A sneak peek into my book

Today I want to give you a little sneak peek into my book so that you can see what you can expect from my book "Breeding-back wild beasts: aurochs, wild horse and quagga". Now available on Amazon. 

Life reconstructions, anatomical drawings of all types of aurochs 

 

Lots and lots of photos of "breeding-back" cattle, including brand new previously unreleased photos of the Hortobagyi animals

Previously unpublished reconstructions of wild horses

Reconstructions showing the variation within the quagga

The cover; I'll reveal the bull on the cover in an upcoming post

How to rescue Bos taurus taxonomically

I once did a post on why I use Bos primigenius for the species of aurochs and cattle although it is predated by Bos taurus. Opinion 2027 of the ICZN allows this, and it has the advantage that Bos primigenius has a holotype, the incomplete Haßleben skeleton, while Bos taurus neither has a holotype nor a lectotype. However, I am not completely satisfied with that solution, because the fact that it is up to the author’s preference can create a lot of confusion. Apart from that, Bos taurus is the first name under which the aurochs was taxonomically classified (Linnaeus mentions it explicitly as “ferus Urus” in his description), so it should not end up on the taxonomical graveyard and it is questionable if opinion 2027 actually applied because the aurochs was included in the description. But how to clear up the mess and create a clear situation on what name to use for the species?

 

I see two options:

- The ICZN publishes a regulation for handling wildtypes and domesticates as different species. In this case, domestic cattle would be Bos taurus and Bos indicus, and the aurochs Bos primigenius.

- Someone does a proper redescription of Bos taurus, with a lectotype that is a “ferus Urus”, an aurochs and a few paratypes to account for the variability within the species, wild and domestic.

 

The upper option would not be useful. A universal species definition does not exist, and good arguments can both be made for the stance that domesticates are the same species as their wildtype and for the stance that they are different species. But the case of cattle shows that the latter is not practicable. Since taurine and indicine cattle descended from different variants of aurochs, they cannot form one species together that excludes the aurochs. In this case, all three (aurochs, taurine and indicine cattle) would have to be classified as separate species. Sanga cattle, which are hybrids of taurine and indicine cattle, would then be species hybrids. Hybrids between two species that only have minor differences and would without doubt be classified as one species if one did not know their evolutionary history. So the first option would be somewhat absurd.

The second option is what I would opt for. Linnaeus’ description of Bos taurus as much as Bojanus’ description of Bos primigenius are both rather minimalistic by modern standards, so a clear description that accounts for all the autapomorphies of the species of aurochs and cattle that sets them apart from other Bovini would be useful. As a lectotype (which is the type specimen assigned to a species based on a written description alone) I would use the rather complete skeleton from Neumark-Nord, which is mounted an impressive attacking pose (this one). It is very well-preserved, a typical aurochs and there is no chance that it is intermixed with domestic cattle as it is roughly 200.000 years old. I would also chose a few other specimen as paratypes, namely the Sassenberg cow (to account for the differences between male and female) and the Prejlerup bull (to cover the wide range of horn sizes within the species) and perhaps a few others.

 

The species of aurochs and cattle would then have to be labelled as Bos taurus. I think this name is just as beautiful as B. primigenius, as it just means “cattle” and it would include the wildtype which we call “aurochs”. On a subspecies level it would get a bit more complicated. If you regard domesticates as taxa (which doesn’t necessarily have to be, you could also just see them as populations that have experienced artificial selection), taurine cattle would be Bos taurus taurus and indicine cattle Bos taurus indicus, the aurochs would be Bos taurus primigenius. This would raise the question if the wild mainland aurochs needs to be subdivided into different subspecies. The latest research makes the approach of having several mainland aurochs subspecies questionable at least. I think “morphes” or “stages” might be more practicable. I go over this in my upcoming book, so please stay tuned.

 

Why I think purity makes no sense in "breeding-back"

Readers of my blog will know that I am not afraid of proposing mixing “breeding-back” cattle with less-derived zebu breeds and even different species such as the wild yak and the banteng. Some might object that this would undermine the “purity” of those cattle as domesticated Bos primigenius primigenius. This is, however, not a concern to me, for a number of reasons that I want to outline with this post. 

1. Hybridization/introgression is common in evolution 

With our increase in genetic knowledge, we have more and more cases of closely related species that experienced more or less intense introgression from each other through hybridization. I have the impression that introgression was found everywhere it was looked for, including our own genus Homo. So we can assume hybridization is a quite common factor in the evolution of species. Bovines are no exception to this, including the aurochs, where hybridization between bison and aurochs has been found in both directions (albeit the gene flow was comparably small), and I would not be surprised at all if gene flow was also detected between aurochs and banteng and between wild yak and aurochs.

2. Domestic cattle are already highly mixed between the different lineages of Bos primigenius 

The initial domestication events, as far as current knowledge goes there were two of them, concerned B. p. primigenius and B. p. namadicus. However, the resulting domestic lineages did not remain pure domestic descendants of those respective two subspecies, as there not only was introgression between them, from taurine to indicine and vice versa, but also introgression from other aurochs subspecies. The mitochondrial haplotype R was likely inherited from the African aurochs, and recently Hereford has been found to have traces of introgression from B. p. suxianensisfrom Mongolia. This introgression was probably not limited to this one breed, it just was detected there. Therefore, taurine cattle are a mix of all four mainland aurochs subspecies, and zebus possibly too, as they experienced gene flow from taurine cattle, especially in recent decades. Therefore, the remaining aurochs alleles from the four mainland subspecies are not found in four distinct domesticated lines, but are most likely all over the place in taurine and indicine cattle. 

3. Zebus share alleles with the European aurochs that taurine cattle do not have 

When the full genome of a Neolithic aurochs bull from Britain was resolved by Orlando 2015, it was found that zebus actually share some alleles with the European aurochs that taurine cattle do not have. Less-derived zebus also are more aurochs-like on some aspects than most taurine cattle, such as the trunk length and leg length, udder size and overall slenderness. Whether there is a connection between those alleles shared with the European aurochs and these phenotypic traits has not yet been investigated, those alleles could be responsible for any biological aspect of the organism. Therefore, if one wants to come as close as possible to the European aurochs, including less-derived zebus into the breeding would be wise, even if it sounds counterintuitive at first because they descend from a different aurochs subspecies. 

4. Some wild bovines might share alleles with the aurochs that domestic cattle do not have 

Just as zebus share alleles with the European aurochs that taurine cattle do not have, it is possible that living wild bovines might have some wildtype alleles found in the aurochs that cattle have lost. This might particularly be true of alleles for morphological traits that are likely homologous, such as the primigenius spiral (found in the wild yak) or a well-marked sexual dichromatism (found in the Java banteng). Thus, including these wild bovines into the breeding might be very beneficial to “breeding-back”. Species purity in the “breeding-back” results is not really a concern to me as long as the introgression is limited to genes for desired key traits, because taurine cattle are not “pure” European aurochs anyway but rather a composite of an unknown portion of mutated alleles and remaining wildtype alleles. The same goes for zebus in respect to the Indian aurochs. 

