Is the domestication syndrome a myth?

In most if not all of my posts on domestication and dedomestication I mentioned the concept of the domestication syndrome that says that domestication works by the same mechanisms and has the same effects in any species that was domesticated. Domestic animals share certain traits, which are that eye-catching that it seems very intuitive that the domestication syndrome as such exists. Parts of my dedomestication hypothesis are based on the assumption that there is a domestication syndrome. However, the concept has been called into question in several works. 

The domestication syndrome is the assumption that all domestic animals, mammals in particular, share certain phenotypic traits, both behavioural and morphological. These include paedomorphy in behaviour and morphology, a reduced brain volume, reduced sexual dimorphism, piebald or spotted coat colour patterns, loss of seasonal adaptions, increased reproductive rate, earlier maturity and others. The hypothesis was expanded in publications discussing the findings of the famous Farm fox experiment, namely that artificial selection on tameness alone produced many of the typically domestic traits as a by-product, suggesting that there is a connecting mechanism working during domestication. You can read my post that I linked above for more detail and literature references on that. 

 

The validity of the Farm fox experiment as evidence for the domestication syndrome is called into question in some sources. For example, the alleged cranial shortening in the foxes selected on tameness is based on anecdotical evidence, it turned out that they are not distinguishable from wild foxes in cranial morphology [1]. A brain volume reduction has not been detected in selected foxes [1]. White spotting in the colour that has been said to be a by-product of the selection on tameness is also found in the control group and the foxes selected on increased aggression [2]. However, the white spotting is more common in the foxes selected on tameness than in the other groups [1]. Nevertheless, a spotted coat colour and a curved tail (the latter trait found in 10% of the foxes selected on tameness), is not associated with increased tameness in the individuals [1]. Lord et al. state that due to the limited population size of the starting population, it is possible that shifts in allele frequency were caused by “chance alone” [1], therefore morphological changes in the selected foxes do not necessarily have to be caused by selection on tameness according to the authors [1]. 

However, there seems to be a weak correlation between tame behaviour and white spotted coat colours in rats and foxes [3]. It has been found, interestingly, that there is no correlation between several physical characters considered symptoms of the domestication syndrome (f.e. floppy ears, spotted coat colours) among each other, and with behaviour among dogs [4]. This seems to be contradictory to what would be expected by a very strict application of the domestication syndrome hypothesis. Also, mutations causing piebald coat colour patterns also appear in wild animals. It is not all that rare in several deer species, for example moose in North America: 

If the piebald coat colour patterns in domestic animals are strongly connected to tameness, it would have to be expected that these moose are also less fearful towards humans than their “normally” coloured conspecifics. This assumption would have to be tested. 

There is a paper by Lord et al. that calls brain volume reduction as a consequence of domestication into question [5]. However, the reduction of brain volume is well-documented for many domesticated species [6], and has recently also been found to be the case in cattle compared to the aurochs [7]. Another problem is that the paper by Lord et al. adopts the premature conclusion by Gaunitz et al. 2018 that the Przewalski’s horse is feral and “not wild in any sense” [6], while they consider the feral European mouflon a wild animal to compare sheep against [6]. So they consider a wild animal feral and a feral animal wild, what is a bit of a problem in the argumentation. 

A major component of the hypothesis that selection on behaviour results in alterations of physical appearance is the proposal that neural crest cell genes are affected by selection on tameness [2,8]. The neural crest is a precursor of many cell types in vertebrates, pigment cells among them. The hypothesis says that if the genes of neural crest cells are affected by selection on tameness, the migration of the precursors of pigment cells is distorted, causing irregular unpigmented areas on the body, resulting in the piebald coat colour that is seen in many domestic animals. A very recent paper compared neural crest genes of domestic animals of several species and compared it to the respective wildtypes or animals related to the wildtype (bison were used to compare with domestic cattle, for example). The result was that evidence for positive selection on neural crest genes was found in nearly all cases [8], providing support for the hypothesis that alterations of the genes of the neural crest played a role in domestication of the species that have been domesticated [8]. Interestingly, in the Farm fox experiment it was noted that crossing two white-marked foxes would occasionally produce offspring that held their head askew [1]. I think it is possible that the allele(s) producing these white markings are connected to factors detrimental for the development of the nervous system, what would support the neural crest hypothesis, although other explanations are plausible as well (f.e. asymmetric development of musculature, abnormities in the vestibular system) – that phenomenon deserves further investigation in my opinion. 

