Part 3 Human self-domestication / Martin Brüne


Impact of the human self-domestication hypothesis on psychiatry

Quantifying the actual impact of the self-domestication hypothesis on psychiatry is a difficult endeavour. As psychiatry began to one-sidedly “biologise” mental disorders, including concepts of aetiology and treatment by the turn of the 20th century [9], human self-domestication was readily acknowledged as the primary cause of degeneration, which allegedly had already begun to deteriorate the genepool of populations or “races”. The impact of the self-domestication hypothesis can perhaps be estimated according to the influence of prominent psychiatrists on national and international developments in psychiatry, who proclaimed the validity of the degeneration paradigm, and hence, self-domestication.

In the first three decades of the 20th century, German psychiatry had certainly a leading role worldwide in terms of scientific competence and recognition. For example, many psychiatrists from abroad were fellows at the newly founded German Kaiser Wilhelm Institute for Psychiatry headed by Emil Kraepelin. Kraepelin and his pupil and successor Ernst Rüdin, who first headed the Genealogical Department of the Research Institute under Kraepelin’s directorship, were two prominent figures who were ardent advocates of the degeneration and domestication hypotheses, and both did not make a secret of their views that domestication was the main causal factor for the alleged increasing prevalence rates of mental disorders and deterioration of the genepool. In his article Zur Entartungsfrage (“On the question of degeneration”, 1908) Kraepelin complained about a steady increase in psychiatric disorders in civilised people, while mental disorders remained comparably rare in “primitive” races [7]. Kraepelin had visited the psychiatric hospital “Buitenzorg” in Java in 1904 and recognised that the “paralysis of the insane” and alcoholism were rare despite a high prevalence of syphilitic infections among the Java people. This, he reasoned, would indicate a greater resistance against diseases in these peoples compared to inheritable germ lesions acquired by the forces of civilisation, which ultimately would lead to an increase of degeneration insanity (“Entartungsirresein”). (Note that Kraepelin adhered to the concept of so-called “blastophtoria” (germ lesion), which reflects Lamarckian inheritance). Kraepelin now subsumed a variety of “symptoms” under the domestication paradigm, such as “weakening of viability and resistance, decreasing fertility (as opposed to Darwin’s observations in domesticated animals), proletarianisation, and moral damage due to ‘penning up people’ (orig. German phrase “Zusammenpferchung”)”. The result would be “effeminacy, stunted growth, and debility” (author’s translation). Kraepelin saw further threats in one-sided “breeding of psychological capacities” in civilised populations, while neglecting physical vigour and the development of the “free will”, all of which for him was most evident in Jewish people. Kraepelin’s language also reflected the tendency toward brutalisation and radicalisation found among many of his contemporaries. Examples are presented here in some detail (and to my knowledge for the first time translated into English) to illustrate the other side of Emil Kraepelin, who is still a highly regarded icon in psychiatry.

Kraepelin was concerned, for example, that “the number of idiots, epileptics, psychopaths, criminals, prostitutes, and tramps who descend from alcoholic and syphilitic parents, and who transfer their inferiority to their offspring, is incalculable. Of course, the damage will be balanced in part by their lower viability; however, our highly developed social welfare has the sad side-effect that it operates against the natural self-cleansing of our people. (He must have been a Republican LOL) We may barely hope that the degeneration-potential will be strong enough in the long term to eliminate the overflowing sources of germ lesion. … Nevertheless, the well-known example of the Jews, with their strong disposition towards nervous and mental disorders, teaches us that their extraordinarily advanced domestication may eventually imprint clear marks on the race” (author’s translation; note that Kraepelin’s ideas on domestication were included in the 8th edition of his “Textbook of Psychiatry”, published in 1909) [23].

Kraepelin’s pupil and successor as head of the Kaiser Wilhelm Institute for Psychiatric Research, Ernst Rüdin, who later was involved, together with Fischer, Baur, Lenz, and others, in the introduction of the “law of prevention of hereditary diseased offspring” (“Gesetz zur Verhinderung erbkranken Nachwuchses”) greatly acknowledged Kraepelin’s attitude. In a paper published in 1910 in the Archiv für Rassen- und Gesellschaftsbiologie (Archives of Racial and Societal Biology), which was one of the leading journals in the field of genetics and eugenics, and of which Rüdin was co-editor-in-chief, he reasoned that the medical care for the insane was a distortion of the natural laws of the survival of the fittest and that medicine would be obliged to clean the genetic pool of the Volk in order to prevent ongoing degeneration [24]. He deplored “alcoholics are forced to go through a cure in order to extend their lives. Self-murderers are prevented by force from killing themselves. Only the mildly psychotic or psychopathic forms may die undisturbed … those who refrain from food intake are artificially nourished and thus brought over death, conditions of weakness, and consuming diseases …