 

Thus, I would not be afraid of mixing lineages in “breeding-back”. Taurine cattle are already highly mixed, and they lack some traits and alleles that can only be effectively reintroduced by mixing lineages and selecting wisely. Note that I am not opting for rampant crossbreeding and hybridization, but rather to use small doses of introgression accompanied by targeted selection in order to keep the desired traits from each lineage and eliminate distinctive traits of the other lineage. This goes for morphological as much as behavioural, ecological and – to the degree that it is detectable – genetic traits. This way, aurochs-like bovines that blow our minds could be achieved, while that is very difficult using taurine cattle only. 

 

 

Why Equus ferus should not be used for the wild horse

The use of the binominal name Equus ferus for the wild horse is extremely common, and I used it myself in the past. However, this binomen is problematic and should not be used except in a list of synonyms of Equus caballus. 

My readers will know that I prefer to use Bos primigenius for the aurochs, thus the later-published binomen that is frequently used for the wildtype, while I treat the species of the horse (including the wild horse and its domesticated derivatives) under the name Equus caballus, which is usually used to refer to the domestic form only. This may seem inconsistent at first, but examining the problem at a deeper taxonomical level shows that it actually is not. 

I prefer Bos primigenius because this binomen has a holotype that is undoubtedly a wild specimen, the Haßleben aurochs skeleton, while Bos taurus lacks a holotype or lectotype. Type specimen are important because they clarify which species is referred to by the name. Which species is Bos primigenius? The species that the Haßleben skeleton belonged to, whatever a species definition you work with, no matter how narrow or wide your species definition is. Thus, the lack of a type specimen is problematic because it makes the situation far more ambiguous. 

As for the horse, neither Equus caballus nor Equus ferus have a type specimen. For Equus caballus, this is less problematic because it referred to domestic horses, while for Equus ferus it is a big problem because of synonymity. If two binominal names are synonymous, i.e. they refer to the same species, the rule of priority of the ICZN dictates that the name that was published first is the one to be used (the senior synonym), while the younger one is the junior synonym (as a side note, synonymity does not make the junior synonym invalid [as long as it is described accordingly to the rules of the ICZN], as it is often believed, it just means that it does not have priority and shall not be used). In the case of domestic animals, where the binomen that was erected for the wildtype exclusively often is the junior synonym, opinion 2027 of the ICZN allowed the use of the names for the wildtypes for the entire species. This includes Bos primigenius, but also Equus ferus. The ICZN explicitly assumed in opinion 2027 that Equus ferus is based on the ancestor of domestic horses, which they call “tarpan” in their document. For Bos primigenius, there is no problem following opinion 2027 because it is based on a specimen that was indeed a member of the wildtype of cattle, for Equus ferus there is indeed a problem. In order to see if Equus ferus is justifiable as the binomen of the wild progenitor of the domestic horse, we have to look at the original description of this name. 

I used Equus ferus in the past because, like everyone else, I did not check the original source and assumed that everything is alright with that name. This is the reason why it is that widely used as the name for the wild horse. For some reason, I assumed Equus ferus was based on fossil or subfossil remains of definite wild horses in Europe. When I checked the original source, I realized that this name should not be used for the wild horse. 

Equus ferus is introduced by Pieter Boddaert in his 1785 work Elenchus animalum. Boddaert gives a short description mentioning long ears, a short curly mane, a blackish grey mouse-coloured body and a short tail, and refers to the written description of alleged wild horses encountered by S. G. Gmelin in Voronezh in 1769. That is the original description of Equus ferus. The big problem is that it is far from clear what those horses spotted by Gmelin were. Whether the horses were wild, feral or hybrids of wild and feral horses. The description fits what other writers reported of free-roaming horses at that time and region. At least one member of the herd was a black domestic mare, as reported by Gmelin himself. It is generally unclear what the horses of that time and region were, and there never was a consensus among authors, be it contemporaneous ones or after the extinction of those populations in the 19^thcentury to this day. And in the lack of a type specimen, be it a holotype or a lectotype, it cannot be ascertained anymore. This case shows why type specimen are important. 

Therefore, there is no certainty that Equus ferus is based on a wild representative of the species that includes the domestic horse. If domestic animals and their wildtypes are regarded as separate species, the name to be used for the species of the wild horse would be Equus przewalskii because this binomen was the first one to be erected based on an undoubtedly wild specimen of the species. It has both a holotype and paratype which were wild Przewalski’s horses. I usually treat wild and domestic animals as members of the same species, and the first name erected for this species is undoubtedly Equus caballus by Linnaeus 1758. Linnaeus also erected a senior synonym for Bos primigenius, namely Bos taurus. However, in this case I prefer to follow opinion 2027 because the junior synonym conserved is based on a type specimen that was undoubtedly wild, while Equus ferus is based on a description which itself is based on a description of an encounter with horses of unknown status. Therefore, following opinion 2027 in the case of Equus ferus is not useful. For the same reason Equus ferus should not be used on subspecies level for the subspecies that was ancestral to the domestic horse. There is not the slightest bit of scientific evidence that the horses encountered by Gmelin in 1769 were members of the form that was domesticated 5000 years ago. For the same reason Equus ferus should not be used for Pleistocene wild horses. It should not be used for wild horses at all. If one wants to use Equus ferus solely to refer to the horses historically called “tarpan”, it is questionable if these populations deserve a subspecies status as it is unclear what those horses were. So neither Equus ferus nor Equus ferus ferus are taxonomically justified. 

This of course leaves the question what the subspecies that was the predecessor of the domestic horse should be called then. For this question to be answered, a rigorous assessment of the Holocene wild horse material that has been found in Eastern Europe would be necessary. It is well possible that someone already erected a taxon based on that material that would have priority. Whether or not a Pleistocene wild horse name (and there are a lot of those) is applicable to this form remains to be seen, this would have to be morphologically and genetically evaluated. When a subspecies is not yet scientifically described, it is referred to as species X ssp., in the case of the wild horse that was ancestral to the domestic horse it would be Equus caballus ssp. – a possible way to “rescue” Equus ferus is to assign undoubted Holocene European wild horse material to Equus ferus as a lectotype. As long as this has not been done formally, Equus ferus should not be used as the binominal name of the wild horse. 

 

Should we allow paraphyletic genera?

This post is a rather theoretic one, and some might wonder what it has to do with the main topics of my blog. However, the question if we should allow paraphyly in some cases in taxonomy is relevant for the naming of species, some of which are in the focus of this blog. 