Domestication goes hand in hand with an increase of deleterious alleles as a result of mutation accumulation since natural selection plays no or only a minor role in domesticates. This phenomenon is described as the “costs of domestication” [9]. Mutation accumulation might be an alternative explanation for why piebald coat colour patterns are found in all domesticated species. Rather than being connected to behavioural aspects that get selected for during domestication, it is possible that these piebald patterns showed up due to spontaneous mutations that also appear in wild populations, and humans tended to favour these deviant colour variants in their breeding regime. In fact, piebald patterns are only one type of novel colours that appear in domestic populations. Many domesticated species show melanism (found in cattle, dogs, horses, cats and others), erythricism, leucism and albinism as much as completely novel coat colours, yet nobody suggested that these pigment modifications are a common consequence of domestication and possibly connected to behavioural traits (with the exception of melanism, which has been linked to increased aggression in the past). Piebald patterns even exist in “domesticated” fish such as the goldfish, and as far as I know goldfish were never particularly selected for tameness. The fact that white markings are more common in the foxes selected on tameness than in the other lineages can also be due to genetic drift or the loci regulating those markings being coincidentally genetically linked with those regulating tameness on the same chromosome. Therefore, white spots do not necessarily have to be a consequence of behavioural modifications during domestication.

While white spotted patterns are not a good example for the connection between physical characteristics and behaviour and the role of this possible connection in domestication, I would not give up that hypothesis. We should not forget that paedomorphy and a reduced brain volume are very common among domestic animals, and that changes in hormone productions likely played a role in domestication. Thyroid hormones have a major role in postnatal growth, pigmentation, brain development, adrenal gland function and development of the gonads [10]. Selection on tameness is, to a certain degree, selection on paedomorphic behaviour as the fear response of juvenile mammals is much less intense than that of fully grown ones. Therefore, selection on tameness might have influenced the overall development, causing the expression of hormones relevant in adulthood to be delayed. This would lead to an overall paedomorphy because it would affect thyroid hormones, among others (corticosteroids might play a role as well). If the consequence is a shortage in thyroid production, this would have a dramatic influence on the morphology of the animals. For example, hypothyroidic rats are smaller, have a shorter snout and floppy ears – they have paedomorphic, domestic characters. Hypothyroidism is also known to cause cretinism in humans, which includes symptoms such as shortened extremities, reduced body size and lowered cognitive abilities. This is what we see in many domestic animals. I also think that hormonal changes are responsible for the brain volume reduction, perhaps even the thyroid hormones, rather than the fact that a domestic life is less cognitively demanding than a life in the wild, what is usually offered as explanation for the smaller brains of domesticates. We should also not forget that the neural crest genes of domesticates show signs of positive selection as outlined above, although pleiotropic effects leading to a change in physical appearance have not been proven directly yet. 

I think the domestication syndrome concept would be invalidated if there was a domesticated species that is completely devoid of any traits that are considered symptoms of the domestication syndrome such as paedomorphy, reduced brain volume and others, yet still behaves completely domestic, i.e. has a very moderate fear response, reduced aggression and increased tameness compared to its wildtype, trainability and agreeableness. Sixteen mammal species have been domesticated, yet there is no such case. This indicates to me that the domestication syndrome is a valid concept, although piebald colour patterns possibly have to be excluded from the list of symptoms considering the weak to absent correlation between them and tameness. 

 

Literature

 

[1] Lord et al.: The history of Farm foxes undermines the animal domestication syndrome. 2019. 

[2] Wilkins: A striking example of developmental bias in an evolutionary process: the “domestication syndrome”. 2019 

[3] Wilkins et al.: The “domestication syndrome” in mammals: A unified explanation based on neural crest cell behaviour and genetics. 2014

[4] Wheat et al.: Morphology does not covary with predicted behavioral correlations of the domestication syndrome in dogs. 2020. 

[5] Lord et al.: Brain size does not rescue domestication syndrome. 2020. 

