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The connection between human and dog runs deep. Early signs of domestication date back to 33,000 years ago and unambiguously domesticated dogs are common in the archaeological record beginning 15,000 years ago. The pairing makes for a striking case in coevolution — no other species has been so thoroughly integrated into human society. Dogs are our sentinels and shepherds, hunting partners and cancer detectors. And more importantly, to those of us who have had dogs in our lives, they are our dearest friends.
Though in many ways we take their presence for granted, the story of this unprecedented interspecies alliance is complex. In recent decades, we have brought the full force of the scientific method to bear on the origins of our beloved companions. Insights from disciplines as diverse as psychology and archaeology, genetics and biology have filled out the pencil sketch of our shared history brushstroke by brushstroke, resulting in a portrait both surprising and familiar.
The Tenderness of Wolves
Until relatively recently, the tale of how dogs and humans came to be so intimately acquainted took the form of a parable: Early hunter-gatherers adopted wild wolf pups, abducting them from their dens or perhaps fostering them after killing their parents. Raised by humans and selectively bred over generations for docility and tractability, these lupine changelings morphed into something close to the canines we know today. Like most just-so stories, this appealing etiology has disintegrated under scrutiny.
For one, modern studies of wild wolf pups raised in captivity demonstrate that this would have almost certainly been impractical — the hardscrabble lifestyle of early humans was tough enough. Regardless of how much attention, training and affection are lavished on captive-raised wolf puppies, they remain wolves. They don’t take to training well and are in constant contest with their trainers for dominance.
“I dont know that many hunter gatherers would have had the time or patience to deal with a wolf pup and I dont know why they would want to,” says archaeologist Angela Perri of the University of Nevada, Las Vegas.
More likely, domestication happened slowly, in fits and starts. “This symbiotic or commensal relationship,” says Robert Quinlan, professor of anthropology at Washington State University, “probably initially happened accidentally.”
Wolves more likely became acclimated to humans while scavenging the remains of their kills — they essentially kicked off the domestication process themselves. “Wolves on their way to becoming dogs were a great alarm system,” Quinlan says. Domestic dogs are in fact more vigilant than wolves. The off-spring of these more-tolerant wolves were likely then selected for other useful skills, such as hunting.
The relationship may have been reinforced by the innate human attraction to pedomorphic, or infantile, features like wide eyes and shortened faces, seen in wolf puppies and exaggerated in domestic dogs, even in adulthood. An ethnographic study co-authored by Quinlan found that, contrary to the stereotyped of a man and his dog forging their way through the wilderness, women’s perceptions of dogs were positively correlated to both their utility in a given society and their status as persons. It may have been women who consolidated this millennia-long friendship.
Whatever the reasons for the initial attraction, dog domestication was not a singular event, but rather constituted a multitude of events, spaced across geography and time. And it wasn’t a one-way street.
Semi-domesticated animals frequently returned to the wild and interbred with wolves. In a vivid illustration of that fact, it was recently determined that black wolves carry a small amount of dog DNA. Others persisted in an intermediate state, as in the case of the New Guinea highland wild dog and its likely descendant, the dingo. The New Guinea highland wild dog is thought to have left mainland Asia in the company of humans and then returned to the wild before trekking across a land bridge to Australia and there evolving into the dingo.
Perri cautions that it can be nearly impossible to tell if early canine remains were dogs or wolves. “Neither their morphology nor their genetics are smoking guns when it comes to domestication,” she says.
At the end of Wilson Rawls’ 1961 classic Where the Red Fern Grows, the adolescent narrator buries his two canine companions with a solemnity all too familiar to those of us who have endured a similar loss. To cynics, this may seem like puerile anthropomorphism — romanticizing a relationship with an animal.
This dismissal, however, ignores thousands of years of similar practices. The careful interment of dogs predates even the rise of agriculture, poignantly reinforcing the strength of the bond between our species. Anthropological analysis finds that dogs have been accorded human-like burial rites for thousands of years.
“It’s ubiquitous,” says Petra Cunningham-Smith, a doctoral candidate at the University of Florida who studies the role of dogs in ancient Mesoamerica. “Dog burials are found all over the world.”
To be sure, some prehistoric pups were sent to doggy heaven in less wholesome contexts. Excavations have turned up plenty of dogs that were sacrificed in religious rituals and others that were more feast than friend, scarred with knife marks indicating slaughter for food. And some inclusions of canine remains in human burials suggest a symbolic rather than companionable relationship, with many graves including single elements such as jaw bones.
“Around 12,000 to 14,000 years ago is where we start seeing morphological and genetic differences in early remains that are so different from those of wolves that we can confidently say we’re seeing domesticated dogs,” says Perri. Skulls with shorter faces and wider eye sockets become more frequent in the archaeological record beginning in this period.
One found in Germany, the Bonn-Oberkassel dog, shows signs of physical deterioration due to advanced distemper, suggesting that it was cared for during its illness. A specimen found in a Roman burial in Tunisia, estimated to have been 18 years old at the time of its death, was severely arthritic and missing teeth, meaning that it was almost certainly a treasured pet.