For those who are not familiar with the term “paraphyletic”, it describes when a group is not a natural group in the phylogenetic sense, a group that has a common ancestor but does not include all descendants of this common ancestor. Paraphyletic groups are avoided in modern taxonomy because treating them as if they were the same as mono- or holophyletic groups (such that have a common ancestor and include all of its descendants) is comparing apples to bananas. To illustrate that, I take my favourite vertebrate group as an example: dinosaurs (I am actually quite a big fan of Mesozoic paleontology ever since I was a kid). It is nowadays very well-established that birds descend from non-avian dinosaurs, so that they are part of the Dinosauria clade. Why? Because Velociraptor is closer to birds than Tyrannosaurus, and Tyrannosaurus is closer to birds than a Triceratops. If birds weren’t dinosaurs, Velociraptor isn’t a dinosaur either. But in this case, Tyrannosaurus would not be a dinosaur either, because it is closer to birds and Velociraptor than to Triceratops. And so on. Consequently, birds are dinosaurs because they are nested on the dinosaur branch of the phylogentic tree. Dinosaurs themselves are part of what has traditionally been called reptiles. That means that birds should be reptiles, because birds are dinosaurs. That sounds crazy when comparing a lizard with a duck, but that’s evolution. A crocodile is closer to birds than it is to lizards, and a Tyrannosaurus is closer to birds than a crocodile. Thus, the group of reptiles in the classical sense is not a natural group because there is that decision to regard some members of this clade not as members of this group for historical reasons that go back to the time of Linnaeus. This is called paraphyly. Therefore, Reptilia is not the same as Aves (an impression that can be created by the traditional rank system of four tetrapod “classes”), rather there is the Sauropsida clade, that includes a common ancestor and all its descendants, living and extinct. On this clade, there is the Aves clade, which includes all birds. Reptilia, however, is not a clade. It is a collective term for all sauropsids that are not birds, including not very bird-like animals such as lizards, and extremely bird-like animals such as Velociraptor mongoliensis. Since paraphyletic groups make the taxonomical system much more arbitrary than it already is, they are discarded in the modern (phylogenetic) systematics, otherwise one would compare apples and bananas. Systema naturae came 101 years before Darwin’s On the Origin of species and our knowledge of extinct organisms. 

Another problematic reminiscence of the original taxonomy that came before our knowledge of evolution are “ranks” for clades. That is the hierarchical system of species, genus, family, order, class and so forth. Nobody was ever able to define these ranks objectively and universally – how can we know that Hominidae, Tyrannosauridae and Canidae are of the same “rank”? There is no definition. Aves, for example, is considered one of four tetrapod “classes”, descending from reptiles, which were considered a “class” themselves. Now we know that Reptilia is not a natural group and most researchers use the name Sauropsida instead, but Sauropsida and Aves cannot both have the same “rank” as Sauropsida is a much more inclusive group. The same problem exists with any rank. For example, the Raphidae (dodos and its close relative Pezophaps solitaria) was downgraded to a subfamiliy (Raphinae) because it is obviously nested within the Columbidae (pigeons), so both cannot be the same “rank”. Therefore, “ranks” make taxonomy even more arbitrary and only worked back in Linnaeus’ time when we had no knowledge of evolution and extinct animals (as a side note, I wonder if Linnaeus would have questioned his own system if he would have had the possibility to classify living Velociraptor or Brachiosaurus, which are obviously between the “classes” of reptiles and birds in his understanding). “Ranks” for clades are not considered to be of any factual relevance in modern systematics anymore. 

This brings us to genera, which are ranks as well. However, genera cannot simply be ignored as they are perpetuated by the binominal nomenclature in biology. Each name for a species is composed of a genus epitheton and a species epitheton. Some species share the genus epitheton because they are considered members of the same “genus” (for example Panthera leo and Panthera tigris). A genus is based on a type species, and all the other species are assigned to that “genus” when they are considered “similar enough” to the type species to be considered members of the same “genus”. The problem is, however, nobody ever defined how to measure this similarity objectively and universally and how much of that measured similarity is “similar enough”. At least not that I am aware of. But we would need something like that in order to create a consistent concept of a “genus” that is necessary because it is relevant for the naming of species. The perception of what is “similar enough” also shifts with time. Back in the 18^th century, a “genus” was about as inclusive as is a “family” is nowadays – at least in some cases (take elephants: back in the 18^th century, there was Elephas maximus, Elephas africanus and Elephas primigenius, which are nowadays considered three different genera, Elephas, Loxodonta, Mammuthus). If that was not problematic enough, there is the evolutional process going on. Species evolve into new species, the phylogenetic tree continues to grow. And as a consequence, there is inevitably the case that one genus evolves into another. On the cladogram, the resulting “genus” is paraphyletic. For example, the Haast’s eagle Harpagornis moorei is nested within the “genus” Hieraaetus, the two Bison species nest within the “genus” Bos. But saying “that genus is paraphyletic” may be not entirely correct, as a “genus” is not a clade but a “rank” that is often congruent with a given clade. A genus is defined as all species that are “similar enough” to the type species and the type species itself. Nobody defined a “genus” as a clade, so it cannot actually be paraphyletic. So, is Harpagornis moorei “similar enough” to the type species of Hieraaetus, H. pennatus? Are Bison bonasus and Bison bison similar enough to the type species of Bos, B. taurus/primigenius to be considered members of that genus? The answer is entirely subjective, and there is no way to objectively and consistently measure “similar enough”. Perhaps Harpagornis moorei is more distinct from Hieraaetus pennatus than Bison bison is from Bosprimigenius. Including Harpagornis moorei into Hieraaetus means that also a hypothetical descendant of H. mooreiwould have to be included into Hieraaetus because it nests on this clade. That means that till the end of all days all species that would have evolved from Harpagornis or another member of the Hieraaetus clade, however distinct from the Hieraaetus type species they may be, have to be included into the “genus” Hieraaetus to avoid paraphyly. And considering that each genus descends from another genus, right down to the last common ancestor of all organisms classified under the rules of the ICZN, all animals are necessarily members of the same, ancestral “genus”, if a paraphyletic “genus” is to be avoided. That means that all genera are essentially synonymous. This makes the concept of a genus meaningless, if we are consistent with the approach that a “genus” should never be paraphyletic. But a “genus” is a rank and not a clade, and ranks are based on arbitrary subjective decisions based on similarity to a defined type species, and not on clades. They are often congruent with clades, yes. And regardless of how we name the species, Bison bison is a member of the Bos clade, and Harpagornis moorei is a member of the Hieraaetus clade (by the way, the same problem also goes for species. There is no definition of a species that works universally, but if we look at the individual level, all species in the history of evolution are paraphyletic on a cladogram, because some individuals assigned to the ancestral species will necessarily closer to the new species than to the earliest member of the ancestral species. Looking at the time scale, the concept of a species is artificial and arbitrary, and species are definitely not clades). Another way to avoid genus paraphyly instead of lumping is splitting. For example, Loxodontaafricana and Loxodonta cyclotis are “similar enough” to be considered a member of the same “genus”. But it turned out in recent genetic research that L. cyclotis is actually closer to Palaeoloxodon than to L. africana. How to avoid the paraphyly? If L. cyclotis is not “similar enough” to Palaeoloxodon, it might be assigned to its own “genus” because it is closer to Palaeoloxodon, but not similar enough to be a Palaeoloxodon species. That might work when looking only at Loxodonta and Palaeoloxodon. But all genera evolved from another genus. There will always be species that are closer to the descending genus than to the type species of a given genus. As a consequence, each species would end up with its own genus, making the concept of a genus moot. So, both approaches to avoid genus paraphyly, both lumping and splitting, would, when applied consistently to all organisms, make the genus as a rank useless – the problem is more fundamental, because a rank is treated as a clade here. 