[6] Balcarcel et al.: The mammalian brain under domestication: discovering patterns after a century of old and new analyses. 2021. 

[7] Balcarcel et al.: Intensive human contact correlates with smaller brains: differential brain size reduction in cattle types. 2021. 

[8] Rubio: Neural crest cell genes and the domestication syndrome: A comparative analysis of selection. 2022. 

[9] Moyers et al: Genetic costs of domestication and improvement. 2017. 

[10] Dobney & Larson: Genetics and animal domestication: new windows on an elusive process. 2005

Extinct megafauna that could be revived using genome editing

Humans wiped out countless species of animals. Some of those species, particularly those that died out comparably recently, might actually be retrievable. Usually, cloning comes to mind when talking about reviving extinct animals. However, somatic nucleus transfer for reproductive cloning requires an intact cell and not just the DNA of the animal, which is why it is not available for most species wiped out by man. However, there are a few megafaunal species that have been wiped off from which we have at least one and in some cases several complete genomes. If there is a still extant species that is closely related and would make a suitable surrogate, it would be possible to exchange the alleles specific for species A with those for species B and thus creating a viable cell with the genome of the extinct species in question with genome editing. This limits the number of extinct animals that could be revived. For example, I would imagine it to be pretty difficult if not impossible for a species like the thylacine, which has been evolutionary separated for 30 million years from its closest living relatives. In some cases, it could be easy and much less effortful because of the lower number of genes that differ and the suitability of the surrogate because the animal has a very close living relative. In this post, I present a number of megafaunal species from which full genomes either have been acquired or at least could potentially be acquired and which have a more or less closely related relative that can be used for genome editing and as a surrogate. The mitochondrial DNA of the resulting animal would be that of the donor cell, which would be from the related species. However, as mitochondrial genes are highly conserved among mammals this would not have much of an influence. Using closely related species also has the advantage that the behaviour will be rather similar, especially among the large herbivore species that I am going to list. This makes the rearing by a surrogate mother and socialization of the result less problematic or maybe not even an issue at all. 

I see reviving an extinct animal that has been wiped out by man as a contribution to species conservation just as breeding an endangered species or subspecies. One might ask, particularly in the case of wiped-out subspecies, why doing that at all if there are suitable ecological proxies. Occasionally some even question the need to conserve endangered subspecies such as the Northern White rhino because their conspecifics from other subspecies would function ecologically the same or very similar. Personally, I cannot relate to that mindset. Conservation is about preserving biodiversity and the preservation of evolutionary more or less distinct subspecies is a vital part of that. The same goes for reviving extinct species or subspecies – it would greatly increase the biodiversity again, after it has been depleted by man when the species or subspecies was wiped out. 

 

Bubal hartebeest, Alcelaphus buselaphus  

This animal is sometimes also considered a subspecies, but that question is merely taxonomical and not relevant for “de-extincting” the animal. In any case, other members of Alcelaphus could be used for genome editing and as a surrogate. Many individuals must have been preserved as trophies, and it is potentially possible to acquire full nuclear genomes from them. 

 

Bluebuck, Hippotragus leucophaeus  

Other members of Hippotragus could be used as a surrogate and for genome editing. It can be tried to acquire a fully nuclear genome from taxidermies.  

 

European aurochs, Bos primigenius primigenius

One full nuclear genome has been resolved in 2015 from a well-preserved Neolithic bone. Considering the richness of recent aurochs material, it could be possible to obtain quite a few more complete genomes. And there is a very close living relative, modern cattle. The number of genes that would have to be exchanged would probably be lower than in most of the other cases I am listing here, and also the surrogate and the procedure of implanting an embryo would be completely unproblematic. And considering the similarities in behaviour between cattle and aurochs, socialization will not be problematic either. For these reasons, I consider the aurochs one of the most realistic candidates for a revival through genome editing. Even if the resolved genome remains the only one to be fully resolved, one revived aurochs individual still can be outbred using aurochs-like cattle. I wrote a post on that a few years ago. 

 

Several types of wild horses 

There are well-preserved mummies of Siberian wild horses, Equus caballus lenensis, and one of the Yukon wild horse, Equus caballus lambei, so it could be possible to obtain fully resolved nuclear genomes from that. A domestic horse could be used for genome editing and as a surrogate. Even if only one genome can be obtained, the revived horses can be outbred with Przewalski’s horses and/or robust landraces in the same manner as I suggested for revived aurochs. 

