Human self-domestication – the development of an idea
Charles Darwin was the first to systematically examine biological changes in species under artificial breeding conditions. Even though he did not refer to the question of human self-domestication in his two volumes on Variations of Animals and Plants under Domestication , Darwin proposed clear definitional criteria for the process of domestication. He emphasized (1) that the domestication of animals is more than taming, (2) that it represents a goal-oriented process for human purposes, (3) that the variability of physical and ‘mental’ characteristics is greater in domesticated species than in their wild ancestors, including the occurrence of dwarfism and gigantism, (4) that the behavioural plasticity and educability of domesticated species is greater, and (5) that the brain size of domesticated animals is smaller than that of their wild ancestors’.
In spite of these unequivocal definitional criteria, Darwin was remarkably vague regarding the possibility that humans could have undergone domestication. In The Decent of Man , he wrote the following (the most critical phrases are highlighted in italics by the author): “It is, nevertheless, an error to speak of man, even if we look only to the conditions to which he has been exposed, as ‘far more domesticated’ (Blumenbach 1865) than any other animal. … In another and much more important respect, man differs widely from any strictly domesticated animal; for his breeding has never long been controlled, (this is not true! The social hierarchy is a reproductive selection machine!) either by methodical or unconscious selection. No race or body of men has been so completely subjugated by other men, as that certain individuals should be preserved, and thus unconsciously selected, from somehow excelling in utility to their masters. Nor have certain male and female individuals been intentionally picked out and matched, except in the well known case of the Prussian grenadiers;” (p. 29) … By contrast, in another paragraph Darwin stated: “We might, therefore, expect that civilized men, who in one sense are highly domesticated, would be more prolific than wild men. It is also probable that the increased fertility of civilised nations would become, as with our domestic animals, an inherited character …” (p. 45–46). (Darwin was a man of his time and class; likely oblivious to de facto social selection. People married and reproduced within their “proper place” on the pyramid.
With respect to brain size Darwin argued, however, that in contrast to domesticated animals the human brain and skull has increased over time. Nevertheless, in the chapter on human races, Darwin reiterates that “man in many respects may be compared with those animals which have long been domesticated, …” (p. 178); and later: “With man no such question can arise, for he cannot be said to have been domesticated at any particular period” (p. 183). And finally: “With our domestic animals a new race can readily be formed by carefully matching the varying offspring from a single pair, or even from a single individual possessing some new character; but most of our races have been formed, not intentionally from selected pair, but unconsciously by the preservation of many individuals which have varied, however slightly, in some useful or desired manner” (p. 188). In summary, although Darwin did not hold a clear position concerning the possibility that domestication could have taken place in homo sapiens, he pointed to the fact that no scientific proof in favour of such a hypothesis existed, particularly, due to a lack of goal-directedness or conscious selection of traits. However, he also made clear that humans might share some characteristics typical of domesticated animals such as increased fertility.
In the biological literature following Darwin, the term “domestication” became increasingly poorly defined. The criterion of intentional and goal-directed selection, which according to Darwin’s definition was critical for domestication, was largely replaced, at least with respect to humans, by the equation of culture and civilisation with domestication. (One example of intentional goal directedness: The Harem – females selected for social position, connection to allies or subjugated nations, tameness and beauty and continually replenished with youthful baby producers. A broad “blood” base (genetic pool) was available: a veritable farm for producing “top males” for the continuation of a dynasty.
An extensive evaluation of the topic was put forward by Eugen Fischer in his essay on Die Rassenmerkmale des Menschen als Domestikationserscheinungen (“The racial characteristics of man as a result of domestication”, 1914) . A couple of years later, Fischer became known for his publication of Grundriß der menschlichen Erblichkeitslehre und Rassenhygiene (“Outline of human genetics and racial hygiene”), which he edited together with Erwin Baur and Fritz Lenz in 1921 ; all authors later became leading authorities in Nazi eugenics and supported the legalisation of sterilisation and dismantling of welfare institutions to reinstitute the laws of natural selection .
( A prime human conceit that has ravaged the planet: we are so intelligent that our blunders-efforts at reshaping natural processes and entire ecologies are de facto improvements on nature. WE ARE NOT THAT SMART!)