So, considering that the concept of a “genus” as a rank is arbitrary and subjective, and the concept of a “genus” as a clade makes the term absurd because all living organisms would either be members of the same ancestral genus or each species would be its own genus so that no genus is paraphyletic, what should we do? At the moment, the way it is, it is inconsistent. See the example with Harpagornis. The concept of a genus, however, is tied to the binominal nomenclature. If we change the binominal nomenclature, we will have to change the names of millions of organisms. And naming a species with two words is more definite than just one word. But we could do something intermediate: erecting a new first epitheton for each species that is not a type species of an already existing “genus”. That would also be a lot of work, but it would be more consistent and compatible with the evolution of species and the cladistic system. In some cases it would work easily, when the species epitheton is a latin name on its own. Take Panthera as an example. I was unable to find out what the type species of Panthera is, but it would work in all five species: Parduspardus, Leo leo, Tigris tigris, Onca onca, Uncia uncia. Taking the Bos clade, it would work as well, because a number of synonynomous genera or subgenera have been erected or some species epitheta are just a latinized version of the name of the species: Bos primigenius, Gaurus gaurus (gaur), Bibos javanicus (banteng), Novibos sauveli (kouprey), Poephagus mutus (yak), Bonasus bonasus (wisent, bonasus is just another name for bison, by the way) and Bison bison(American bison). For a lot of species, new first epitheta would have to be erected, especially for fossil taxa. That would be a lot of paperwork, but let us be honest, each scientist dreams of naming a new taxon, so that “Name, Year” will be mentioned next to the name forever. So, I think that many would not mind and take that opportunity to immortalize their own name by naming a new taxonomical name. And since it is not the description of a new genus that includes several species and has to be differentiated from other genera, no profound diagnosis is necessary because the species it refers to already has been diagnosed. 

I know that this is a radical approach, and it would take decades until it is established and the rules of the ICZN would have to be changed. But it would be consistent, less arbitrary, and compatible with evolution. As already mentioned, Linneaus came 101 years before Darwin, and taxonomy has already reacted by discarding paraphyletic groups. Maybe the next little revolution that is necessary to transfer taxonomy into the 21^st century is to abandon the concept of a genus. The alternative is, if taxonomy is supposed to be consistent, to allow “paraphyletic” genera (which are not really paraphyletic since they are not clades). 

 

Bos primigenius or Bos taurus?

There is some confusion about which name is the proper scientific name for the aurochs, Bos primigenius or Bos taurus. In this post, I am going to investigate the question which of those names is the legitimate scientific name for the aurochs. 

If one considers domestic cattle and aurochs different species because the former has been domesticated, the case is clear which scientific names they should have: the aurochs would be Bos primigenius, described by Bojanus in 1827, and domestic taurine cattle would be Bos taurus, described by Linnaeus in 1758. But there is no scientific consensus on whether domestic animals and their wildtypes should be regarded as one species or separate species. I tend to not regard domestic animals as taxa that need a proper scientific name at all (go here for my post on that). 

So, if aurochs and domestic cattle would be one species, with the aurochs being the wildtype and domestic cattle man-made modified versions of the aurochs created by artificial selection, what is the proper scientific name for that species? This is now where it becomes tricky. 

Due to the rule of priority of the ICZN, the first name used to describe a species has priority. In this case, Bos taurus would be the proper scientific name of the species containing aurochs and domestic cattle because it is the earlier name. However, in 2003 the ICZN decided that 17 names of wildtypes that are pre-dated by names for domestic forms should be conserved, including Bos primigenius (opinion 2027). However, to complicate the issue, Linnaeus actually referred to the aurochs in his description of Bos taurus from 1758. He mentioned the aurochs as “ferus urus” (= “wild aurochs”) living in Poland. Apparently, he was not aware of the fact that the aurochs probably already had died out when he described the species (go here for the youngest aurochs remains currently known). This is taxonomically not relevant however, Linnaeus definitely described the aurochs and domestic cattle as one species in 1758. 

Referring to the aurochs as Bos taurus is therefore definitely legitimate. However, I prefer to follow opinion 2027, also because Bos primigenius at least has a holotype (the Haßleben specimen), while Bos taurus does not. Therefore, it is up to ones’ preference whether to use Bos primigenius or Bos taurus for the species that contains the aurochs, and also depending on your opinion on the taxonomic status of domestic animals in general.

 

Taxonomy: how to classify domestic animals?

Back in the time of Linnaeus when modern taxonomy was started in 1758, some domestic animals were classified as the members of the species they were derived from, others as distinct species. Taxonomists have been trying to find a universal standard to handle the naming of domestic animals. The main question is: should they be regarded as members of the species they were derived from, or as distinct species? 

Till today, there is no consensus on how to answer this question. Both sides have good arguments for domestic animals either being subspecies of the wild species they derived from or being distinct species. 

 

Arguments for domestic animals being distinct species 

 

Domestic animals have undergone a unique evolutionary path because their evolution is mainly controlled by selective pressures determined by another species, Homo sapiens. Domestic animals have, in contrast to their wild counterparts, experienced a kind of coevolution with humans, and the abiotic and biotic factors of the “natural” (not human-influenced) ecosystem played either only a minor role in the evolution of domestic animals or absolutely none. This is a drastic difference between wild and domestic. Therefore, evolutionary, wild and domestic animals are radically different because the evolution of wild animals is not controlled (influenced, in some cases certainly, but not totally controlled) by humans while that of domestic animals is to a very large extent.

Also, domestic animals differ from their wild counterparts in structure of the genome. The absence of natural selection, the artificial selection executed by humans as well as inbreeding usually leads to a mutation accumulation (often of deleterious alleles) and decrease of genetic diversity, what is called the “costs of domestication”. Thus, domestic animals also differ genetically from their wildtypes. 

Morphologically, domestic animals are distinct from their wild ancestors, albeit the degree differs from breed to breed. For example, a Chihuahua differs from a wolf much more dramatically than a German shepherd dog. But general morphological differences between wildtype and domestic are found in any domestic form. In most cases, the difference in morphology between wild and domestic exceed the differences found between wild subspecies of a wild species. 

One of the most obvious differences between wild and domestic animals is in the behaviour towards humans. These differences are caused by modifications of the endocrinology and neurology, which probably also cause many of the morphological differences between wild and domestic (for details, see the Dedomestication series). 

Due to the absence of natural selection and the more or less intense artificial selection, domestic animals also differ from their wildtypes in physiological aspects. These aspects are directly related to the evolutionary fitness of the animals. I outlined the physiological differences between wild and domestic yaks in this post. A similar reduction of physiological fitness is to be expected in other domestic animals. 

 

Therefore, there are drastic differences between wild and domestic in their evolutionary history and presence, genetics, morphology and physiology. These differences definitely exceed the degree of variation found in wild species that have not been domesticated. Therefore, a status of domestic animals as a distinct species would be justified from an evolutionary, genetic, morphologic and physiologic standpoint. 

 

Arguments for domestic animals being members of the species they were derived from 

 

Domestic animals and their wildtypes are usually able to interbreed without fertility barriers, i.e., they can produce fully fertile offspring. According to Mayer’s species definition, they would be one species because of that. However, Mayer’s species definition does not work universally (for example, wolves, coyotes and golden jackals would be one species because they can interbreed without fertility barriers). 

Another argument for domestic animals being members of the wild species they were derived from is that the social behaviour of domestic animals does not differ from that of their wildtype in most cases when given the chance to life under natural circumstances. 

