six-fold increase.These numbers would rightly suggest that researchers are responding to a more general desire for information about canine companions, and why and how they came to be the only large carnivore domesticated and living comfortably among humans. In recent decades dogs have, it would seem, entered a new era of integration into the evolving human social order, fulfilling different and expanded roles within society and the home. Dogs today function as close companions, family members, and are even considered by many as “children.” Such projections may be linked to changing family and household structures (including more single-person households), delayed childbearing, and shifting workforce dynamics (Lesthaeghe, 2014; Volsche, 2018, 2021; Volsche et al., 2022).In addition to gaining a better understanding of dogs in their own right, the growing field of canine sciences offers novel models to explore behavioral, genetic, and neural correlates of questions related to human evolution. While nonhuman primates have traditionally been favored models for investigating human origins because of their close evolutionary relatedness, there are notable incongruencies in the social and physical environments of humans and other primates. Dogs, on the other hand, have shared our immediate environmental and social niches for the entirety of their species existence, and very nearly most of ours, which has provoked a remarkable set of shared behaviors that are underscored in some cases by physiological and genetic convergence (Coelho et al., 2018; Niego & Benítez-Burraco, 2019; Song et al., 2013; vonHoldt et al., 2017).In particular, pro-sociality, a hallmark of human behavior, is likewise a defining characteristic of dogs (vonHoldt et al., 2017). In humans, our extensive communicative repertoire both stems from and results in increased pro-sociality. As it became more evolutionarily advantageous for humans to be convivial, even when interacting with non-kin, our tools for intraspecific communication multiplied (Dunbar, 2016; Stout & Chaminade, 2012; von Heiseler, 2022). With this, our capacity for complex thought processes and emotions expanded, and so too did our need for more complex forms of communication (Dunbar, 2003; Fitch et al., 2010; Heyes, 2012; Jerison, 1963). Aside from human language, chief among those tools are facial features and expressions, which not only aid in identifying conspecifics in large social groups, but significantly enhance both verbal and nonverbal social interactions (Jack & Schyns, 2015). And though facial communication may be evolutionarily conserved throughout the order and is indeed significant to other primates, species-specific facial expressions derived in humans reflect more complex thoughts and emotions, and intentionality when it comes to producing expressions, in particular, may be unique to humans (Kret et al., 2020; Parr et al., 2005; Pollick & de Waal, 2007; B. M. Waller et al., 2022).While dogs do not possess the capacity for language production, we know that they have nevertheless adapted to respond appropriately and effectively to a variety of human-favored communicative signals and cues, linguistic and otherwise. What we are still trying to determine is how they do this, that is, what factors, behavioral or otherwise, facilitate successful communication between dogs and humans? In this dissertation, I apply several methodologies to investigate a specific aspect of this query, namely, how canine facial features impact social interactions between humans and dogs. In Chapter 1, I briefly review information relevant to the discourse: 1) What we know about the process of canine domestication and its significance in fostering interspecies communication between humans and dogs; 2) Our understanding, to-date, of how, when, and perhaps why dogs attend to human faces (and humans to dog faces); and 3) The genetic basis for canine coat pigmentation. This section concludes by pointing to future directions in research, several of which I have begun to pursue herein. Chapter 2 provides a gross anatomical study of canid facial muscle morphology. In this chapter I compare facial muscles of several canid species, including domesticated dogs (C. familiaris), wolves (C. lupus), coyotes (C. latrans), red fox (V. vulpes), gray fox (U. cinereoargenteus), and Arctic fox (V. lagopus). Specifically, I evaluate the animal specimens for presence/absence of two facial muscles in the eye region previously implicated by (Kaminski et al., 2019) as significant to human-directed facial communication in dogs, the levator anguli occuli medialis (LAOM) and the retractor anguli occuli lateralis (RAOL). In this study I find that the target muscles in question are not unique to domesticated dogs, and in fact are present in several of the other specimens, with varying degrees of robustness among individuals. These findings imply the presence of the muscles is likely not directly related to interspecific communication, as