Self-domestication: what it is and how it is expressed in evolution

It is often said that nature is cruel. This popular expression could be true at least from our prism, considering that many of the beings that populate the planet resort to violence with the firm purpose of survival (leaving behind breathtaking scenes from the perspective of the eye human).

Such observations led to the suspicion that aggressiveness was an adaptive trait for many years, and In fact, this could be considered if we only focused on inter and intraspecies conflict as a criterion of judgment.

However, various theories also suggest that evolution may reward animals (including humans) that do not resort to aggression as part their behavioral repertoire, through different mechanisms (such as collaboration in obtaining food) that increase their probability of continuing with lifetime.

In this article we will address precisely this issue, focusing on an essential concept: self-domestication. Examples of its effects in the behavioral, physiological and morphological sphere of living beings will also be detailed.

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What is self-domestication

Self-domestication is a theoretical postulate that proposes that animals, both human and non-human, are subjected to a selection process in which their youthful traits are particularly retained. That is, aggressiveness relative to adulthood would become a counterproductive trait for survival in environments where collaboration is necessary. In this way, the adaptation process would be facilitated in subjects with a greater capacity for establishing social ties (more related to early stages of development).

What is really true is that in nature there are many animals that resort to aggressive behaviors in order to deal with the demands of their environment, since through them they respond to the usual threats with which they coexist in their daily lives. It is an adaptive quality when there are high levels of competitiveness to conquer the necessary resources for survival, but that it lacks this virtue in historical places or moments where violence leads to ostracism within the ecosystem (and subsequently to death). In this sense, domestication would be understood as the deepest form of collaboration of two species, and a fundamental example for evaluate the effect of the possible “friendship” of two animals that inhabit the same space (“domes” is a Latin word that translates as "home").

When observing in detail any domesticated animal they are not only appreciated changes in their behavior; rather, these transcend the morphological, physiological and cognitive dimensions. For example, scientific evidence shows that such specimens show different pigmentations (softer tones) than other members of their species; as well as smaller teeth, substantial flattening in the jaw / muzzle projection, a reduction of the cranial perimeter and a substantial similarity with characteristic features of the previous stages of its physical development. That is, they take on a friendlier or less hostile appearance.

Natural selection leading to domestication can happen both automatically and artificially.. This last case is the best known, the dog / wolf being the most obvious exponent to illustrate it. Today we know that the relationship between man and dog had a difficult beginning (with numerous attacks on each other), but that it began to improve from chance encounters in which wolves (canis lupus) approached human territory to peacefully ask for some food.

This non-aggressive approach led to these animals being able to afford the invaluable help of another different species, establishing between the two a future collaboration that would benefit the survival of both. In this way, new adaptations of wolves would emerge, which would be the most primitive ancestors of what we know as dogs (canis lupus familiaris). Well, this process is based on an interspecies relationship, which has also been reproduced in nature with other animal varieties (spontaneously).

As can be seen, self-domestication necessarily starts from the selection of non-aggressive individuals through integration with other species. belonging to the same ecosystem, decisively overcoming the adaptive qualities attributed to aggressiveness (as a confrontation). In such a way, animals with much less tendency to attack inter / intra species would arise from itas well as a more refined and prosocial coping style.

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What are the differences between domesticated and non-domesticated animals?

The domestication process causes a series of changes in all animals, and this includes humans. Next we will see the three most important, according to the specific dimension to which they could belong: morphology, physiology and behavior.

1. Morphological changes

In general, it can be said that changes in the animal's appearance are associated with a kind of regression towards the physical characteristics of the juvenile stage, which highlights a softening of facial features and corpulence in absolute terms. In many of the species studied (including dogs, primates and pigs) skulls with a smaller perimeter (with respect to the average of the species in the wild) and a flattening of its face, which is known as neoteny (juvenile appearance).

The teeth (which are used as a weapon for aggression) are also reduced in size, and the anatomical discrepancies would be noticeably diluted. between the sexes (dimorphism), as there is usually greater similarity between female and juvenile physical appearance in most species animals.

2. Physiological changes

Animals subjected to a self-domestication process also show a series of changes in metabolic and endocrine functioning. For example, many studies indicate that the hypothalamic pituitary adrenal axis (or HHA) becomes underactive at baseline (which would translate into low levels of stress in a resting situation), but that its function would increase rapidly when a competitive effort was required (mediated by steroids).