Numerous criminals, who in former times were laid by the heels or hanged on the spot in the name of justice or by the self-help of the Volk (best be translated as “people”, however, with a marked nationalist connotation), are now, if mentally ill, upgraded into the rank of affectionately treated sufferers, or, if criminals, simply imprisoned by virtue of law. Many so-called ‘fools’ formerly perished contemptibly. How many had been burned as witches? Epileptics suffocated or were forever rendered harmless if dangerous to the community.” On the other hand, Rüdin feared that peoples of high value were “destroyed” as “cannon fodder in a peaceful cultural war”, which led him to advocate racial hygiene in order to stop ongoing degeneration [24]. (At first reading, this may merely be received as disgusting racism that has thankfully gone away; however many of these ideas drive psychology, genetic engineering, alteration of the human brain via chemical suppression of symptoms, and in the United States, by the abuse of the mentally ill who are dumped in jails and prisons, and the scandalous state of homelessness and suicide in military veterans.  

Kraepelin’s and Rüdin’s emphasis of degeneration and domestication as a major explanatory factor for psychiatric disorders is intimately tied to Kraepelin’s nosological system, which was, to a great deal, built on the degeneration paradigm.

Although several aspects of eugenic measures – i.e. sterilisation and euthanasia, which drew heavily on the idea that the general population was threatened by increasing domestication – were shared by other leading psychiatrists, the same psychiatrists refuted Kraepelin’s one-sided biological perspective on the aetiology of psychiatric disorders (e.g., [25]), and others explicitly refuted the degeneration paradigm for its scientific flaws [26]; (overview in [9]). Thus, the acknowledgement of the degeneration paradigm and its presumed underlying cause (i.e. domestication), and the support of eugenic measures were, to some extent, separate issues. Hoche, for example, together with Karl Binding, who was Professor of Law, authored one of the most appalling pamphlets entitled “Die Freigabe der Vernichtung lebensunwerten Lebens, ihr Maß und ihre Form” (best be translated as “The approval of the extermination of valueless lives, its measures and procedures”) in 1922, where they outlined euthanasia of mentally handicapped individuals [27]. (The great American contribution to these ideas has been financial exploitation: keep “defective people” alive and overmedicated: Big Pharma profits have skyrocketed to obscene levels as “chemical control ” has overtaken humanitarian values. Why not? Humans are indistinguishable from Lab Rats. Medical doctors have directly created (and profited from) an epidemic of opioid abuse, followed by heroine addiction that is disabling and destroying not only individuals but entire communities; the private prison industry profits from the abuse of throw-away segments of humanity.

In any event, in light of their outstanding position and international recognition it can be argued that the impact of Kraepelin’s and Rüdin’s opinion can hardly be overestimated. Rüdin was highly praised as an internationally leading authority in psychiatric genetics, and invited to attend the International Genetic Congress even in summer 1939. Notably, Rüdin’s work on psychiatric genetics was still cited in a textbook of medical genetics in the early 1970 (quoted from [28]).

After World War II, the self-domestication hypothesis – at least explicitly – has only patchily been mentioned in the psychiatric literature. For example, Ernst Kretschmer (1929) who had pointed to a link between domestication and breeding of intelligence in his essay on the relation of genius and psychopathology [29] abandoned these ideas in later editions [30]. More recently, Richter (1959) assumed an association between civilisation and domestication, which, among other diseases, led to an enhanced vulnerability for mental disorders [31].

Much more popular have been attempts to link psychiatric disorders with the neoteny hypothesis, however, without explicitly referring to domestication. Bemporad (1991), for instance, assumed that a lack of curiosity in “dementia praecox” (schizophrenia) might be related to a dysfunction of regulatory genes controlling neotenic traits [32].

Crow (1995) proposed a failure of neoteny corresponding to a lack of cerebral asymmetry in psychotic disorders [33]. Feierman (1994) speculated on the possible role of neoteny in the aetiology of schizophrenia, rendering “nocturnalism” a neotenic trait [34]. Likewise, Jonas and Jonas (1974) related neurotic patterns of behaviour to neoteny, assuming that the retention of archaic responses could reflect preservation of neotenic features [35]. These ideas have, however, been refuted for their vagueness and implausibility [36]. Moreover, the neoteny hypotheses were entirely disentangled from the concept of degeneration, and, beyond doubt, none of the authors has drawn the slightest moral conclusions from their scientific considerations or confused “is” with “ought”.


