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Is dog domestication due to epigenetic modulation in brain?

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Abstract

Dogs (Canis lupus familiaris), derived from wolves (Canis lupus), are known as the first domesticated animal and dogs have been living in human environment for about 25.000 years. Today researchers tend to proclaim a self-domestication-process, but they are still figuring out, why and how this process started. During the Palaeolithic period, humans and wolves lived in similar structured family clans as cooperative hunters in the same ecological niche. Evolutionary continuity of mammalian brains enabled humans and wolves interspecific communication and social interaction which reduced stress and aggression during their frequently contacts as the first step of a natural domestication process. Domestication means decreased aggression and decreased flight distance concerning to humans. Therefore changes of the activity of the Hypothalamic-pituitary-adrenal (HPA) axis are suspected to be important during the domestication processes from wolf to dog. The hypothesis of Active Social Domestication (ASD) considers genetic selection as a necessary prediction but not a sufficient explanation of dog domestication. In addition dog domestication is suggested to be essentially an epigenetic based process that changes the interactions of the HPAaxis and the 5-Hydroxytryptamine (5-HT) system. The limbic brain regions such as hippocampus and amygdala play a key role in the mood control. They are sensitive to glucocorticoids and innerved by serotonergic projections. The HPAaxis and the 5-HT system are closely cross-regulated under physiological conditions. The activity of the HPAaxis is influenced thru an enhancement of the corpus amygdala and an inhibition thru the hippocampus. Hippocampal glucocorticoid receptor density (hGCR) is likely to affect its inhibitory effect on this system. Pro-social behaviour enhances epigenetically hGCR expression via increased serotonin and subsequently increased nerve growth factor levels binding on GRexon1;7promotorbloc inducing its demethylation and thus leading to decreased cortisol levels. Low cortisol levels increase social learning capability and promote the activity of the prefrontal cortex contributing to better executive function including better cognitive inhibition. Thus epigenetically decreased cortisol levels of less stressed human-associated wolf clans allowed them to extend their social skills to interactions with humans. Over time tame wolves could grow into domestic dogs able to emerge human directed behaviour.