 

Kouprey, Bos sauveli  

Numerous kouprey specimen have been preserved as trophies and one skin. It could be possible to obtain full nuclear genomes from that very recent material. The closest living relative is the Cambodian banteng which hybridized with the kouprey in the past. It can be used for genome editing, as a surrogate and even for outbreeding if necessary. 

 

Quagga, Equus quagga quagga  

The quagga is not and cannot be bred-back from extinction with living Plains zebras, which is why it would be desirable to try to acquire full genomes from the numerous preserved skins and the few skeletal material that is preserved of this zebra. The zebras of the Quagga Project can be used for genome editing, as a surrogate and outbreeding if necessary. 

 

Pyrenean ibex, Capra pyrenaica pyrenaica  

This is the only extinct animal that has been cloned so far, unfortunately the clone died shortly after birth. Genome editing with individuals from other subspecies of Capra pyrenaica could be more successful, they can be used as surrogates and for outbreeding. 

 

Steppe bison, Bos (Bison) priscus  

There are plentiful of remains from steppe bison, including soft tissue. Perhaps it would be possible to obtain full nuclear genomes from that. Needless to say, that still existing bison, be it European or American, can be used for genome editing, as a surrogate and outbreeding. 

 

? Woolly mammoth, Mammuthus primigenius  

Currently, there is no de-extinction project in the strict sense focusing on the woolly mammoth. There is the attempt to create a “mammophant” by introducing mammoth alleles for certain traits into the genome of an Asian elephant, what is not what I would consider de-extinction in the strict sense. If doing that is possible, it might also be possible even if more effortful, to exchange all alleles of genes where Asian elephant and woolly mammoth differ. However, since implanting an embryo into an elephant is very complicated, and those who want to create plan to use an artificial womb, a technique which does not exist hitherto, I wonder if it is feasible to recreate the woolly mammoth for practical reasons. 

 

Caucasian Wisent, Bos (Bison) bonasus caucasicus  

Several skins and trophies of this wiped-out subspecies (or species or variety, there is no consensus on its taxonomic status) exist, so it could be possible to obtain full nuclear genomes from it. European bison of the Lowland-Caucasus line, which partly descend from the last Caucasian wisent bull, could be used for genome editing, as a surrogate and for outbreeding. Obtaining genomes from remains of wisent prior to the bottleneck in the 20^th century could also help to greatly increase the very limited genetic diversity of this endangered bovine. 

 

Cave lion, Panthera spelaea  

Several very well-preserved pubs of this feline have been found. It might be possible to acquire full nuclear genomes from that, and the closely related actual lion would be suitable for genome editing and as a surrogate. 

 

Schomburgk’s deer, Rucervus schomburgki  

Some remains of this deer species exist, a sister species from the Rucervus clade could be used for genome editing and as a surrogate. 

 

Japanese sea lion, Zalophus japonicus

There are taxidermied specimens of this sea lion, related species of the Zalophus clade can be used for genome editing, as a surrogate and possibly outbreeding if necessary. 

 

Caribbean monk seal, Neomonachus tropicalis

There should be some remains of this recently extinct species, the related Hawaiian monk seal can be used for genome editing, as a surrogate and possibly outbreeding if necessary. 

 

One common objection against the revival of extinct animals is “one individual is not enough to build a population”. Apart from the fact that even one individual could tell us a lot about the extinct animal species/subspecies, it could be possible to get several genomes of those recently extinct species. Getting the full genome of five or ten individuals from different regions and times would probably enable to get a genetic diversity comparable to that of the modern wisent population, which descends from only twelve founding individuals from the same population. Some wisent individuals show inbreeding-related problems, but not to the extent that it threatens the survival of the species. An even more extreme example would be the Mauritius kestrel. Apart from that, related species/subspecies can always be used for outbreeding to add genetic diversity. Hybridization among related species with neighboring or overlapping distributions is very common in the animal kingdom. 