The hypothesis that humans could have undergone anatomical and behavioural changes akin to domestication of animals by relaxing the forces of natural selection represents an interesting scientific hypothesis. Even though there is more evidence against than in favour of human self-domestication, at least with respect to brain size, early scientists from Darwin’s times on were fascinated with questions of potential biological consequences of modern civilisation, i.e. partial abandonment of natural selection, for physical and mental well-being (here, it may be worth mentioning that the role of sexual selection has drawn much less attention with regards to effects of modern living-conditions; my personal view is that sexual selection is at least equally important as natural selection for shaping the phenotype of homo sapiens, and that sexual selection simply cannot be eliminated by “civilisation”).

It is obvious that Eugenic distortions are social selection; aggregation of “defectives”  can be removed from the reproductive process through extermination, sterilization, isolation in prisons and lack of medical care for poor women and children and by “internal violence” – Areas of cities in which male gang members conveniently kill each other, and frequently bystanders, who often are children.) 

The hypothesis of human self-domestication may, however, not only illustrate how the acceptance of scientific concepts wax and wane over time, particularly if definitional criteria change, as has been the case with domestication; the main issue here is that scientific hypotheses, particularly if pertaining to human biology, are potentially at risk of misuse. The self-domestication hypothesis came up at a time when cultural pessimism and eugenic optimism prevailed even among scientists [10], and hence, was approved without further enquiry as a valid explanation for an even more scientifically vague concept, degeneration. It was probably only a short step to move on from insufficiently explored scientific ideas to moral claims, a concept shift commonly referred to as “natural fallacy”, first emphasised by David Hume as early as 1739 [37]. In the case of self-domestication, the unfortunate connection between biological science and deduced moral claims was fuelled by a lack of agreement over the question how to deal with naturalistic fallacies, or unwillingness to consider the existence of a naturalistic fallacy for reasons that may have been associated with political opportunism or perhaps firm conviction of some leading scientists in the need for eugenic measures. The atrocities that followed during the Nazi regime in Germany are quite well known and summarised elsewhere (e.g., [38, 39], and shall not be repeated here in detail, but several of the inconsistencies of eugenics may be worth a closer look.

Advocating negative eugenics in order to exterminate or “weed-out” domestication-induced characteristics had a long tradition in Europe and North America long before the Nazis seized power (regarding the eugenics movement in the United States of America, see for example [40, 41]). On the other hand, much less is known about positive eugenics, i.e., breeding programmes to improve the genetic quality of humans, in which undoubtedly racial selection criteria were applied. By the turn of the penultimate century, Willibald Hentschel, for instance, proposed the foundation of “Mittgart” in Germany, a rural community in which 1000 women and 100 men should mate in order to renew the “Germanic race” on a polygamous basis [42, 43] (a very recommendable critique can be found in Oscar Hertwig’s essay Zur Abwehr des ethischen, des sozialen, des politischen Darwinismus, 1918) [44]. Moreover, at the beginning of the 20th century, scientists even inseminated female chimpanzees with the sperm of black men in order to breed cheap working slaves. These experiments failed, however, since the inseminated chimpanzees died during their transport from Africa to Europe [45].

During the Nazi regime, human breeding programmes were put into practice under the leadership of Reichsführer-SS Heinrich Himmler. On his behalf, the “Lebensborn e. V.” was founded to breed Aryans according to anthropological and biometrical criteria such as blondness, blue eyes, form of the skull, etc., but also according to “mental qualities” [46, 47, 48]. All the more grotesquely, Eugen Fischer (1914) considered blondness and blue eyes to be domestication-induced variants, and proposed these for extermination [12].

These inconsistencies notwithstanding, is there anything to learn from the example of how the hypothesis of human self-domestication was conceived in the past for current problems in relation to human biology and society? If the misuse of a controversial concept like self-domestication as scientific underpinning for eugenic measures can be, in part, attributed to a naturalistic fallacy, may this happen again with regards to modern genetics? What are the limits of gene therapy, specifically from a psychiatric point of view? (It’s not “may” this misuse repeat; it has never gone away. We can see eugenic ideas alive and well in theories about ASD and Asperger’s , in which individuals are segregated into “defective brain categories” sanitized by the DSM as “disorders” and the dehumanizing concepts promoted by the Helping, Caring, Fixing Industry, which deny “normality” to neurodiverse thoughts and behaviors. The qualifications for being a “real human” have been narrowed to exclude an obscene and arrogant dictate: only those individuals whom psychologists approve are socially acceptable.