Also ecologically, most domestic animals are much like their ancestors in habitat preference, food choice and ecologic niche when living under natural circumstances. 

 

It appears that there are good arguments for both sides. It simply is the case that domestic animals are very different from their wildtype on some aspects, and very similar on other aspects. Because of that, I do not think that there will ever be a consensus on how to classify domestic animals. 

Another problem is different domestic animals probably require different solutions. Domestic dogs for example, do not have the same social structure as wolves (as far as I know). Also, ecologically they are not identical. Feral dogs often live as commensals to humans, while wolves do not. So, it might be justified to classify dogs as a distinct species, while many other domesticated animals might be classified as subspecies of their ancestral wildtype. But when not finding a universal standard for all domesticated animals, taxonomy becomes even more arbitrary than it already is. Another problem is that not all domestic breeds/populations are domesticated to the same extent. The differences from the wildtype, be it genomic, ecologic, behavioural, morphologic or physiologic, might be more intense in some breeds than in others. Extreme in some cases, not extreme in others. 

 

This leads to the question if domestic animals should be regarded as taxa at all. Domestic animals are highly heterogeneous, they differ in the extent to which they are domesticated, and often experienced secondary introgression from their wildtype and even other species during their domestication, often only certain populations. In some cases, it even is questionable if all members of a domesticated form can reproduce with each other under natural circumstances due to physical barriers (such as in the case of Chihuahuas and Irish Wolfhound). Maybe it would be better to give domestic animals no taxonomic status at all, but rather regard them as inhomogeneous, artificially created populations of certain wild animals that have been domesticated to a varying extent – varying when comparing different domestic forms to each other (f.e. horses versus dogs) as much as within the domestic forms (f.e. Spanish fighting cattle versus Fleckvieh). 

 

Is "breeding-back" too much looks-based?

Originally, when the Heck brothers started their breeding experiments, their intent was merely to show what the aurochs looked like, i.e. they only cared about the animals’ looks. Nowadays, “breeding-back” aims to produce animals that are fit to ecologically fill the empty niche of the extinct aurochs. Cattle that work ecologically like aurochs are a valuable contribution to conservation and rewilding, as they represent a species once native in Europe. 

This is the modern purpose of “breeding-back”. But isn’t it too much looks-based for this purpose? Shouldn’t the breeding focus on the animals’ ecology, health, natural instincts and ability to defend themselves against predators if the cattle are supposed to survive without human help in nature? Wouldn’t existing feral cattle populations be a better substitute for the aurochs, because they proved to survive without human help? 

 

These objections against the concept of “breeding-back” occur from time to time, and I do not consider them valid. To avoid this kind of criticism, “breeding-back” projects emphasize that they do care about the cattle’s ecology. But that seems to be unheard by those who consider “breeding-back” too much looks-based. 

I think that those who criticise “breeding-back” as too superficial imagine that the desired aurochs traits are evenly distributed among the cattle world, so that aurochs-like traits desired are coincidentally found in breeds that might or might not be robust in ecological terms, and that the breed choice of “breeding-back” is based only on those optic criteria, so that the selection of breeds used might consist of breeds that have the desired optic traits but may lack the ability to survive and thrive in nature and the subsequent breeding focuses only on those optic traits, so that the robustness of the cattle would fall by the wayside while feral cattle prove to be robust and able to survive in nature. 

This, however, is a wrong assumption. In fact, optically aurochs-like cattle are always at the same time robust, hardy landraces because they are less-derived as a whole, and often live free all the year round. That means that the animals that “breeding-back” works with are hardy and robust right from the beginning. Heck cattle are a very good example for this. As mentioned above, the Heck brothers only cared about the looks of the cattle. Yet the resulting breed turned out to be healthy, hardy and robust, because the breeds it was created from were healthy, hardy and robust. Heck cattle proved to be able to survive without human help in the Oostvaardersplassen reserve. If the assumption of those considering “breeding-back” too much looks-based was correct, Heck cattle – originally only selected for looks – would not have ended up as a hardy and robust breed that is able to survive in nature. The same inevitably goes for more aurochs-like “breeding-back” cattle like Taurus cattle, because those projects also exclusively work with hardy and robust breeds. I have to admit that I do not know of a single breed that is truly aurochs-like but is susceptible to diseases, not able to cope with weather or to live free all year round and can only live on easy-digestible food provided by humans. 

It is also not true that “breeding-back” does not care about the ecologic capacity of the animals. For example, “breeding-back” cattle in Central, Northern and Eastern Europe need a thick insulating winter coat in order to cope with harsh winters. Watussi is used in some “breeding-back” projects which is a subtropical breed and not very winter-resistant, and the winter coat of Chianina is not the longest and thickest either. The breeders are aware of that and included breeds which have a thick insulating winter coat, f.e. Hungarian Grey cattle in Hungarian Taurus or Auerrind cattle. Yes, “breeding-back” focuses on a lot of optic traits, but the ecologic capacity of the animals is an additional criterion in all modern projects. 

Regarding the behaviour of the cattle, I think that many people underestimate the natural instincts of cattle. Cattle of any breed redevelop a natural shyness after a few weeks in the wild [3]. Heck cattle are known to form defensive circles around their offspring when they consider it threatened, they will defend calves and cows retreat to a shelter when giving birth, where they hide the calf during the first days of their life [1,2]. All free-roaming cattle populations show herding behaviour, this also goes for “breeding-back” cattle. No additional breeding for natural instincts is necessary, cattle still have the natural behavioural repertoire required by a life in nature. 

 

Furthermore, the assumption that feral cattle are more qualified as an aurochs substitute than “breeding-back” cattle is not really logical when the fact that many feral cattle populations descend from ordinary farm cattle is considered. For example, the exterminated population on the Ille Amsterdam which thrived in the wild for about 150 years, descended from the following breeds: Jersey, Tarentaise, Grey Alpine and Breton Black pied [4]. If just any cattle can build up and sustain feral populations in nature and redevelop wild traits, then so will “breeding-back” cattle. 

 

Another important aspect to consider is that an aurochs-like morphology also provides fitness advantages for the cattle. Small, hornless or short-horned cattle have a harder time defending themselves and their offspring from predators than large cattle with aurochs-like horns. Also, a short dewlap and a small udder mean less heat loss during winter. And as already mentioned, “breeding-back” cares about the winter coat. Wildtype colour is probably more suitable for a life in nature than a piebald colour, piebald calves are detected much easier by predators than the chestnut colour of wildtype-coloured calves. 

 

All in all, I do not think that “breeding-back” is too much looks-based and I am 100% confident that “breeding-back” cattle will fulfil the ecological niche of the aurochs very well if they were released into nature. 

 

Literature 

 

[1] Frisch, W.: Der Auerochs – das europäische Rind. 2010. 

[2] Poettinger, J.: Vergleichende Studie zur Haltung und zum Verhalten des Wisents und des Heckrinds. 2011. 

[3] Bunzel-Drüke et al.: Praxisleitfaden für Ganzjahresbeweidung in Naturschutz und Landschaftsentwicklung -  “Wilde Weiden”. 2008. 

