Self-domestication
[3][4] In general, domesticated animals possess common characteristics that differentiate them from their non-domesticated counterparts (for example, in the case of Canis familiaris compared to their relatives, Canis lupus, among many other cases): they tend to be more docile and playful, exhibit less aggressive behavior, and show marked neoteny, often resulting in a smaller body, a slightly smaller brain and skull, as well as shorter teeth and snout.
[5] However, the studies of Dimitri Beliayev in the 20th century were important for the proposal: research on the silver fox demonstrated that in the process of animal domestication, simultaneous changes occurred in behavior (lower levels of adrenaline were observed) and in coat color (alterations in pigmentation): adrenaline could share a biochemical pathway with melanin, a pathway that would be altered during the process of artificial selection.
[7] In 2014, scientists Adam Wilkins (from Humboldt University, Berlin), Richard Wrangham (from Harvard University, Massachusetts), and Tecumseh Fitch (from the University of Vienna) proposed that the common origin of these changes lay in neural crest cells, exclusive stem cells of vertebrates that migrate to different parts of the body during the embryonic phase, giving rise to the adrenal glands (responsible for managing the fear and stress response through adrenaline production), melanocytes (responsible for producing skin or coat melanin), and jaws simultaneously.
In July 2019, a team from the Institute of Marine Sciences of Barcelona described, through the methylation of certain genes in DNA, the epigenetic and genetic changes through which neural crest cells were reduced.
[1] Cedric Boeckx, one of the researchers in this study, states:"We believe this means that the genetic network of BAZ1B is an important reason why our face is different compared to other already extinct ancestors, like the Neanderthals [...].
"[11] Further research has confirmed that Ardipithecus possessed paedomorphic cranial base angulation, position of the foramen magnum as well as vocal tract dimensions.
If this thesis is correct then not only human social behavior but also language ability originally evolved through paedomorphic skull morphogenesis via the process of self-domestication.
Occurring between 40,000 and 25,000 years ago, this rapid neotenization has been explained as the result of cultural selection of mating partners[13] on the basis of variables lacking evolutionary benefits, such as perceived attractiveness, facial symmetry, youth, specific body ratios, skin tone or hair, none of which play any role in any other animal species.
It led to rapid changes typical for domestication, such as in cranial morphology, skeletal architecture, reduction in brain volume, to playful and exploratory behavior, and the establishment of thousands of deleterious conditions, syndromes, disorders and illnesses presumed absent in robust humans.
Using the fossil record to compare Homo sapiens to pre-sapiens ancestors, archaeologists observed many of the same telling phenotypic characteristics that emerge as a consequence of self-domestication in animals.
Academics have raised concerns with inconsistencies with the self-domestication hypothesis, pointing out that it isn't logical that humans could potentially be domesticated given the profundity of violent acts for which they are responsible.
During periods of high population density, higher tolerance of associates may be favored due to an increased reliance upon social networks for reliable access to otherwise limited, scarce resources like food.
