Self-domestication

Last updated March 12, 2024

Self-domestication is a scientific hypothesis that suggests that, similar to domesticated animals, there has been a process of artificial selection among members of the human species conducted by humans themselves.^[2] In this way, during the process of hominization, a preference for individuals with collaborative and social behaviors would have been shown to optimize the benefit of the entire group: docility, language, and emotional intelligence would have been enhanced during this process of artificial selection. The hypothesis is raised that this is what differentiated Homo sapiens from Homo neanderthalensis and Homo erectus.^[3]^[4]

Origin and status of the hypothesis

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]

One of the first to scientifically observe that humans present similar traits was the naturalist, anthropologist, and physician Johann Friedrich Blumenbach around 1800.^[6] The author of the thesis "De generis humani varietate nativa" ('On the natural variations in the human lineage') consequently proposed the hypothesis that humans could have been domesticated.

A few years later, Charles Darwin addressed the topic using the theory of evolution, which already considered the process of artificial selection in animals. Unable to explain the concept of human domestication from an exclusively scientific perspective (the question of who domesticated humans could only be answered in religious or theistic terms), he eventually dismissed the hypothesis.^[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. The deficit of these cells would explain the common characteristics of all domesticated animals: tameness, cranial and mandibular reduction, and alterations in pigmentation.^[8]

Of the three members of the research team, it was primatologist Richard Wrangham who translated these results to humans, asserting that humans have "domesticated" themselves through a process of self-selection (a proposal he would elaborate in "The Goodness Paradox: The Strange Relationship Between Virtue and Violence in Human Evolution").

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.^[9] Subsequently, another research team from the University of Barcelona discovered that the BAZ1B gene controls the behavior of neural crest cells. Comparing with the Neanderthal genome, BAZ1B is also related to genes that have many mutations not present in the homologous genes of our past hominini.^[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 [...]. In broad terms, it gives us, for the first time, experimental validation of the autodomestication hypothesis based on the neural crest."^[10]

Hominids

Clark & Henneberg argue that during the earliest stages of human evolution a more paedomorphic skull arose through self-domestication.^[11]^[12] This assertion is based upon a comparison of the skull of Ardipithecus and chimpanzees of various ages. It was found that Ardipithecus clustered with the infant and juvenile species. The consequent lack of a pubertal growth spurt in males of the species and the consequent growth of aggressive canine armoury was taken as evidence that Ardipithecus evolved its paedomorphic skull through self domestication. As the authors state, comparing the species with bonobos:

"Of course A. ramidus differs significantly from bonobos, bonobos having retained a functional canine honing complex. However, the fact that A. ramidus shares with bonobos reduced sexual dimorphism, and a more paedomorphic form relative to chimpanzees, suggests that the developmental and social adaptations evident in bonobos may be of assistance in future reconstructions of early hominin social and sexual psychology. In fact the trend towards increased maternal care, female mate selection and self-domestication may have been stronger and more refined in A. ramidus than what we see in bonobos."^[11]

Further research has confirmed that Ardipithecus possessed paedomorphic cranial base angulation, position of the foramen magnum as well as vocal tract dimensions. This was interpreted as not only evidence of a change in social behavior but also a potentially early emergence of hominid vocal capability. 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.^[12]

The most comprehensive case for human self-domestication has been proposed for the changes that account for the much later transition from robust humans such as Neanderthals or Denisovans to anatomically modern humans. 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. This unintentional auto-domestication, coinciding with the introduction of imagery of female sexuality, occurred simultaneously in four continents then occupied by hominins. 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.^[14]

Of course, these specific views are very clearly based on multi-regionalist perspectives of human evolution which claim modern human populations evolved from relevant archaics present in each world region, as demonstrated in robust skeletal fossils. Such views are largely disproven by genetic evidence supporting the Out of Africa hypothesis with minor inter-breeding and genetic introgression. Despite this, however, human self-domestication entirely within Africa, say, during transition from earlier hominins, especially H. heidelbergensis to H. sapiens remains an open possibility.^[15] This would mean archaics in each region (e.g., neanderthals, denisovans) were largely replaced by self-domesticated H. sapiens as they spread around the globe. This possibility suggests self-domestication played a role in the success of H. sapiens, and the extinction of other lineages.