 

The colour of Indian aurochs cows

We know nothing about the colour of the Indian aurochs with certainty, except for the fact that it must have had the E⁺ allele on the Extension locus, because the majority of zebus have it and it is also found in taurine cattle, suggesting that it was already present in the common ancestor of the primigenius and namadicus lineages. That means namadicus must have had the colour that has both phaeomelanin and eumelanin (red and black pigment), dispersed in some pattern across the pelage, a white muzzle ring and testosterone-dependent eumelanisation. Very likely sexual dichromatism was present, i.e. that bulls and cows had different colours. Some zebu breeds have retained a certain degree of sexual dichromatism, with the bulls being slightly darker than the cows. The colour of the cows is in the focus of this post. 

Many zebu cows that have the production of phaeomelanin enabled (the mutation disabling the production of red pigment is quite common among zebus and perhaps originated in that lineage) are almost homogeneously reddish-orangish-brown, with a dark brown dorsal stripe (that is not always present), lightly coloured rings around the eye and a lightly coloured area on the ventral side of the trunk and the inner side of the limbs. Black or very dark areas are (almost) absent. A colour consisting of a reddish-brown base colour with a dark dorsal stripe is sometimes also found in taurine cows, albeit rarely. It is much more common in zebu cows. The only black or very dark areas in zebus having that colour are, if present, along the anterior side of the forequarters, either down to the carpals or to the toes. I consider it quite likely that this is the original colour of female Indian aurochs cows and it can be seen in breeds like Red Kangayam. 

The reason for my assumption is that female Java banteng have a very, very similar colour. They are orangish-reddish-brown, with a dark dorsal stripe, lightly coloured areas on the inner side of the limbs and the ventral side of the trunk, they even have the dark areas on the forelimb, except for the part that is completely devoid of pigments. In fact, if those white “socks” and buttocks were not there, the colour would be almost identical. I see two possible explanations for that similarity: a) the common ancestor of both species had this colour and it is the ancestral trait, thus was also present in the Indian aurochs b) introgression from banteng into the zebu after domestication. As for the latter possibility, the introgression of banteng or their domesticated form Bali cattle is documented for some lineages of zebus. But I consider it less likely that this is the reason for the similarity in coat colour as in this case this colour would not be found in taurine cattle too, which it is, albeit rarely. Also, Red Kangayam are found in Southern India, where banteng introgression is less likely for geographic reasons. This makes the assumption that it is inherited from a common ancestor more likely, since such a close similarity in more or less closely related species is probably not a coincidence. If this colour was already present in the common ancestor of the Java banteng and the zebu, it is the most parsimonious assumption that it was present already in the Indian aurochs. That colour is in fact not all too special. Wildtype coloured calves in taurine and indicine cattle are usually reddish brown with a dark dorsal stripe, the cows retaining this dark dorsal stripe and having almost no black or dark brown areas just means that the process of growing what is the adult coat colour in bulls is stopped earlier than in European aurochs cows, which often had black heads, necks and legs or were even black with a red colour saddle, as cave paintings show. 

However, this colour being the result of banteng introgression into zebus after domestication cannot be ruled out completely, and in the lack of artistic depictions showing the Indian aurochs and the fact that female zebu appear in a wide variety of colours we can only guess what its colour was like. I think the colour shown by the Red Kangayam is a very plausible one for namadicus cows, but this has to remain a speculation, as long as we do not have any direct evidence of the coat colour of the Indian aurochs. 

 

Are domestic cattle truly smaller than the aurochs?

The question in the headline of this post will immediately be answered with “yes, obviously” by most people, which is understandable as the European aurochs is known for being a very large bovine and the size reduction is one of the most noticeable consequences of domestication in cattle. However, there is one aspect that should be considered. 

It starts with how to define body size. In mammals, one of the most widely used parameter of body size is the withers height. Going by this factor, it is obvious that the aurochs was much larger than most domestic cattle – very large breeds like Chianina or Bhagnari being the exception. Go here for my post on how large the largest aurochs might have been.

When naming the largest living land animal, most people will say it is the African elephant. This is because it is the heaviest terrestrial animal. But going by height, it would be giraffes, and going by length, the reticulated python would be the second-largest terrestrial animal on earth. Yet, those species are rarely considered the largest terrestrial animals. So, is mass the most important body size parameter? It is certainly an objective one, as it is almost independent of the morphology and bauplan of the animals (with the exception of birds which have an air sac system and pneumatized bones, which is why their bodies have a lower density than those of other terrestrial animals). If we go only by mass, let’s examinate if cattle are truly smaller than aurochs. 