has been previously suggested. Based on the findings discussed in Chapter 2, in Chapter 3 I move beyond musculature and extend investigation to potential correlations between dogs’ more superficial facial features (coloration and marking patterns), and their frequency of facial expressivity, as determined from photographic/video data (N = 103 dogs) coded to an original schematic, and video data coded according to DogFACS (Waller et al., 2013). Work from (Santana et al., 2013; 2014) shows that in social primates, facial markings impact facial expressivity during interactions with conspecifics. Here, I ask whether canine facial complexity is related to rates of expression, that is, do the patterns and markings on a dog’s face impact how expressive they are when interacting with human social partners. Through behavioral and physical phenotype analyses of domesticated dogs living in human households, I find slight thought statistically significant correlation between expression rate and facial complexity score, with lower faces producing higher behavior rates. Notably, it also seems that human companions may characterize their own dogs’ rates of expressivity with more accuracy if the dog has a “plain-er” face. This potential finding leads me to a further investigation of human perceptions of canine faces in Chapter 4, where I take a closer look at the effect of physical complexity of dog and human faces on how physically expressive unknown individuals are perceived to be by human viewers, and whether or not humans have an entrained preference for non-complexity (primate faces, especially human faces, are largely hairless (Waller et al., 2022) ). Here, human respondents (N= 312) completed a survey wherein they ranked photographs of neutral-state dog and human faces based on how expressive they imagine that individual to be. Specifically, I asked, in a neutral condition, are dogs with a more complex facial appearance perceived by unfamiliar humans as more or less expressive than those with solid-coated faces (i.e. do humans inaccurately rank them as not neutral)? In Chapter 4 I find that, while statistically significant at a very low effect, in practice facial complexity does not likely affect the expressivity rank of unknown dogs nor unknown humans. However, varying degrees of companionship with dogs and humans does impact how participants rank dog and human faces. In whole, this series of studies has both theoretical and practical implications for canine science, the broader fields of anthropology and zooanthropology, and for society at large. From a socio-cognitive perspective, the combined production, comprehension, and use of a complex linguistic system is generally accepted as a significant mark of delineation between humans and other species, including other primates (Berwick et al., 2013; Hauser et al., 2002; Terrace et al., 1979). Yet, as traditional language use and corresponding expressive communication is altered (especially by technology), we must consider whether this is, in fact, a valid marker. Countless other animals engage in complex, species-relevant forms of communication (Arbib et al., 2008; Dawkins & Krebs, 1978; Fishbein et al., 2020; Pfenning et al., 2014; Seyfarth & Cheney, 2010). Of particular interest are the communication adaptations of those that live most closely with us— dogs. Understanding how and to what degree interaction with humans impacts the development of novel modes of communication in dogs could provide valuable insight into what shaped early human culture, cognition and indeed, even language.Likewise, social and environmental influences uniquely shared by dogs and humans make dogs an ideal case study for investigating human cognitive and physical function, and, in some cases, dysfunction. Increasing understanding of how the selective pressures of domestication alter species’ physiology and behavior will aid in determining which genetic and neural markers of cognition and disease in dogs may also have implications for humans (Mazzatenta et al., 2017; McCune & Promislow, 2021; vonHoldt et al., 2017). Perhaps most importantly, this project may help support a more robust ethic of guardianship. If in fact what truly makes us human are our higher order cognitive functions, including morality, then we can and should use science to enhance the quality of life for our canine partners in evolution. In recent decades, dogs have become more and more significant to daily human life in a variety of contexts, including as companions for humans living in increasingly isolated conditions; working on explosives detection, disease detection, and even environmental conservation; and as life-saving service animals for the disabled. And yet, thousands of dogs are euthanized, or worse, every day. By gaining a fuller understanding of the ways dogs communicate, we can be better equipped to support them in the critical roles they fill within human societies.
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