In his essay on the domestication of man, Fischer suggested that domestication should be defined as a condition in which “the nutrition and reproduction has been influenced over a number of generations by humans” (author’s translation). In line with these greatly relaxed definitional criteria of domestication, Fischer reasoned that humankind should be considered domesticated from the beginning of its existence. (We were never wild animals?) Fischer considered racial differences to be the result of domestication, because “almost all characteristics of human races could be found in domesticated animals, except for the low variability of the external ear and the lack of dappling of the skin or hair.” Interestingly, Fischer regarded blond hair, blue eyes, and bright skin colour of Europeans as signs of domestication-induced partial albinism, as well as, dwarfism and gigantism in some populations, racial differences concerning the disposition for obesity, temperament, character and intelligence. Even “the permanent female breast indicates domestication much like the udder of domesticated cattle” (author’s translation) . However, the point that “Aryans” should be carriers of outstanding signs of domestication was apparently overlooked, a point to which I will return in the discussion. Remarkably, however, the very same attitude towards domestication and racial hygiene including support of sterilisation was also found in leading Jewish scientists such as Richard Goldschmidt, who was Professor at the Kaiser Wilhelm Institute for Biology in Berlin-Dahlem . Goldschmidt argued that the abandonment of natural selection and “radical extermination of the unfit” (Goldschmidt, 1933, pp. 214; author’s translation) ought to be replaced by positive and negative eugenic measures (apparently, Goldschmidt later realised that the Nazi regime held an even more radical position regarding eugenics and was expatriated by the Nazis in 1935; he was appointed Professor of Genetics and Cytology at Berkeley, CA). Even anthropologist Franz Boas, who was not a racist and strongly opposed the Nazi regime, described curly hair, variation in stature and increasing or decreasing pigmentation of the skin as signs of human domestication, but was inconclusive about how much environmental and genetic factors contributed to these variations . Thus, although Fischer and colleagues may, to a certain degree, have had an opportunistic interest in mixing scientific ideas with political claims, the association of acknowledging the self-domestication hypothesis with eugenic consequences during the 1930s was not only an issue for racist scientists. (The misconception / mixing of non-scientific social, political, and religious beliefs has not disappeared in psychology. Biological sources are sought for justification of discrimination. These prejudices do not negate the possibility of domestication, but unfortunately, have made it a “shady” subject for study. The same problem taints psychology and its support and contributions to American Eugenics movement.)
In the 1920s, another, entirely independent biological concept was adopted from embryology to explain human self-domestication. The Dutch anatomist Louis Bolk (1926)  postulated that adult humans would resemble juvenile apes, and that the retention of juvenile characteristics of the ancestral species into adulthood of the descendant, referred to as “foetalisation” or “neoteny”, could be associated with the process of domestication. For example, the zoologist Max Hilzheimer (1926/1927) argued that “the recent European should be considered the most progressively domesticated form whereas Neanderthals were much less juvenilised” (author’s translation) due to the more pronounced retention of juvenile traits in anatomically modern humans compared to Neanderthals (at that time, it was not known that Neanderthals were not ancestral to anatomically modern humans) . The parallel drawn between domestication and neoteny is interesting in light of the currently resurrected debate about human self-domestication (see below).
In the 1940s Nobel laureate Konrad Lorenz’ published some speculations on the relation of human psychological capacities to the process of domestication. In his article Durch Domestikation verursachte Störungen arteigenen Verhaltens (“Domestication-induced disorders of species-typical behaviour”, published in 1940) Lorenz reiterated parallels between the living conditions of civilised inhabitants of metropolitan areas with domesticated animals, which he thought indicated signs of degeneration . (The assumption of “degeneration” damaged scientific research.)
Lorenz proposed that the intensity and frequency of instinctual patterns of behaviour were altered under these conditions, leading to a hypertrophy of some instincts due to a lowered releasing threshold and to a functional disruption of species-typical behaviours. Beside the alleged domestication-associated morphological features in human beings, such as shortening of the extremities and of the base of the skull, atony of the muscles, and obesity, which he later subsumed under the term ‘Verhausschweinung’ (a term hard to translate that roughly compares the physical appearance of human beings with domesticated pigs), Lorenz described a domestication-associated diminished social sensitivity and a functional disruption of love, marriage, and the “copulation drive”. Apart from his appallingly coarse language, which conformed to the writing style of that time, Lorenz did not refrain from discussing racial hygienic consequences such as the “extermination of ethically inferior people.” Moreover, and from our perspective today virtually ridiculous, Lorenz proposed a positive selection for Anständigkeit (decency) and for the physical ideal of the ancient Greek. (As modern western “civilized” and Christian people, we applaud ourselves for having high ethical and moral standards, but what is the underlying goal of military, economic, and cultural invasion by any nation? It’s murder, rape and pillage – virtual extinction of peoples and cultures – on a massive industrial scale. “Democratization=Domestication” How many so-called primitive tribal people, religious minorities, and any “outgroup” that is labeled enemy, or any enemy at all is “cleansed” of its heritage, values beliefs and practices by military, social and corporate actions? Civilian casualties, millions of displaced refugees – hypocritically disguised as the inevitable consequence of the mysterious “fog of war.”)