[4] Rozzi & Lomolino: Rapid dwarfing of an insular mammal – the feral cattle of Amsterdam Island. 2017. 

 

 

 

The problem with fixing traits through conventional breeding

Today comes a rather theoretic post on the obstacles of breeding, which is relevant for “breeding-back”. One of the biggest challenges for “breeding-back” is to genetically fix the desired traits. By fixing traits I mean achieving that all the individuals of the population have the desired trait. For example, the E+ allele is fixed in Taurus cattle because all individuals are homozygous for this allele. Fixing a trait requires consequent selection and to consider the difference between genotype and phenotype. 

 

As an example: Heck cattle of the Wörth/Steinberg lineage have very large thick horns that match those of the aurochs in absolute and relative dimensions. However, their curvature does not curl inwards enough in most individuals (see this individual). Maronesa sometimes have a very narrow, aurochs-like horn curvature, but lack the desired volume (see this individual). Something intermediate would be ideal. And considering that those traits are very likely regulated by more than one gene, the results of crossing Wörth/Steinberg Heck cattle with Maronesa would likely be intermediate, and hence show the desired phenotype: horns with the right volume and right curvature. Is the work done with that? Not even nearly – the desired phenotype would have to be genetically stabilized in the individual and to be fixed in the population. Simply backcrossing the offspring with the individual with the desired phenotype again and again will not be able to do that, and here is why: 

The cross individual might have the desired phenotype, but that phenotype is the result of maximum heterozygosity between the parental breeds. It has the alleles for the horns that are not curled enough and the alleles for the narrowly curled horns on the same loci, and it has the alleles for the very large horns and the not so large horns on the same loci, resulting in a phenotype that is intermediate and hence “perfect”. When the animal produces offspring it either passes on the alleles for the very large horns, the not so large horns, the not very curved horns or the narrowly curled horns, but it will never pass on the desired phenotype because it is the result of a heterozygous state. Thus backcrossing with the F1 individual with the desired phenotype will be pointless because it is genetically unable to stabilize the phenotype. By stabilizing in this case I mean that the individual always passes on the desired phenotype to its offspring, which is the case when the alleles producing the desired phenotype are present homozygous. When the phenotype is the result of heterozygosity, stabilizing it is impossible. However, since both horn volume and perhaps (or: hopefully, for this example) horn curvature are quantitative traits that are regulated by more than one locus, there is the chance to genetically stabilize the desired phenotype. As a simplified example, let us assume that horn size is controlled by only two loci, A and B, (unlikely, but only an example) and that Wörth/Steinberg Hecks are homozygous for alleles producing very large horns on both locus A and B, and that Maronesa are homozygous for alleles producing not so large horns on A and B. Thus, they only pass on very large horns or not so large horns, it is stabilized in their genome. What we want is a stabilized intermediate phenotype by crossing those breeds. The F1 individual will have the right phenotype because it is heterozygous for both very large horn alleles and not so large horn alleles, producing the intermediary phenotype desired. But, as mentioned above, it is impossible to stabilize this phenotype with this genotype, the genotype is not right yet. The right phenotype in this individual is actually only an “illusion”. The only way to stabilize the intermediary phenotype is to produce offspring that is homozygous for alleles producing very large horns on either locus A or B, and that is homozygous for not so large horns on the other locus. This way, the intermediate (= desired) phenotype can be passed on in a stable fashion. If horn curvature is a polygenic trait too, it works the same with horn curvature. It is impossible to have that in a first-generation hybrid. Breeding this F1 individual to another breed or one of the parental breeds will not stabilize the desired phenotype, even if you backcross it with the F1 again and again and again. This is why “breeding-back” herds are still heterogeneous and not genetically stable even if the same breeding bull has been used for multiple generations. The most efficient way to stabilize the desired phenotype is to breed the F1 individual to another F1 individual of the same combination (if you have only breeds A and B, in this example Wörth/Steinberg Heck and Maronesa). This way it is possible that an individual is born that has only alleles from Heck on one locus and only alleles from Maronesa on the other locus, if the goal is to stabilize the intermediary phenotype of a quantitative trait (f.e. body size or horn size). If you have such a true F2 individual with the right genotype (the more individual of this combinations you produce the less luck you need, the less individuals the more lucky you have to get for that), it is possible to fixate the trait in the population by backcrossing its offspring with it. 

Summa summarum: If you cross two breeds because a phenotype intermediary between both breeds is the phenotype you desire, the F1 individual will not have the right genotype for stabilizing the trait in the population, no matter how long you use it as a sire. If you produce a true F2 of this combination, the offspring has at least the chance to have the right genotype. 

If you are looking at a monogenetic trait, and you want to stabilize the intermediary phenotype that is the result of a heterozygous state, you will never ever be able to stabilize the intermediary phenotype in the population. To use Wörth/Steinberg Heck cattle and Maronesa as an example again: the former have horns that often are too upright for what is average in the European aurochs, while the angle of the horns is too narrow in most Maronesa. Let’s say the parental individuals have horns of an angle of 90° (Heck, too upright) and 35° (Maronesa, too narrow angle) and you want something intermediary to produce phenotype like in the European aurochs. If horn orientation relative to the snout is a monogenetic (Mendelian) trait, and the heterozygous state produces something intermediary like 60° as in the aurochs, it is impossible to stabilize this in the population, because the F2 will either have the 90° phenotype, the 35° phenotype or the desired 60° phenotype. You may be happy about the individuals having the right phenotype, but will never be able to fixate this trait in the population using these two breeds if horn orientation was regulated only by one locus. You would have to find a breed that has the right allele, as long as the right allele was not lost during domestication. I do not think that horn orientation is a Mendelian trait, but just to illustrate what I am saying, it would be impossible to fix a desired phenotype using two parental breeds that are homozygous for a phenotype that is not the desired phenotype. 

It gets more complicated if there are more than two alleles, f.e. three: let us say we have only one locus with three alleles, allele A producing the right phenotype when homozygous (60°), allele B producing very upright horns (120°) when homozygous, and allele C producing a very narrow angle when present homozygous (20°). Now let us assume that we have two parental individuals, one with horns having a 90° orientation and a genotype A//B (intermediary between the phenotypes A//A, the desired one, and B//B, the very upright horns), and one with a horn orientation of 35° with a phenotype A//C. By crossing these two animals, which both do not have the right phenotype, you would produce the following genotypes and phenotypes: 50% would be A//A, the right phenotype of 60° and right genotype, B//C would have a phenotype intermediary between 120° and 20° so perhaps the desired 60° but the wrong genotype, A//B with 90° as in one of the parents and A//C with 35° as in the other parent. If you produce only one offspring individual, the genotype will come about by chance. Either you have an individual that has the wrong phenotype and will be discarded, or you have the right phenotype but do not know if the genotype is right (A//A) or wrong producing the same or a similar phenotype (B//C). You can only know by producing further cross generations and analysing the offspring, when it is already too late if you picked the wrong individual. Thus, either the genetic background of traits is resolved (the individual alleles and the phenotypes produced are known, which is currently only the case in colour traits), or you have to accept that you also need a lot of luck or in some cases, stabilizing the trait is impossible with the breeds chosen because it is the result of a heterozygous state in a monogenetic trait.