Among the most poignant is a grave found in Israel containing an adult woman with her head nestled against a dog or wolf pup dating to about 12,000 years ago. If not necessarily a definitive case of domestication, the grave does indicate the growing importance of canines in human life.
In Mesoamerica, Cunningham-Smith notes, dogs served as guides to the afterlife. “There were certain requirements,” she says. “For instance, you’d have to have a yellow dog or a red dog. It couldnt be a black dog or a white dog.”
The positioning of dogs during burial and the inclusion of grave goods often mirrors the treatment of human bodies when they are interred. Dog corpses were sometimes curled up, as if sleeping. And the objects with which they were buried signified their societal value. A grave in Skateholm, Sweden included flint blades and deer antlers — also common in nearby male human graves. And Australian rock burials of dingoes, which may have been kept as pets and guard dogs, sometimes feature the same paperbark wrappings used in human mortuary preparation.
HYPOTHESIS AND THEORY article Front. Psychol., 13 September 2021 Sec. Language Sciences
Different factors seemingly account for the emergence of present-day languages in our species. Human self-domestication has been recently invoked as one important force favoring language complexity mostly via a cultural mechanism. Because our self-domestication ultimately resulted from selection for less aggressive behavior and increased prosocial behavior, any evolutionary or cultural change impacting on aggression levels is expected to have fostered this process. Here, we hypothesize about a parallel domestication of humans and dogs, and more specifically, about a positive effect of our interaction with dogs on human self-domestication, and ultimately, on aspects of language evolution, through the mechanisms involved in the control of aggression. We review evidence of diverse sort (ethological mostly, but also archeological, genetic, and physiological) supporting such an effect and propose some ways of testing our hypothesis.
Over the last decades, language evolution has emerged as a favorite topic of inquiry for researchers from different fields, from linguists to anthropologists to ethologists to prehistorians. Language is a hallmark of the human distinctive phenotype, enabling sophisticated ways of thinking, communicating information, and organizing human societies. For many years, a sharp divide was established between the evolution of the cognitive and behavioral hardware that enables us to learn and use languages (aka faculty of language, language-ready-brain, or more recently, human linguisticality) and the particular codes we use in our daily interactions (aka languages). Whereas the former was hypothesized to result from biological changes mostly (aka language evolution), present-day languages were hypothesized to derive from the first language(s) used by first anatomically modern humans (AMHs) via random modifications triggered by external factors, like social and geographical isolation or cultural exchanges (aka language change). Putting this differently, although many languages are currently spoken by human beings, they have been thought to exhibit similar core properties because these properties are imposed by our brain architecture. Chomskyan (evolutionary) linguistics is a distinct example, with its claim that language as a cognitive faculty emerged quite recently and has not undergone modification since then, whereas individual languages have changed over time, but with this change being constrained by this basic, uniform, and unaltered cognitive and behavioral framework (Bolhuis et al., 2014).
In biological sciences, niche construction theory has recently emerged as a robust theory aiming to account for these feedback loops between biology and culture. It can be thus expected to also provide a rationale for most aspects of human evolution. Under this view, our biology enables us to construct a cultural environment or niche (encompassing ways of life in a broad sense, from clothe making to food supplies strategies to transmission of know-hows) that modifies, reduces, or even eliminates many of the selective pressures most animals need to cope with and which they mostly address via biological changes. Certainly, many other animal species exhibit some form of culture that increases their survival rates in the absence of biological modifications, but in our species cultural niche construction is widespread and seemingly accounts for many crucial aspects of our distinctive phenotype (Laland et al., 2000; Kobayashi et al., 2019). Language is not an exception (Sinha, 2015).
Interestingly enough, in songbird species, domestication increases song complexity (Takahasi and Okanoya, 2010; Kagawa et al., 2012; Okanoya, 2017). This is seemingly due to the changes in the glutamate-dopamine signaling in the striatum brought about by the attenuated stress signaling under domestication, which results in more variable vocalizations (O’Rourke et al., 2021). These findings paved the way toward claims that domestication might be involved in the evolution of human language too. Although a comprehensive model of language evolution under the effects of self-domestication is still pending, some hints can be found in the recent literature. For instance, Thomas and Kirby (2018) have argued that our self-domestication fueled the processes that enable the cultural evolution of language, particularly, the transmission of communicative systems through learning, as well as the ability to infer the communicative intent associated with a signal or action. Likewise, in a series of related papers, Progovac and Benítez-Burraco (2019), Benítez-Burraco et al. (2020), and Benítez-Burraco and Progovac (2020) have hypothesized in some more detail how changes in the management of aggression as a result of our increased self-domestication might have contributed to make language structure and use more complex via its impact on behaviors needed for acquiring and mastering a language (like language learning by children, language teaching by adults, or language play), with self-domestication and language complexity being engaged in a positive feedback loop. They have also advanced a potential neurobiological mechanism accounting for this effect (see Benítez-Burraco and Progovac, 2021 for details). In brief, the same neuronal mechanism, involving a widespread connectivity between cortical and subcortical structures, is responsible for the suppression/inhibition of reactive aggression and for syntactic chunking. Consequently, as self-domestication increased, language structures and uses also became more complex. At the same time, using more complex structures would have contributed to increasing the cortical control of subcortical mechanisms involved in aggression, particularly if these early forms of language were used for expressive purposes mostly (perhaps for verbal contests), thus replacing, at least partially, physical aggression, which is more harmful. Overall, this would have resulted in a further reduction of reactive aggression that fostered our prosociality further, as well as the other hypothesized consequences of self-domestication. In other words, these authors expect language and reactive aggression to be engaged in a mutually reinforcing feedback loop, resulting in increased language complexity and increased behavioral prosociality.