By contrast, in his chapter on Psychologie und Stammesgeschichte (“psychology and epistemology”, first published in 1943)  Lorenz took over Arnold Gehlen’s idea that human beings were specialised in being non-specialised. Gehlen had acknowledged Bolk’s and Hilzheimer’s hypotheses as scientific proofs for his thesis of man as “Mängelwesen” (“deficient being”). Following Gehlen, Lorenz highlighted man’s lack of physiological specialisation while rejecting the hypothesis of deficiency. In contrast to his earlier exclusively negative approval, Lorenz now accepted the hypothesis of domestication-associated neoteny, which accounted for the positively asserted human “Weltoffenheit” (“cosmopolitanism”) and persisting explorative behaviour. This was new, since he now ascribed to neoteny a variety of human behavioural and psychological features in addition to his physical characteristics. Even in his later writings, however, Lorenz stuck to his culturally pessimistic attitude, while partially backing off from his writings during the Nazi regime.
Since the 1960s, both the foetalisation and the domestication hypotheses concerning humans have been refuted by various scientists. Starck (1962), for example, criticised that Bolk’s hypothesis had been so broadly accepted simply because the many problems of explaining human evolution could be resolved with apparent ease. According to Starck, hairlessness and the reduction of pigmentation of the skin (a geographic phenomen due to varying solar radiation) were more reliably explained by chance mutations rather than by foetalisation. Moreover, the retention of juvenile characters (i.e. neoteny) did not sufficiently explain the increased variation of traits under domestication . In addition, Herre and Roehrs (1971) rejected the human self-domestication hypothesis for its lack of goal-directedness and artificial selection of traits; nor was there evidence for a “wild” ancestral human species from which a domesticated homo sapiens should have derived. They further argued that a reduction of instinctual patterns of behaviour in human beings could also better be explained by a more sophisticated cortical control rather than domestication . (Objections based on the lack of scientific evidence at the time and the resistance to Homo sapiens the animal.)
As with many scientific ideas, these hypothesis of human self-domestication has recently been revived as a possible explanation of changes of human physical traits since the late Pleistocene changes include the reduction of body size and decrease in skeletal robusticity, modifications in cranial and dental features including reduction in cranial capacity, shortening of the facial region of the skull and maleruption of teeth, and reduction in sexual dimorphism. In contrast to earlier biological writings, other domestication-associated features observed in animals such as an increased variation in skin colour, increasing fat storage, earlier sexual maturation and activity, and reduction in motor activity are not discussed with respect to human self-domestication in recent accounts . It is indeed plausible to assume that these changes could have taken place due to the creation of an artificially protective environment after humans adopted a more sedentary lifestyle in the Neolithic period, thereby relaxing natural selection pressures. (But! selection pressures changed and increased due to selection by a new urban and dietary environment that required behavioral and reproductive adaptation. Reproduction became controlled by social customs, class barriers to reproduction partners, and selection of females for tameness.)
Similarly, the idea that foetalisation and domestication could be related has recently been highlighted in a seminal paper comparing anatomical features and behaviour of apes and humans . The authors argue that changes in social structures of early humans, compared to our closest living relatives, the chimpanzee, could have favoured the selection against aggression, and that such selection was accompanied by a reduction of sexual dimorphism in humans and the retention of juvenile characteristics in body shape and behaviour. Interestingly, a parallel development has been proposed in the bonobo, which displays more neotenic physical features and is much less aggressive compared to the common chimpanzee .
From a biological perspective the greatest dispute with regard to physical changes in anatomically modern humans akin to domestication pertains to a slight but measurable decline of brain volume from around 1,400 cm3 to roughly 1,300 cm3, which could be interpreted in further support of the human self-domestication hypothesis. However, this decline in stature was accompanied by a reduction in body size such that the allometric brain-body relation remains unchanged . In contrast to humans, domesticated animals show a large disproportionate decline of brain size by up to 30%, especially of the sensory perceptual centres, compared to their wild ancestral species, yet no such pronounced decline has convincingly been demonstrated in any human population.
We have a huge stumbling block in the investigation of self-domestication in humans: Which “human” is our wild ancestor?
Part 3 next…