Many authors interpret this biphasic response as a tendency to passive coping styles among self-domesticated animals, as well as the avoidance of potentially dangerous situations (unwillingness to act aggressively).

In the specific case of foxes, significantly higher levels of the neurotransmitter have been observed serotonin (5-HT) among those who have undergone a domestication process, this being one of the modulators neurobiological fundamentals of active and / or passive aggressive responses (with predatory or defensive intent against attacks). In addition, neuroimaging functional tests also suggest low levels of limbic reactivity when exposed to threatening situations (more specifically a tonsillar hypoactivation), which indicates a reduced experience of fear (this being one of the emotions that most frequently triggers aggression responses defensive).

Finally, it has also been observed that domesticated animals show an alteration in their reproductive cycles, and above all a significant increase in their frequency and duration. This physiological process would be accompanied by mating efforts characterized by a low incidence of coercive acts (or of imposition by force of the one who enjoys a greater hierarchical dominance), including more sophisticated and relevant (and even more beautiful) mating rituals.

3. Behavioral and cognitive changes

Behavioral changes are, of all those related to the theory of self-domestication, the most numerous and well-known. They have been described in a wide variety of different animals, but especially among canids and primates (because they are animals close to humans at an evolutionary or relational level). In this way, for example, wolves are known to be much more aggressive than dogs (who limit themselves to barking at presence of a rival group), or that bonobos tend to be more peaceful and tolerant than other species of apes (such as the chimpanzee).

It is precisely the latter that have monopolized, at least during the last decade, a greater volume of research. Bonobos and chimpanzees can provide information on the attitudinal / social aspects that emerge from the self-domestication process, since there is a broad scientific consensus that the first of them has experienced it in a much more pronounced way than the second, which merits interesting comparisons of intraspecies interactions in their respective environments natural.

The main conclusions that have been drawn about this are suggestive that (in general) bonobos are animals with a greater “social commitment” with respect to their family and herd, which is manifested in a notable tendency to share food (even in cases in which the recipient of the same has not collaborated in its search or in its storage). They are also known to resort to gambling and other recreational activities (which are not in themselves an adaptive purpose) which has been considered an indirect indicator of intelligence.

Bonobos have also been shown to be more collaborative animals during interactions with other species, including humans, showing more obedience to instructions whose compliance may provide incentives of some kind (food, toys, etc.). They also seem much more capable of inhibiting the urge to achieve a quick but discreet reward, preferring to wait some time to see their reward increased. This fact suggests a greater tolerance for frustration.

The researchers' conclusions suggest that bonobos retain many more of the behaviors of their early youth, including those with a prosocial essence, and that they maintain them throughout life. This fact could be one of the consequences of their self-domestication, and obey the differential evolutionary process that they had to face (with respect to that of chimpanzees). Both the environment and the concomitant circumstances in their respective "stories" have been postulated as explanatory variables for their differences in habits and customs.

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Does it also occur in humans?

Apparently the answer to this question is yes. There are many studies that suggest that changes in our physical appearance with respect to our primitive ancestors (superior cranial sphericity, loss of body hair, decrease in muscle mass, flattening of teeth, retraction of the jaw or general infantilization of the face) are due to this process, and that these they relate to our extraordinary cognitive and social milestones; as well as technological and even creative / artistic.

The modern human face has exceptional neotenic properties in nature (youthful appearance). In fact, the face of the adult male is considered to be very similar to that of a teenage Neanderthal. This process (which also took place in other extinct hominid species, presenting itself in the form of a mosaic) has developed in parallel with the distancing of man of wild nature and its approach to societies in which multiple specimens participated (whose operation required extraordinary skill cognitive).

In summary, the changes that stemmed from life in large communities and from collecting habits They not only outlined our physical appearance, but also the way we interact with others and with the environment around us. The process of self-domestication of the human being, understood as the tendency towards intra-species collaboration, can be fundamental to understand who we are and why.

Bibliographic references:

• Bidau, C. and Martinez, P. (2017). Cats and dogs cross the line: Domestic breeds follow Rensch's rule, their wild relatives do not. Vavilov Journal of Genetics and Breeding, 21, 443-451.
• Jablonka, E., Ginsburg, S. and Dor, D. (2012). The co-evolution of language and emotions. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 367, 2152-2159.