One problem is that we do not know the exact weight of aurochs. No aurochs were weighted, so we can only guess by using extant wild bovines as a comparison. Since the males are larger than the females in bovines, I only refer to the mass of males in this post. Perhaps the weight of the aurochs was somewhere in the range of banteng, wisent and wild yaks, which would be between 700 and 1000 kg. Wild yaks have a slightly more elongated and more robust morphology than the aurochs had, but have a similar height compared to the largest aurochs (which is roughly 2 metres) and their weight is around 1000 kg. While yaks are built slightly more massive than aurochs, they have a higher shoulder hump, what influences the withers height. So it could in sum be that a 200 cm tall aurochs was roughly the same weight as a 200 cm wild yak. That would mean that a 160 cm aurochs had only about 510 kg. The wisent has similar proportions and a roughly similar build. The record for wisent height is 188 cm, for the weight it is 840 kg in wild-living animals. That means a 2 m wisent would be 1011 kg and a 160 cm wisent would be around 500 kg. Banteng reach up to 190 cm and 900 kg weight, which would be 529 kg in a 160 cm banteng. Since all those three bovines result in a similar weight range, maybe it is reasonable to assume a weight of around 500 kg for a 160 cm aurochs, and 1000 kg and slightly above for a 200 cm aurochs. Keep in mind that weight increases with x³ while height only with x. Those are only very rough estimates, and the weight would also depend on the individual condition of the animal and the season. 

What is interesting now is that many domestic bulls surpass the possible weight of the largest aurochs. Bulls with a weight of over 1000kg are actually not a rarity in breeds of a medium height. For comparison, the Taurus bull Lucio had a withers height of 165 cm and a weight of 1400 kg. A 165 cm tall aurochs bull would, if the estimation above is correct, weigh around 500 kg. So the Taurus bull has more than twice the mass of an aurochs with the same height. That is due to the different morphology: domestic cattle mostly have shorter legs and a longer trunk, plus a smaller hump as much as a way bulkier trunk, especially the intestines are enlarged. This results in a higher weight relative to the withers height.  

Lucio the Taurus bull (Sayaguesa x Heck)

The morphology of cattle drastically changed during domestication: the legs became shorter, the trunk longer, the intestines larger, the head smaller, the hump smaller et cetera. This led to a dramatic height decrease, while the mass was not that much affected. Surely there are dwarf cattle breeds that are lighter in weight than the aurochs probably was, especially during the Bronze age there were tiny cattle that were about the size of a sheep. But as far as the average modern day cattle body size is concerned, cattle lost height during domestication but not necessarily mass. In some cases, mass was even gained compared to the aurochs. 

So, if mass would be the only parameter for body size, then most domestic cattle are not necessarily smaller than the aurochs, it is their morphology that changed dramatically. 

The dingo: a post-domestic wild animal?

Long-term readers of my blog will be familiar with my dedomestication hypothesis that I proposed in the dedomestication series. The term dedomestication is not very established in scientific literature yet, but there can be now doubt that natural selection will change domestic animals that have returned into the wild. This evolutionary process would result in what I call a post-domestic wildtype, opposed to a predomestic wildtype. This post-domestic wildtype would be just as wild as any other wild animal, with the difference that it descends from a domestic population. 

I proposed that this post-domestic wildtype is not necessarily a revert to the original predomestic wildtype, but that it depends on the selective pressures in the respective environment, genetic drift and also that novel traits can be beneficial, especially in a new environment. As I write in my dedomestication series, the hypothesis has empirical problems. For once, feral domestic animals are understudied in terms of possible evolutionary changes they experience. And moreover, there are hardly any feral domestic populations that have been living in the wild under natural selection for a considerable time span sufficient for evolutionary changes to become visible and at the same time reproductively isolated from backcrossing with wild or domestic animals. For example, feral pigs in North America (razorbacks) sometimes greatly resemble the Eurasian wild boar, what would endorse one of the main proposals of the dedomestication hypothesis (namely that wildtype traits tend to have a higher evolutionary fitness and thus the feral population starts to resemble the original wildtype on adaptive traits). The problem is, however, that these feral pigs often hybridized with wild boar that have been introduced there as well, what explains the resemblance between the two. 