Summa summarum #2: In a monogenetic trait, you need to have the one right allele in order to stabilize the fix phenotype. If the allele has been lost during domestication, it is not possible to stabilize the desired phenotype. 

 

Another problem for fixing desired phenotypes is genetic linkage. It is very likely that some domestic (= undesired) alleles are genetically linked with wildtype alleles (= desired) on the same chromosome. This can be a problem for “breeding-back” in two ways. For once, it might be the case that some desired phenotypes are genetically linked with domestic phenotypes in some breeds, f.e. the right colour might be linked to a wrong horn shape or other examples. In this case, a breed would have to be found in which this is not the case or you must hope to get very lucky with recombination. Another problem could be if a number of wildtype alleles for wildtype traits that are not morphologically visible (f.e. physiological traits) are genetically linked with visible mutations such as “wrong” colour variants or deviant horn shapes, the selection for aurochs-like morphology or looks might eradicate other wildtype traits for physiology, genetic fitness or immunology. This would be a case of bad luck, but cannot be ruled out completely. 

 

This is why it is a huge pity that there is currently no project that is trying to execute “genetic breeding-back” (go here for a post on that issue). For “genetic breeding-back”, the resolved full genome of that one British aurochs bull could be used as a template in order to accumulate wildtype alleles responsible for all aspects of the organism (physiology, morphology and life appearance, immunology, development, genetic fitness etc.), and produce something that is as aurochs-like as possible with living animals (not only in morphology, but also all other organismic traits). This would require a lot of extra research that has not been done yet, and it is problematic that we only have the genome of only one aurochs, which bears the danger of selecting against other wildtype alleles not found in that one particular genome. 

 

 

 

The past 10 years in "breeding-back"

I have been researching on the aurochs, wild horse and “breeding-back” for exactly ten years now. It was in 2011, when I worked on a drawing of Europe’s large mammals that I looked at the Wikipedia page in order to get some knowledge on the aurochs’ physical appearance. I had been aware of “breeding-back” previously, but did not pay much attention to it. The photograph of the Heck bull “Ari” from the Wörth/Steinberg lineage immediately created my fascination for this subject. 

This was in a time when Heck cattle had a kind of monopoly for being an aurochs-like cattle breed, as the primitive landraces from Southern Europe were barely known outside the Iberian peninsular. But I learned of these breeds quite early because I joined the aurochs thread in the old Carnivora Forum, where a lot of photos of primitive Iberian breeds were shared. In the same year, I visited the Hellabrunn Zoo in Munich, which is where modern Heck cattle originated. The Hellabrunn Heck cattle herd is remarkable for its perfectly aurochs-like colour with a good sexual dimorphism. Being aware of the fact that Heck cattle is only one of many aurochs-like breeds, I enjoyed seeing living cattle with the colouration of an actually extinct animal very much. Thanks to the Carnivora thread, I also learned about the Tauros Project (today: Tauros Programme), which had only one crossbred individual at that time that was actually still a calf (the bull Manolo Uno). There also was barely any information on Taurus cattle on the web, with only two PDFs showing first-generation crosses at young age. I had no idea that by that time, animals like the bull Lamarck were thriving in the Lippeaue reserve. So there was Heck cattle, by many considered to be the only aurochs-like breed, Taurus cattle which were pretty much incognito back this time and the Tauros Project which only had one calf. 

I felt that the monopoly of Heck cattle was unjustified, and the Wikipedia articles in German and English were pretty “pro-Heck cattle” back this time, with little well-grounded information and unempirical claims. The Wikipedia article on the aurochs was not satisfying either, with some inaccuracies and no precise information on the aurochs’ physical appearance. And it was extremely difficult to find information and photos of the primitive Southern European breeds. So I started to rewrite the Heck cattle and aurochs articles in both the German and English Wikipedia, mainly using Cis van Vuure’s 2005 work as a reference. Also, I created Wikipedia articles for some of the primitive European aurochs-like landraces, with photos, because I thought this would be the most effective way to make the knowledge on these valuable breeds more accessible to a larger-scale audience. Also, I thought that by precisely describing the aurochs’ physical characteristics on Wikipedia that the differences between Heck cattle and the aurochs would become apparent. 

In 2013, I started the Breeding-back Blog. Back this time, there were not many people interested in the aurochs and “breeding-back” on the web. There was the Carnivora thread, which was mainly attended by four or five users on a regular basis. In the following years, the situation began to change. 

 

For once, “breeding-back” itself began to grow. The Tauros Project expanded to multiple countries and acquired quantity quite fast, and a new project, the Auerrind project came into existence. Taurus cattle finally found their way into the internet, also because – excuse my self-praise here – I went to the Lippeaue reserve several times and covered them on my blog, with many photos (now Taurus cattle also have a very good web presence on the webpage of the ABU). Also, the number of rewilding projects increased, and both practices got considerable media-coverage (compared to the years before 2011). And the number of people interested in “breeding-back” and the aurochs and also of course rewilding multiplied and multiplied. 

I see that every time I look at my blog’s statistics. My blog has a total of more than 900.000 clicks, with 200-400 clicks per day, some posts have over 1000 clicks and it has 2000 comments in sum (a big thanks to all my readers by the way!). I would have never expected this to happen, as “breeding-back” and the aurochs is a very small niche, so to say. But the number of people interested in this subject is constantly increasing. I see a lot of people who are not only interested in the aurochs, but also know a lot about this subject. They precisely know what an aurochs looked like, know all the projects and special herds/lineages in great detail. Also, the primitive aurochs-like breeds are now well-known to a lot of people. Back in 2011, all of this was not the case. 

I think that of all the animals killed off by mankind in historical times, the aurochs is perhaps the species that currently gets the most attention. The Thylacine also has a huge fan club (a fan club that also has a longer history), but I get the feeling that the “aurochs fan community” got ahead of that of the Thylacine. The mere fact that there is such a community now is worth noticing, because it did not exist back in 2011. 

 

Why did that change so dramatically? I think this has two main reasons: a) there are now more “breeding-back” projects than back then, with a lot more animals and also media-coverage b) the information on “breeding-back” and the aurochs is now easily accessible. The Wikipedia articles are pretty good (I just initiated the changes, a lot of people have helped to progress the pages since 2011), you can easily learn about the life appearance and biology of the aurochs, learn about the primitive aurochs-like breeds and learn about the “breeding-back” projects on the web. I hope that my blog contributes to that as well. 

 

The fact that people are increasingly aware of the anatomy and biology of the aurochs also has a kind of positive feedback effect on “breeding-back”. I get the impression that Heck cattle has slowly increased in quality during the last 10 years because breeders are increasingly aware of the anatomy of the aurochs. The slow process of improvement is not true for all Heck herds, but for some. Also, Heck cattle lost its monopoly on being “the” aurochs-like breed. This was necessary to seize the potential we have in modern day cattle. 

While the myth that Heck cattle are “recreated aurochs” is a thing of the past now, the acceptance of the myths concerning the European wild horse and its purported descendants has not changed yet. Still a lot of people believe the “the Konik is the Tarpan descendant” myth, the Sorraia myth and the Exmoor pony myth (go here for a review of these stories). These stories sometimes are even repeated in technical, peer-reviewed papers, which is concerning. But maybe this might change in the future, as fact-based information on these three breeds and on the European wild horse are at least available in the internet now. 