The idea of self-domestication was used by early Social Darwinism which, according to psychiatrist Martin Brüne in an article "On human self-domestication",^[16] developed from the idea that humans could "perfect" themselves biologically. The idea of self-domestication is also related to the concept of sociodicy.

Modern humans

Physical anatomy

Based on the dating of the fossil record, archaeologists have concluded that self-domestication likely occurred during the Pleistocene, over 300,000 years ago. 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. These features include diminished sexual dimorphism, smaller tooth size, reduction of the cranium, and smaller body size. H. sapiens fossils also demonstrated the flattening of brow-ridge projection and shortening of faces.^[17]

	Reduced aggression	Reduced cranium and skull	White patches	Floppy ears	Flattened facial projection	Small teeth	Juvenility	Curly Tails
Cats	Y	Y	Y	N	Y		N	N
Dogs	Y	Y	Y	Y	Y	Y	Y	Y
Bonobos	Y	Y	Y	N	Y	Y	Y	NA
Marmosets	Y	NA	Y	N	NA	NA	NA	NA
Humans	Y	Y	N	N	Y	Y	Y	NA

Reactive aggression

Richard Wrangham further built upon this body of research, addressing how bonobos and chimpanzees could elucidate development of aggression in humans. 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. Reconciling this paradox, Wrangham posited that self-domestication is the outcome of two different kinds of aggression: proactive and reactive aggression.^[18]

Proactive aggression, which is commonly observed in chimpanzees, is defined as an attack that was planned, motivated by achieving an end goal. Generally, humans demonstrate lower aggression within groups. Reactive aggression, much more closely associated with anger, is characterized as an immediate response to a threat—the human equivalent being "bar fights". Aligned with the behavior of self-domesticated bonobos, humans do not have a high propensity for reactive aggression. This lends further evidence to supporting the self-domestication hypothesis, of which reduced reactive aggression is a central trait.^[18]^[19]

Population density hypothesis

The population density hypothesis attempts to explain the decreased reactive aggression that is observed in modern humans. 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. H. sapiens began to exhibit this higher degree of social tolerance approximately 300,000 years ago, which—if this hypothesis upholds—would be associated with a higher population size. However, recent genetic data has currently put this hypothesis to rest, as H. sapiens actually underwent a population decline about 200,000 years ago.^[17]

Language-based conspiracy

The language-based conspiracy provides a convincing argument—and is currently the best-supported theory—explaining why reactive aggression was selected against in modern humans, thereby resulting in self-domestication. H. sapiens are theorized to have developed an elegant propensity for language that surpassed its predecessors, including H. neanderthalensis. Enhanced linguistic ability would have allowed for greater suppression and control over a power-hungry member of early hunter-gatherer societies. Those who attempted to achieve dominance over others would be subject to capital punishment, which was facilitated by shared intentionality from others that was easily communicated through language. Language allowed subordinates to collaborate, coordinating plans to dampen the attempt at dominance by the instigator. Over time, this resulted in the selection against reactive aggression.^[17]

Theoretical criticism

The self-domestication hypothesis has been met with some degree of criticism. Some researchers have argued that the human brain is peramorphic, instead of paedomorphic. Wrangham puts forth that these arguments do not address the evolution of Homo sapiens from their most recent ancestor, instead focusing too heavily on a direct contrast between apes and humans.^[18]

Related Research Articles

<i>Ardipithecus</i> Extinct genus of hominins

Ardipithecus is a genus of an extinct hominine that lived during the Late Miocene and Early Pliocene epochs in the Afar Depression, Ethiopia. Originally described as one of the earliest ancestors of humans after they diverged from the chimpanzees, the relation of this genus to human ancestors and whether it is a hominin is now a matter of debate. Two fossil species are described in the literature: A. ramidus, which lived about 4.4 million years ago during the early Pliocene, and A. kadabba, dated to approximately 5.6 million years ago. Initial behavioral analysis indicated that Ardipithecus could be very similar to chimpanzees, however more recent analysis based on canine size and lack of canine sexual dimorphism indicates that Ardipithecus was characterised by reduced aggression, and that they more closely resemble bonobos.

Bipedalism is a form of terrestrial locomotion where a tetrapod moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped, meaning 'two feet'. Types of bipedal movement include walking or running and hopping.