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... Domestication includes decreased aggression and decreased flight distance concerning to humans (Benecke, 1994;Hare et al., 2012). Thus, a decrease of HPAaxis activity is fundamental in dog's domestication process (Pörtl & Jung, 2017). Regulation of HPAaxis is inherited epigenetically and thus operates very quickly during evolution (Pörtl & Jung, 2017;Ahmed et al., 2014;Trut et al., 2009;Buschdorf & Meaney, 2015). ...
... Thus, a decrease of HPAaxis activity is fundamental in dog's domestication process (Pörtl & Jung, 2017). Regulation of HPAaxis is inherited epigenetically and thus operates very quickly during evolution (Pörtl & Jung, 2017;Ahmed et al., 2014;Trut et al., 2009;Buschdorf & Meaney, 2015). Due to increased interspecific pro-social contacts between wolves and humans epigenetically based down regulation of HPAaxis promoted better executive functions and improved social learning capability in both species (Miklosi et al., 2003;Hare et al., 2005). ...
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In the debate on canine domestication, researchers have identified a lot of valid information regarding the time, the region and the ancestor of the dog. But researchers are still figuring out, why and how this process started. The scavenging hypothesis, first proposed 2001 by Ray and Lorna Coppinger, proclaims the first human waste dumps as the ecological niche for the self-domestication-process of dogs. Many scientists refer to that model, sometimes partly modified. The scavenging hypothesis is broadcasted by most public media as the commonly accepted model of dog's domestication. Thus, we have to deal with that popular model. Based on a broad multi-disciplinary approach like human evolution, archaeology, palaeogenetics, psychology and neurobiology, we will look for evidence. Investigating nine assumptions of the scavenging hypothesis we did not find any evidence. Dog's domestication started thousands of years before the advent of food waste dumps. The scavenging hypothesis cannot explain why only wolves and never foxes nor jackals have been domesticated. Paleolithic people and ancient wolves were living together closely in the same ecological niche hunting the same prey with the same cooperative methods. It is likely that they met very often and knew each other very well. We have some hints, that ancient wolves and people treated each other with respect cooperatively. We have hints for an active cooperation from humans and dogs starting in the Upper Paleolithic period long before it would have even been possible scavenging human waste. We have hints for emotional bonds between ancient people and dogs. Emotional bonds would have been unlikely for an animal hanging around human settlements while scavenging carrion and feces, like the scavenging hypothesizes describe. Looking at recent dogs and humans we have evidence for strong unique similarities in the psychological and neurobiological structures eventually allowing interspecific bonding, communication and working. Interspecific cooperation decreased the level of the stress axis of both species in the Paleolithic period and even does so today, what improves our social and cognitive abilities. We propose that dogs domestication could be understand as an active social process of both sides. Further investigations need a closely networked multidisciplinary approach.
... On the human side, as also discussed in the previous section, our self-domestication resulted in reduced levels reactive aggression, hypersocial behavior, and increased cooperation skills. In turn, these changes seemingly brought about improved social learning, abilities, an enhanced working memory, greater emotional inhibition, better executive functions, and a improved ToM, with these modifications ultimately promoting changes in brain function and anatomy due to the increased interspecific prosocial contacts (see Pörtl and Jung, 2017;Jung and Pörtl, 2018 for details). All these are important changes for achieving enhanced communication abilities. ...
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A decade of research on domestic dogs' responsiveness to human actions has led some to believe that all members of the species Canis familiaris possess a human-like social cognition not shared by their nondomesticated relatives. However, comparative studies on diverse populations of domestic dog are lacking, making species-wide generalizations premature. In this study we present the performance of one under-represented population, stray dogs living in shelters, on a human-guided object-choice task. Unlike pet dogs, shelter dogs universally failed to follow a momentary distal point to a target location in initial tests, although they were able to follow a simpler form of human point on the same task. Furthermore, the majority of subjects learned to follow a momentary distal point to a target when given additional training trials (experiment 2). Dogs' sensitivity to human gestures may not be entirely explained by phylogenetic variables; rather, the interactions between genetic, developmental and experiential variables must be considered.
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Basic tendencies to detect and respond to significant events are present in the simplest single cell organisms and persist throughout all invertebrates and vertebrates. Within vertebrates, the overall brain plan is highly conserved, though differences in size and complexity also exist. The forebrain differs the most between mammals and other vertebrates. The classic notion that the evolution of mammals led to radical changes such that new forebrain structures (limbic system and neocortex) were added has not held up nor has the idea that so-called limbic areas are primarily involved in emotion. Modern efforts have focused on specific emotion systems, like the fear or defense system, rather than on the search for a general purpose emotion systems. Such studies have found that fear circuits are conserved in mammals, including humans. Animal work has been especially successful in determining how the brain detects and responds to danger. Caution should be exercised when attempting to discuss other aspects of emotion, namely subjective feelings, in animals since there are no scientific ways of verifying and measuring such states except in humans.
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Biologists, breeders and trainers, and champion sled dog racers, Raymond and Lorna Coppinger have more than four decades of experience with literally thousands of dogs. Offering a scientifically informed perspective on canines and their relations with humans, the Coppingers take a close look at eight different types of dogs—household, village, livestock guarding, herding, sled-pulling, pointing, retrieving, and hound. They argue that dogs did not evolve directly from wolves, nor were they trained by early humans; instead they domesticated themselves to exploit a new ecological niche: Mesolithic village dumps. Tracing the evolution of today's breeds from these village dogs, the Coppingers show how characteristic shapes and behaviors—from pointing and baying to the sleek shapes of running dogs—arise from both genetic heritage and the environments in which pups are raised. For both dogs and humans to get the most out of each other, we need to understand and adapt to the biological needs and dispositions of our canine companions, just as they have to ours.
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We review the evolution of domestic animals, emphasizing the effect of the earliest steps of domestication on its course. Using the first domesticated species, the dog (Canis familiaris), for illustration, we describe the evolutionary peculiarities during the historical domestication, such as the high level and wide range of diversity. We suggest that the process of earliest domestication via unconscious and later conscious selection of human-defined behavioral traits may accelerate phenotypic variations. The review is based on the results of a long-term experiment designed to reproduce early mammalian domestication in the silver fox (Vulpes vulpes) selected for tameability or amenability to domestication. We describe changes in behavior, morphology and physiology that appeared in the fox during its selection for tameability, which were similar to those observed in the domestic dog. Based on the data of the fox experiment and survey of relevant data, we discuss the developmental, genetic and possible molecular genetic mechanisms underlying these changes. We ascribe the causative role in evolutionary transformation of domestic animals to the selection for behavior and to the neurospecific regulatory genes it affects.