 

I think that we live in the prime time of “breeding-back” today. There are several projects, people now are aware of the anatomy of the aurochs and of suitable breeds (which was not the case, f.e., when the Heck brothers did their breeding experiments) and they have more attention than ever since there is a large number of people interested in this subject. “Breeding-back” already has produced a number of great animals, and there will be much more in the future. I am looking forward to that, and I am also looking forward to cover them on my blog as I always try to do. 

 

Is "breeding-back" necessary?

Originally, “breeding-back” as it was invented by the Heck brothers, aimed to recreate extinct species. We now know that this is not possible working with domestic descendants only, as the subject is much more complicated than just uniting visible traits found in primitive breeds. Therefore, the goal of “breeding-back” changed. Nowadays the main purpose of this method is to authentically replace the extinct wildtypes in the wild, filling the empty ecologic niche. In order to accomplish that, the set of criteria now also includes ecologic traits. The cattle (or horses, if there were “breeding-back” projects for horses) not only have to look like their extinct wildtype, but they also have to be capable of surviving in nature. Achieving that is not a big problem, was most primitive breeds already are very hardy landraces. 

But is “breeding-back” really necessary to fill the ecologic gap? 

 

For this question, the answer is pretty clear: no, it is not necessary. Releasing a couple of hardy landraces back into the wild would do the job as well, no elaborate selection on wildtype traits is actually necessary for these animals to survive in nature. While it is true that large, long-legged, athletic cattle with large horns will have a much easier time to defend themselves against predators than small, short-legged cattle without horns, natural selection will probably enforce wildtype traits anyway. Also, many landraces are already quite aurochs-like, such as Sayaguesa for example. They are large, have a comparably aurochs-like morphology and horns, and the colour is right as well (except for the very reduced sexual dichromatism). Add Maronesa genes by releasing both breeds in the same area and most aurochs fans will be satisfied. The same goes for Spanish fighting cattle (Lidia). The probability that they survive in nature and function like their extinct ancestor is very high, as there are feral cattle populations that descended from derived breeds that were not landraces (such as on the Ile Amsterdam or New Zealand). So just releasing a number of cattle from several primitive landraces and letting them breed for themselves and do their thing in natural areas will do the job sufficiently in any case. I have the suspicion that this is the plan the Tauros Programme. So far, they have done exactly that and nothing more (at least nothing that they have published). 

 

If that is the case, why doing “breeding-back” in that intensity at all? I see three main reasons: 

- to see how much similarity to the extinct wildtype can be achieved by selective breeding 

- educational purpose: by showing what an aurochs (or European wild horse) looked like and was like you educate people zoologically 

- a homogeneously wildtype-like phenotype is important for the public acceptance as a wild animal. If the cattle are heterogeneous in appearance they would look more like a bunch of escaped farm cattle, while the phenotype of the aurochs was undoubtedly that of a wild animal. There are indeed people who are against using cattle (or horses) in rewilding because they consider it animal cruelty to let domestic animals live in the wild. It is thus important for the public acceptance of the projects to communicate these are “special” animals bred to live in the wild. 

 

So from a purely ecological point of view “breeding-back” is not necessary. But having a breed of cattle that is as aurochs-like as possible certainly has some advantages. In the end, it is about authenticity. An authentic proxy for the aurochs is more satisfying for nature lovers, has a higher chance of being accepted as a wild animal in the public eye, is more educative, and probably has a higher ecologic fitness compared to randomly chosen landraces due to the selective advantages a wildtype-like phenotype likely has. It is also a matter of opinion. Surely there are more pragmatic people that do not care that much about authenticity, but there are also (perhaps more idealistic) people that do want to replace the aurochs as authentically as possible. And there is enough of the latter category that there are “breeding-back” projects, and even several of them. 

Ancient Europe's landscape: grassland savannah or forest?

There is an on-going controversy on what Europe’s original landscape, untouched by human influence, was like: either heavily forested, a grassland savannah or a mix of open forests, park-like landscapes and grassland. 
The traditional view is that of Europe being a heavily forested continent. This view has been challenged in recent decades. It has been proposed that herbivores prevent open landscapes from becoming forested by damaging forest growth with their feeding, and are even able to turn forests into open landscapes this way. As a result, Europe’s original landscape would not have been one big forest but a mix of open landscapes, park-like landscapes and forests [1]. Some even claim Europe was a large grassland savannah. 
Indeed no large mammal in Europe is dependent on forests while they need at least some open landscape in their habitat [2,3]. Africa is used as an analogue, where large herbivores are claimed to create the open landscape we are familiar with. Especially elephants, which uproot trees are suspected to create open landscapes [3]. 
There is conflicting data, however. Studies suggest that the uprooting of trees by elephants does not diminish the forest but instead speeds up the forest rejuvenation [4]. And it is overlooked that not only the savannah but also the deep rainforests are home to large herbivores, such as the forest elephant (Loxodonta cyclotis), the forest buffalo (Syncerus nanus) and the okapi (Okapia johnstoni) [4]. There are also several species of large herbivores living in the rain forests of South-East Asia (banteng, gaur, Asian elephant). If large herbivores create open landscapes, elephants in particular, the forest elephant would be a contradiction in itself: a forest-adapted elephant (f.e. the smaller size) would not exist if elephants created open landscapes with their feeding and uprooting of trees. 
Furthermore, and more importantly, palynologic data suggests that Europe was densely forested until very recent millennia when man started agriculture in Europe [4]. Also the insect fauna shows that forest-dwelling species were very common in Europe until recently [4]. It is argued, however, that also an intensely grazed grassland area has the same palynologic signature as a closed forest (see for example the works of Frans Vera). But this apparently is only the case at a very high herbivore density [4], and it cannot explain why the data from insects suggest high forestation. 
Another argument against ancient Europe being a grassland savannah and for a strongly forested continent is the distribution of the European wild horse in the Holocene. The horse is heavily dependent on a grassy diet and is an open land animal. It got very rare in Europe after the last glacial [5]. It virtually disappeared from Central Europe [5]. When agriculture began, the equine remains increased again, possibly due to an increase in open landscapes [5]. These distribution patterns contradict the hypothesis that Europe would have been a grassland savannah due to grazing and instead supports the hypothesis of Europe without human influence being a mostly forested continent. 
 
Europe’s original landscape continues to be a subject of debate. The data that is available to me suggests that the idea of ancient Europe being a grassland savannah with large herds of horses is not the likeliest scenario. 
 
Literature 
 
[1] Bunzel-Drüke et al.: Der Einfluss von Großherbivoren auf die Naturlandschaft  Mitteleuropas. 2001. 
[2] Beutler: Die Großtierfauna Europas und ihr Einfluss auf Vegetation und Landschaft. 1996.
[3] Bunzel-Drüke et al.: Überlegungen zu Wald, Mensch und Megafauna. 1994.  
[4] van Vuure: Retracing the aurochs – history, morphology and ecology of an extinct wild ox. 2005. 
[5] Sommer et al.: Holocene survival of the wild horse in Europe – a matter of open landscape? 2010.