Modern evolutionary biology suggests that physical and mental characteristics of humans represent biological adaptations, albeit there may be plenty of trade-offs and design compromises. We know today that the so-called “diseases of civilization” are not the result of degeneration or domestication; rather, many disorders that supposedly fell into this category result from a mismatch between adaptation and the modern environment; in other words, culture and civilisation shape the actual phenotype. For example, obesity, some subtypes of diabetes mellitus, hypertension, and coronary heart disease probably emerge from the selection of so called “thrifty genes”, which were selected because they were once helpful in the environment of evolutionary adaptedness to maintain the storage of energy during times of relative food scarcity [49, 50, 51, 52, 53, 54, 55]. Only in modern living conditions with our excessive calorie-intake have these adaptations lost their beneficial effect, at least in Western industrial societies. Thus, many modern diseases are more environmentally rather than genetically caused. Moreover, the human genome comprises much less active genes than originally assumed. Pleiotropy, a case in which a single gene influences multiple traits, and the interaction of many genes may therefore be the rule rather than the exception. Thus, it is likely that gene manipulation would have an incalculable impact on traits other than the targeted one; such problems have recently been described in animal experiments, where a gene passed into a genome of mice unexpectedly induced leukaemia [56].

In light of these considerations, can we, at all select mental traits for genetic manipulation? Negative eugenics would imply that distinct predisposing alleles ought to be eliminated from the gene pool of a population: the genes in question would perhaps be detectable in pre-implantation diagnostic screening. Which diseases should be targeted? Perhaps “Alzheimer’s disease” (in this case, had the technology been available, the great philosopher Immanuel Kant would not have been born) [57]; or “depression” (we surely would have prevented the birth of Johann Wolfgang von Goethe) [58]; or last but not least “panic disorder” (in this instance, even Charles Darwin would perhaps have had fallen prey to negative eugenics) [59]. On the other hand, the potential targets of positive eugenics are equally questionable: Would, for instance, “intelligence” be a valuable trait (in most instances, the term is understood as technical intelligence)? We may speculate, however, whether we would have to deal with an increase of autistic spectrum disorders, since these disorders seem to be more prevalent in families in which the fathers and grandfathers had been technicians [60]. (How many myths purported to be scientifically valid, but which are based on coincidental occurrences, must we endure? How many millions of examples can be cited in which famously talented people produce ordinary offspring?)

It is not my intention to demonise gene technology per se, but it should in the first place be made available to benefit those thousands of children and adults in the third world who die from malaria, tuberculosis and other infectious diseases, which further suggests that gene technology companies should promote the production of vaccines and antibiotics. Furthermore, such theoretical models of human genetic improvement disregard the impact of environmental factors in shaping the actual phenotype (note, for example, that many children found in the Nazis’ breeding grounds of the “Lebensborn” after the end of World War II were developmentally retarded, probably due to deficient attachment in early childhood) [46].


Man, like all other living beings, is characterised by specific and unique evolved design compromises, such that most physical and psychological features have costs and benefits [61]. Processes akin to the domestication of animals may, to some degree, have been involved in shaping human nature, but this assumption depends, above all, on the definitional criteria of the term “domestication”. We ought to accept our biological heritage and not be enticed into mistaking biological and technological feasibility for scientific progress. Except for the fact that a manipulation of the human genome would “benefit” only a very small minority of the world population, it is in my opinion more advisable to protect and to recreate environments worth living in, ones which take into account our biological predispositions, a claim made very early by Alfred Russel Wallace, who was a grim opponent of eugenics [62]. Evolution does not know a higher, or a better, not even in terms of humankind.

In this article, the process of domestication has served as an example of how science can be intertwined with philosophical or socio-political issues, known as naturalistic fallacy. In light of the negative connotation of the term “domestication”, “domestication-like” might be a better term for human characteristics that resemble domestication-induced traits in animals. Alternatively, the term might be replaced by the neutral expression of “adaptive changes to sedentism”. This may, at first sight, be only a matter of wording and definition, but scientists should be sensitive that scientific concepts can be associated with values. Similarly, philosophers should not seek for an “is” to support their claims for “ought”, a problem that may be referred to as “reversed naturalistic fallacy”. Beyond all discussion of the validity of the self-domestication hypothesis, the example may support the necessity for an interdisciplinary exchange of ideas between the life-sciences and philosophy to facilitate an open dialogue.

Authors’ Affiliations

Department of Psychiatry, University of Bochum, LWL Hospital


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