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Bruno Titelfoto Schwarzbuch Hund
 

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Publications
Bücher von Christoph Jung und Daniela Pörtl
*Dog behavior Vol 3, No 2, 2017

Is dog domestication due to epigenetic modulation in brain?

Daniela Pörtl, Christoph Jung


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.

Keywords
dog, wolf, domestication; stress-axis; epigenetics; coevolution

DOI: https://doi.org/10.4454/db.v3i2.55

 

**Cultural Evolution Society Jena, September 2017:

Dog domestication and human cultural evolution – co-evolution of cognitive abilities favoured by epigenetic modulations in limbic brain regions


Dogs are the first domesticated animals living together with humans at least 25.000 years - assisting humans until today with hunting, protecting, herding. But primarily dogs have always been important social bonding partners to humans. Recent scientific research proves mutual empathy between humans and dogs. Domestication evoked tameness, that means decreased flightdistance chiefly concerning to humans. And in fact, in the Siberian farm-fox experiment, demonstrating a domestication process, first changes have been found in a decreased activity of HPA stress axis promoting domestication syndrome. Now I will go on to present the hypothesis of the

Active Social Domestication (ASD)

– an epigenetic based model of a self-domestication process due to interspecific emotional attachment During the Palaeolithic period humans and wolves lived as cooperative hunters in similar family clans in the same ecological niche.

Similar social skills and the evolutionary continuity of mammalian brains allowed both of them initial interspecific (pro)social communication achieving an evolutionary benefit for both. Knowing each other reduced stress and helped becoming confident. Behavioural cultures between wolf clans and human clans were formed, individual bonding, genetic isolation and domestication processes began. Epigenetic modulation of stress axis caused by social behaviour Scientific studies prove, that prosocial care enhances via epigenetic modulations glucocorticoid negative feedback loop in brain, thus decreasing the activity of stress axis and therefore increasing the activity of cross-regulated calming system. This suggests a direct relationship between variations in prosocial behaviour and development of HPA responses to stress.

In the Palaeolithic period described epigenetic modulations induced lower cortisol levels in all individuals within the attached wolf-human clan, prosocial behaviour improved enhancing mutual empathy and interspecific in-group behaviour. Eventually the wild wolf became a tame wolf regarding known individual humans as his pack mates.

But a tame wolf is not yet a dog.

Permanent high cortisol levels impair learning and executive functions. But epigenetically decreased cortisol levels improve social learning capabilities and enabled tame wolves to develop increased emotional and cognitive empathy concerning to humans. Thus first dogs have learned to use human communicative cues and eventually dogs integrated themselves into human social structures, accepting humans as their preferred social binding partner. But what about ancient humans?

Did dogs domesticate humans as well?

During the dog domestication process all individuals of the attached human-wolf clan experienced the same epigenetic modulation of stress axis due to increased interspecific prosocial contacts. Hence it is reasonable to proclaim that the dog domestication had probably influenced human social and cognitive development as well. And in fact, within a narrow time frame of dog domestication, archaeologists describe a sudden further stage of human cultural development in the Aurignacien; first flutes, sculptures, cave paintings and javelin spins occurred. Thus it is reasonable to assume that dogs have influenced human cultural development not only with assisting humans, but also we provide that dogs improved human cognitive capabilities additionally in the sense of a human self domestication process, thus we can think about co-evolution. And even today social interaction between humans and dogs still reduce stress in both of them and invigorate therefore social and learning abilities, which is known to be the reason of dog facilitated therapy in medical treatment.

Daniela Pörtl



*** Poertl D. Epigenetic regulation of the hypothalamic-pituitary-adrenal stress axis and its effects on social behaviour Exp Clin Endocrinol Diabetes 2013; 121 - OP5_29 DOI: 10.1055/s-0033-1336637

Abstract

Activity of the hypothalamic-pituitary-adrenal (HPA) stress axis is influenced thru enhancement of the corpus amygdala and inhibition thru the hippocampus.

Glucocorticoid receptor (GCR) density in the hippocampus is likely to affect its inhibitory effect on this system. Epigenetic input is known to impact regulation of GCR expression. Factors described include down-regulation of GCR expression by enhanced methylation of GRexon1;7promotorbloc as a consequence of increased methionine ingestion. Psychosocial factors like licking and grooming enhance GCR expression via increased serotonin and subsequently increased NGF levels binding on GRexon1;7promotorbloc.GCR density and thereby activity of the stress axis and with its characteristics of the individual are determined in the childhood but stay variable during adolescence and adulthood.

This model has been evaluated to establish a new theory of active social domestication from the wolf to the dog, considering that the change of the HPA-axis via epigenetic induced GCR expression is the main aspect for decrease the flightdistance of a wild wolf to domesticated dog.

In this way active social interaction between human and wolf resp. dog grows, influenced due to the evolutionary continuity of same neural structures. So even human social learning ability could be improved. It may, however, also provide a new insight in the biochemical mechanisms of known phenomenons like infantile imprinting and psychotherapy exspecially concerning post-traumtic syndrome.