Human evolution is the evolutionary process within the history of primates that led to the emergence of Homo sapiens as a distinct species of the hominid family that includes all the great apes. This process involved the gradual development of traits such as human bipedalism, dexterity, and complex language, as well as interbreeding with other hominins, indicating that human evolution was not linear but weblike. The study of the origins of humans, also called anthropogeny, anthropogenesis, or anthropogony, involves several scientific disciplines, including physical and evolutionary anthropology, paleontology, and genetics.

Homininae, also called "African hominids" or "African apes", is a subfamily of Hominidae. It includes two tribes, with their extant as well as extinct species: 1) the tribe Hominini ―and 2) the tribe Gorillini (gorillas). Alternatively, the genus Pan is sometimes considered to belong to its own third tribe, Panini. Homininae comprises all hominids that arose after orangutans split from the line of great apes. The Homininae cladogram has three main branches, which lead to gorillas, and to humans and chimpanzees via the tribe Hominini and subtribes Hominina and Panina. There are two living species of Panina and two living species of gorillas, but only one extant human species. Traces of extinct Homo species, including Homo floresiensis have been found with dates as recent as 40,000 years ago. Organisms in this subfamily are described as hominine or hominines.

The bonobo, also historically called the pygmy chimpanzee, is an endangered great ape and one of the two species making up the genus Pan. While bonobos are, today, recognized as a distinct species in their own right, they were initially thought to be a subspecies of Pan troglodytes, due to the physical similarities between the two species. Taxonomically, the members of the chimpanzee/bonobo subtribe Panina—composed entirely by the genus Pan—are collectively termed panins.

The origin of language, its relationship with human evolution, and its consequences have been subjects of study for centuries. Scholars wishing to study the origins of language must draw inferences from evidence such as the fossil record, archaeological evidence, contemporary language diversity, studies of language acquisition, and comparisons between human language and systems of communication existing among animals. Many argue that the origins of language probably relate closely to the origins of modern human behavior, but there is little agreement about the facts and implications of this connection.

Neanderthals became extinct around 40,000 years ago. Hypotheses on the causes of the extinction include violence, transmission of diseases from modern humans which Neanderthals had no immunity to, competitive replacement, extinction by interbreeding with early modern human populations, natural catastrophes, climate change and inbreeding depression. It is likely that multiple factors caused the demise of an already low population.

The evolution of human intelligence is closely tied to the evolution of the human brain and to the origin of language. The timeline of human evolution spans approximately seven million years, from the separation of the genus Pan until the emergence of behavioral modernity by 50,000 years ago. The first three million years of this timeline concern Sahelanthropus, the following two million concern Australopithecus and the final two million span the history of the genus Homo in the Paleolithic era.

<span class="mw-page-title-main">Hominini</span> Tribe of mammals

The Hominini form a taxonomic tribe of the subfamily Homininae ("hominines"). Hominini includes the extant genera Homo (humans) and Pan and in standard usage excludes the genus Gorilla (gorillas).

Richard Walter Wrangham is an English anthropologist and primatologist; he is Professor of Biological Anthropology at Harvard University. His research and writing have involved ape behavior, human evolution, violence, and cooking.

Australopithecina or Hominina is a subtribe in the tribe Hominini. The members of the subtribe are generally Australopithecus, and it typically includes the earlier Ardipithecus, Orrorin, Sahelanthropus, and (sometimes) Graecopithecus. All these closely related species are now sometimes collectively termed australopiths or homininians. They are the extinct, close relatives of modern humans and, together with the extant genus Homo, comprise the human clade. Members of the human clade, i.e. the Hominini after the split from the chimpanzees, are now called Hominina.

Archaic humans is a broad category denoting all species of the genus Homo that are not Homo sapiens. Among the earliest related remains are those from Jebel Irhoud in Morocco, Florisbad in South Africa (259 ka), and Omo-Kibish I in southern Ethiopia. The term typically includes H. antecessor (1200–770 ka), H. bodoensis (1200–300 ka), H. heidelbergensis (600–200 ka), Neanderthals, H. rhodesiensis (300–125 ka) and Denisovans,

The Middle Awash is a paleoanthropological research area in the northwest corner of Gabi Rasu in the Afar Region along the Awash River in Ethiopia's Afar Depression. It is a unique natural laboratory for the study of human origins and evolution and a number of fossils of the earliest hominins, particularly of the Australopithecines, as well as some of the oldest known Olduwan stone artifacts, have been found at the site—all of late Miocene, the Pliocene, and the very early Pleistocene times, that is, about 5.6 million years ago (mya) to 2.5 mya. It is broadly thought that the divergence of the lines of the earliest humans (hominins) and of chimpanzees (hominids) was completed near the beginning of that time range, or sometime between seven and five mya. However, the larger community of scientists provide several estimates for periods of divergence that imply a greater range for this event, see CHLCA: human-chimpanzee split.