Nevertheless, I see two possible candidates for a post-domestic wildtype because of a considerable time span they have been reproductively isolated and exposed to natural selection: the dingo and the European mufflon. This post is going to focus on the dingo. But first of all, it is essential to define which criteria an animal would have to fit if it was to be considered a post-domestic wildtype. 

 

A definition of the post-domestic wildtype

 

The most abstract definition of a post-domestic wild animal would be that its biology is entirely shaped by natural selection and not artificial selection. In detail, this would mean: 

- It is devoid of typical signs of domestication: paedomorphy in behaviour and morphology, earlier maturity, loss of seasonal adaptions, white spotted patterns in the colour or other detrimental colour mutations, reduced brain volume, reduced sexual dimorphism

- It is adapted to the biotic and abiotic factors of its environment 

- It is more or less homogeneous in its biology, especially regarding adaptive characters 

The exact time span of how long the animal has been subject to natural selection is technically of limited relevance, because the speed at which evolutionary changes become evident depends on how genetically diverse the starting gene pool is – this is known as Fisher’s fundamental theorem and it describes that changes in allele frequency occur faster in a very diverse population compared to one that is genetically homogeneous.

 

Is the dingo a dog at all and does it have domestic ancestry? 

 

A question which has to be investigated before is if it is true at all that the dingo has a domestic ancestry and if it is a dog at all. That question is relevant as there are some sources questioning the status of the dingo as a dog and prefer to regard it as a separate wild canid species that was never domesticated like coyotes and golden jackals. 

This idea, however, seems to be contradicted by the genetic evidence. Jackson et al. 2019 have reviewed several phylogenies based on genetic analyses and all of them have the dingo placed within the phylogenetic tree of the dog [1]. This strongly implies that the ancestors of the dingo were domestic dogs. One recent study from 2022 had the dingo as a sister group to all other dog breeds examined, but the number of dog breeds used was only six [2], therefore very low considering that there are hundreds of dog breeds. It was found that the dingo has only one copy of the AMY2B gene, which is multiplied in other dog breeds as an adaption to starch-rich diet [2]. That is, however, not an argument in favour of the idea that the dingo is a never domesticated wild canid, it just means that the duplication of the gene did not occur right at the beginning of dog domestication so that there are breeds that do not have it. That would be like claiming Sayaguesa cannot be domestic because it has the E⁺ allele, which is wildtype. The dog breeds that group with the dingo are, among others, the Chow Chow, the Akita, the Basenji and Indonesian and various Southeast Asian dogs [1,3]. Half of the dingoes tested in one study have the A29 mitochondrial haplotype (which is considered ancestral to all the other mitochondrial dingo haplotypes), which is also found in East Asian, Southeast Asian and American dogs as well as the New Guinea singing dog [4]. So from a genetic perspective, there can be no question that the dingo is a dog and shares domestic ancestors with other dogs. 

It is also morphological evidence that contradicts the idea that the dingo is a distinct, never domesticated wild canid species. Dingoes do have vestiges of domestication, including typically domestic traits such as a brain volume reduced by 30% compared to the grey wolf [5], reduced mimics and less social differentiation compared to the grey wolf [5,6], curly tails in some individuals [7] and cranial paedomorphy [8] and the males are able to reproduce all the year round [7]. Moreover, some dingoes have clearly domestic coat colour variants, such as brindle or white-spotted or piebald patterns. All these traits strongly suggest that the dingo is a dog, sharing domestic ancestors with other dog breeds. 

Also the behaviour of the dingo demonstrates that it is a dog – dingoes are sometimes kept as pet dogs, and already the Australian aboriginal people kept dingoes [9]. Alfred Brehm in Brehm’s Tierleben reported that there were dingoes kept as pet dogs and were used to protect livestock. Also, ethologist Eberhart Trumler studied dingoes kept as pet dogs and reported that they can even be made house-trained. Keeping a wild canine, be it a wolf, a coyote or jackal, as a pet dog this way would be impossible. 