Hypotheses of this sort are difficult to test, as languages leave no trace in the fossil or archeological records. To test them, we need to rely on proxies or windows to previous stages in the evolution of language (and of languages), provided that the proper bridging inferences can be postulated. One useful proxy of this sort is animal models. Recent comparative approaches to the evolution of human language have concluded that its basic building blocks are shared with other animals (although some human-specific innovations can be expected too). Additionally, it seems that other animal species have gone through a process of self-domestication, particularly bonobos (Hare et al., 2012). Accordingly, the aim of this paper is twofold. On the one hand, we wish to argue that dog domestication can be regarded a useful model of the changes that happened in human cognition and behavior under the effect of self-domestication, with a focus on our communicative abilities, particularly language. Several lines of evidence support this approach. First, contrary to other species, dogs exhibit most of the distinctive features encompassing the “domestication syndrome” (Sánchez-Villagra et al., 2016). Second, as we discuss in detail in the next section, dog domestication resulted from selection for tameness, pretty much like human self-domestication did. Third, in dogs, domestication results in the enhancement of cognitive abilities and behaviors that are crucial for language acquisition and use, like the sensibility to social cues or the ability to solve problems relying on social cues (Hernádi et al., 2012; Udell, 2015). Finally, common genetic determinants might account for the enhanced sociability associated to dog domestication and to human self-domestication. Hence, genes selected in dogs overlap with genes selected in AMHs (Theofanopoulou et al., 2017). More importantly, some chromosomal regions known to be under positive selection in dogs are associated with aspects of our distinctive social behavior, like the region deleted in Williams syndrome (WS) (vonHoldt et al., 2017). The fact that people with WS exhibit more marked features of human self-domestication (Niego and Benítez-Burraco, 2019) makes this connection more intriguing.
Nonetheless, the paper also aims to explore the more debatable possibility that human self-domestication and dog domestication were engaged in some sort of positive feedback loop and that this mutual reinforcement contributed to language evolution in some subtle, but still important, way. In truth, this is not a totally new idea. In particular, Groves (1999, p. 111) has famously claimed that “The human-dog relationship amounts to a very long-lasting symbiosis […] and intensified in the Holocene into mutual domestication. Humans domesticated dogs and dogs domesticated humans.” That said, this possibility has not been properly tested, and it has certainly not been applied to the domain of language and communication. Again, several lines of evidence support this possibility. First, although genetic analyses have dated the origins of dog domestication to around 15 kya (Freedman et al., 2014; Freedman and Wayne, 2017), dog (proto)domestication seemingly started during the Upper Paleolithic, perhaps as early as 35 kya (Galibert et al., 2011), a period when features of human self-domestication reached its peak (Cieri et al., 2014). Second, closely living and working together with a different species has been shown to reduce stress and therefore the activity of hypothalamic-pituitary-adrenal (HPA) axis, this circumstance usually resulting in enhanced sociability, or even hypersociability, which is the physiological factor that ultimately promotes all the changes associated with (self-)domestication (Jung and Pörtl, 2015). Third, and related to this, dog domestication made human social networks larger and more complex by including members of other species; this circumstance seemingly demanded enhanced tolerance to non-kin as well as extra emotional bonding, and perhaps improved mindreading too. Contact with non-kin and, ultimately, the establishment of intergroup social networks (but also the management of intergroup conflicts) have been hypothesized to account for specific types of human languages (see Benítez-Burraco and Progovac, 2020 for details), as well as for the emergence of modern use of languages, that is, modern pragmatics (Benítez-Burraco et al., 2020).
The paper is structured as follows. We first provide a brief characterization of human self-domestication vis-à-vis dog domestication, highlighting the parallels between the two processes. We then explore the effects of human-dog interactions on their respective behavioral and cognitive phenotypes, with a focus on aspects known to be affected by (self-)domestication. Finally, we focus on communication, both verbal and non-verbal, and advance some conjectures about the putative effects of this coexistence (and possibly, co-evolution) on the emergence of present-day languages.