Ardipithecus ramidus is a species of australopithecine from the Afar region of Early Pliocene Ethiopia 4.4 million years ago (mya). A. ramidus, unlike modern hominids, has adaptations for both walking on two legs (bipedality) and life in the trees (arboreality). However, it would not have been as efficient at bipedality as humans, nor at arboreality as non-human great apes. Its discovery, along with Miocene apes, has reworked academic understanding of the chimpanzee–human last common ancestor from appearing much like modern-day chimpanzees, orangutans and gorillas to being a creature without a modern anatomical cognate.

The Hominidae, whose members are known as the great apes or hominids, are a taxonomic family of primates that includes eight extant species in four genera: Pongo ; Gorilla ; Pan ; and Homo, of which only modern humans remain.

The chimpanzee–human last common ancestor (CHLCA) is the last common ancestor shared by the extant Homo (human) and Pan genera of Hominini. Estimates of the divergence date vary widely from thirteen to five million years ago.

Changes to the dental morphology and jaw are major elements of hominid evolution. These changes were driven by the types and processing of food eaten. The evolution of the jaw is thought to have facilitated encephalization, speech, and the formation of the uniquely human chin.

The diet of known human ancestors varies dramatically over time. Strictly speaking, according to evolutionary anthropologists and archaeologists, there is not a single hominin Paleolithic diet. The Paleolithic covers roughly 2.8 million years, concurrent with the Pleistocene, and includes multiple human ancestors with their own evolutionary and technological adaptations living in a wide variety of environments. This fact with the difficulty of finding conclusive evidence often makes broad generalizations of the earlier human diets very difficult. Our pre-hominin primate ancestors were broadly herbivorous, relying on either foliage or fruits and nuts and the shift in dietary breadth during the Paleolithic is often considered a critical point in hominin evolution. A generalization between Paleolithic diets of the various human ancestors that many anthropologists do make is that they are all to one degree or another omnivorous and are inextricably linked with tool use and new technologies. Nonetheless, according to the California Academy of Sciences, "Prior to about 3.5 million years ago, early humans dined almost exclusively on leaves and fruits from trees, shrubs, and herbs—similar to modern-day gorillas and chimpanzees."

Domestication syndrome refers to two sets of phenotypic traits that are common to either domesticated plants or domesticated animals.

<i>Survival of the Friendliest</i> 2020 non-fiction book by Hare & Woods

Survival of the Friendliest: Understanding Our Origins and Rediscovering Our Common Humanity is a book by anthropologist Brian Hare and writer Vanessa Woods, first published in 2020, based on Hare's research hypothesis of human self-domestication. The main thesis of the book is that late in human evolution Homo sapiens underwent a process of extreme selection for friendliness that led to the self-domestication syndrome, as seen in other animals. The self-domestication syndrome led to a series of cognitive changes that allowed modern humans to out compete other species of humans in the Pleistocene, including Neanderthals, and become the most successful mammal on the planet. Hare and Woods argue that self-domestication is an ongoing process that continues today.