Therefore, putting everything together, I think there is no reason to not assume that the dingo is a dog and shares domestic ancestors with other dog breeds. 

 

Does the dingo fit the definition of post-domestic? Is it wild or feral? 

 

My definition of post-domestic can be seen above, it has three key points. Without question the dingo is adapted to its Australian environment, it can make use of various food sources and it is adapted to the climate as the wide geographic range on the continent demonstrates. Concerning its morphology, the dingo seems to be uniform like a wild animal. Concerning its colours, they are more variable than what is commonly expected. A 2021 study found that because of the variation in the dingo’s coat colour, this parameter cannot be used to discern pure dingoes from hybrids with other, later arrived feral dogs [10]. Wild animals are usually – usually, not always – comparably uniform in colour across the species and the dingo coat colour variation is obviously a vestige of domestication. However, if the domestic coat colour variants found in the dingo (I consider all of the colours found in the dingo domestic, i.e. they arose after domestication, as none of them are the wildtype colours shared by wolves, the ancestors of dogs) turn out to be adaptive in the new environment they have been introduced to (Australia), they cannot be used as an argument against a possible wild status. If a novel trait that arose during domestication is adaptive in a new environment and becomes fixed, it would actually be in line with my dedomestication hypothesis. I never proposed that a feral domestic animal would fully revert to the original wildtype under natural selection, because some novel traits can be adaptive especially when the population lives in a new environment that is different from that of the original wildtype. In Australia, the colour of the dingo is likely better camouflage than that of the wolf in Asia where the dog was domesticated. Therefore, the colour of the dingo is likely adaptive. Perhaps some more millennia of dedomestication will eventually lead to a uniform colour, via stabilizing selection and genetic drift. Therefore, if a possible post-domestic animal has retained novel traits that arose during domestication, it still can fit the criteria for being a post-domestic wild animal as long as these novel traits are either adaptive or evolutionary neutral. But the dingo also has other remnant traits of its domestic ancestry as outlined above, some of which are part of the universal “domestication syndrome” and possibly maladaptive, including the reduced brain volume, cranial paedomorphy and curly tails in some individuals. Also, the fact that dingo males are able to reproduce all year round shows that they have not yet fully redeveloped a seasonal reproduction circle. Moreover, the fact that dingoes can be used and trained as pet dogs shows that the neurologic-endocrinologic modifications that turned dogs into domestic animals are still present in the dingo, and that it has not yet lost the potential to develop domestic behaviour. To me, this suggests that the dingo should not be considered a post-domestic wild animal. 

It is problematic, however, to draw a distinctive line between feral and post-domestic wild. Rather it should be regarded as a continuum, as a spectrum. The dingo definitely is on this spectrum, but in my opinion still closer to feral than to post-domestic wild. Interestingly, there also seems to be a continuum from other basal dogs to the dingo, as Southeast Asian pariah dogs, Borneo dogs, the Korean Jindu and the American Carolina dog are phenotypically very similar to dingoes. All of them, including the dingo, can be kept as pets. 

 

An upcoming post is going to focus on the European mufflon as a post-domestic wild animal candidate.

 

Literature

 

[1] Jackson et al.: The Dogma of Dingoes – Taxonomic status of the dingo: A reply to Smith et al.. 2019.

[2] Field et al.: The Australian dingo is an early offshoot of modern breed dogs. 2022.

[3] Larson et al.: Rethinking dog domestication by integrating genetics, archeology, and biogeography. 2012. 

[4] Savolainen et al.: A detailed picture of the origin of the Australian dingo, obtained from the study of mitochondrial DNA. 2004. 

[5] Hemmer: Domestikation, Verarmung der Merkwelt. 1983 

[6] Trumler: Ein Hund wird geboren: der Ratgeber für den Hundefreund. 1982. 

[7] Zimen: Der Hund – Abstammung – Verhalten – Mensch und Hund. 1988. 

[8] Smith et al.: Brain size/body weight in the dingo (Canis dingo): comparisons with domestic and wild canids. 2017. 

[9] Roland Breckwoldt: The dingo: still a very elegant animal. In: A symposium on the dingo. 2001. 

[10] Cairns et al.: Pelage variation in dingoes across southeastern Australia: implications for conservation and management. 2021.