References

1 2 Zanella, Matteo; Vitriolo, Alessandro; Andirko, Alejandro; Martins, Pedro Tiago; Sturm, Stefanie; O’Rourke, Thomas; Laugsch, Magdalena; Malerba, Natascia; Skaros, Adrianos; Trattaro, Sebastiano; Germain, Pierre-Luc; Mihailovic, Marija; Merla, Giuseppe; Rada-Iglesias, Alvaro; Boeckx, Cedric (2019-12-06). "Dosage analysis of the 7q11.23 Williams region identifies BAZ1B as a major human gene patterning the modern human face and underlying self-domestication". Science Advances. 5 (12). eaaw7908. doi:10.1126/sciadv.aaw7908. ISSN 2375-2548. PMC 6892627 . PMID 31840056.
↑ Theofanopoulou, Constantina; Gastaldon, Simone; O’Rourke, Thomas; Samuels, Bridget D.; Messner, Angela; Martins, Pedro Tiago; Delogu, Francesco; Alamri, Saleh; Boeckx, Cedric (2017-10-18). "Self-domestication in Homo sapiens: Insights from comparative genomics". PLOS ONE. 12 (10): e0185306. Bibcode:2017PLoSO..1285306T. doi: 10.1371/journal.pone.0185306 . ISSN 1932-6203. PMC 5646786 . PMID 29045412.
↑ Shilton, D; Breski, M; Dor, D; Jablonka, E (February 14, 2020). "Human Social Evolution: Self-Domestication or Self-Control?". Frontiers in Psychology. 11: 134. doi: 10.3389/fpsyg.2020.00134 . PMC 7033472 . PMID 32116937.
↑ https://www.youtube.com/watch?v=acOZT240bTA&ab_channel=UniversityofCaliforniaTelevision%28UCTV%29 Harvard Prof Richard Wrangham
1 2 Sauer, Hanno (2023). La invención del bien y del mal. Paidós. ISBN 9788449340963.
↑ Hawks, John (2019). "The Goodness Paradox" Review: The Benefits of Good Breeding (book review)" (Wall Street Journal ed.).
↑ Goldman, Jason (6 September 2010). "Man's new best friend? A forgotten Russian experiment in fox domestication". Scientific American. Retrieved 23 May 2014.
↑ Wilkins, Adam S; Wrangham, Richard W; Fitch, W Tecumseh (2014-07-01). "The "Domestication Syndrome" in Mammals: A Unified Explanation Based on Neural Crest Cell Behavior and Genetics". Genetics. 197 (3): 795–808. doi:10.1534/genetics.114.165423. ISSN 1943-2631. PMC 4096361 . PMID 25024034.
↑ Anastasiadi, Dafni; Piferrer, Francesc (2019-10-01). Wittkopp, Patricia (ed.). "Epimutations in Developmental Genes Underlie the Onset of Domestication in Farmed European Sea Bass". Molecular Biology and Evolution. 36 (10): 2252–2264. doi: 10.1093/molbev/msz153 . ISSN 0737-4038. PMC 6759067 . PMID 31289822.
↑ "Universidad de Barcelona". Primera demostración experimental de la hipótesis de la autodomesticación del ser humano. 5 December 2019.
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1 2 Clark, Gary; Henneberg, Maciej (2017). "Ardipithecus ramidus and the evolution of language and singing: An early origin for hominin vocal capability". HOMO: Journal of Comparative Human Biology. 68 (2): 101–121. doi:10.1016/j.jchb.2017.03.001. PMID 28363458.
↑ Bednarik, Robert G. (2008). "The Domestication of Humans". Anthropologie. 46 (1): 1-17.
↑ Bednarik, Robert G. (2011). The Human Condition. Springer, New York, pp. 127-141. ISBN 978-1-4419-9352-6.
↑ Wrangham, Richard W. (2021). "Targeted conspiratorial killing, human self-domestication and the evolution of groupishness". Evolutionary Human Sciences. 3: e26. doi: 10.1017/ehs.2021.20 . ISSN 2513-843X. PMC 10427284 . PMID 37588548. S2CID 233029730.
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1 2 3 Wrangham, R. W. (2018). Two types of aggression in human evolution. Proceedings of the National Academy of Sciences - PNAS, 115(2), 245-253.
↑ Steele, T. E., and Weaver, T. D. (2014). Comment on Cieri et al. Craniofacial feminization, social tolerance, and the origins of behavioral modernity. Curr. Anthropol. 55, 434–435. : doi: 10.1086/677209

v t e Domestication of animals
Vertebrates	Alpaca Bactrian camel Bali cattle Cat Cattle Chicken Dog Donkey Dromedary Domestic duck Domestic Muscovy duck Ferret Gayal Goat Guinea pig Horse Llama Domestic pig Fancy mouse Poultry Domestic rabbit Reindeer Sheep Domesticated silver fox Water buffalo Yak Zebu
Invertebrates	Honey bee Silkworm
History	Domestication of the cat cats in ancient Egypt Domestication of the dog Domestication of the goat Domestication of the Syrian hamster Domestication of the horse theories Domesticated animals of Austronesia Domestication of the sheep
Related topics	List of domesticated animals Selective breeding Self-domestication The Variation of Animals and Plants Under Domestication Genomics of domestication