I am writing a book on "breeding-back"

During the last 3 years, I have been writing a book on “breeding-back” and everything related to it. Basically compiling all the knowledge and literature I have been gathering on this blog over the last 10 years. The bulk of the work covers the aurochs, but also of course the wild horse and the quagga is covered as well. 

 

In this book you will find everything I covered on this blog in a structured and comprehensive manner, and also of course new information. It will feature: 

-       An overview over the impact of large herbivores on the landscape 

-       A precise description of what we know about the aurochs 

-       How domestication changed the wild bovine

-       A history and evaluation of and ideas for “breeding-back” the aurochs in as much detail as possible 

-       A precise description of what we know about the wild horses of Europe 

-       A compilation of historical evidence of the horses historically called “tarpan” 

-       A critical evaluation of the stories revolving the Konik pony, Exmoor pony and Sorraia 

-       Ideas for a “breeding-back” project focusing on horses 

-       The quagga and “breeding-back”

-       My dedomestication hypothesis

-       Thoughts on the potential de-extinction of recently vanished megafauna 

-       qualitative photos and artworks, some of which I have not published so far 

 

I hope to publish it within next year (2024).

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. 

 

 

European and Indian aurochs may have vocalized differently

Recently I learned on a Facebook group that taurine and indicine cattle vocalize differently. Previously, I had assumed that all cattle vocalize in the same way, and that that way is typical for the entire species of Bos primigenius. It turns out that there are differences between the vocalization of taurine and indicine cattle, and I suspect those differences could be inherited from their wild ancestors. 

Taurine bulls often make repetitive, trumpeting calls: 

Zebu bulls, on the other hand, omit growling grunts, resembling the roar of a jaguar: 

I find this fascinating. I consider it quite likely that both calls are inherited from the European and Indian aurochs respectively, although we cannot rule out that mutations affecting behaviour during domestication created this difference in vocalization. 

Trunk length of the aurochs and the mysterious Cambridge specimen

In Cis van Vuure’s classical Retracing the aurochs it is written that the shoulder height of the aurochs nearly equaled the trunk length, in contrast to most domestic cattle where the trunk is longer. Somehow “nearly equals” became “equals” in my memory, although I read the book several times and it also cites a source that gives precise data, namely that the height of the withers to the trunk length ratio varied 1:1,02 to 1:1,1. One has to be cautious, however, because the withers height is influenced by the length of the spinal processes in the shoulder region, which may vary from individual to individual and differs between the sexes. So calculated the ratio between the height of the upper margin of the shoulder blade and the trunk length using photos of 10 aurochs skeletons in lateral view. 

There is also a written remark of the trunk length of the aurochs by a person who visited living ones, Anton Schneeberger. He states in his letter to Conrad Gesner that the cows are “not as long” as the bulls. 

 

Specimen	Sex	Ratio of shoulder blade height to trunk length
Braunschweig	male	1:1,14
Friemersdorf	male	1:1,11
Hammerslöv	male	1:1,15
Prejlerup	male	1:1,06
Sassenberg male	male	1:1,17
Store-damme	male	1:1,17
Vig	male	1:1,11
Sassenberg female	female	1:1,03
Cambridge	? female	1:1,19
Mönchengladbach	? female	1:1,17

 

The Sassenberg cow is the only mounted specimen of the European aurochs which I am highly confident that it is from a cow, because of its entire morphology. For the Mönchengladbach and Cambridge specimen, I am not so sure. Especially the Cambridge one puzzles me. The morphology of its postcranial skeleton resembles that of unambiguously male specimen, such as the Prejlerup specimen, f.e. because of the relatively long and massive spinal processes in the shoulder region. The skull, however, looks very feminine compared to definitely male skulls such as the London one, because of its barely protruding orbital bosses and the overall gracile build. Also, the Cambridge skeleton is merely 145 cm tall, what would be 150-155 cm in life, which is suggestive of a cow, particularly from Northern Europe. 

The Sassenberg cow has the shortest trunk, barely longer than the height of the shoulder blade. This fits the historic description by Schneeberger. As it happens, the Cambridge specimen has the greatest relative trunk length. This could have various reasons: 

- The Cambridge skeleton is from an – extraordinarily small – bull  

- Trunk length is not a reliable indicator of sex in the aurochs 

- The sample size is too small to determine anything 

Actually, I consider the third reason the most likely one. Guessing by eye, it was always my impression that in domestic cattle the cows are shorter than the bulls too, but I have no reference at hand confirming this. It would be interesting to investigate this thoroughly with osteometric measurments. 

New photos of the Watussi-influenced Auerrind cattle

 Here are some new photos of Watussi-influenced Auerrind cattle: 

© Yannick Weinand

These photos show the Watussi x Chianina cow. It is interesting to see its phenotype develop, as this combination bears a huge potential for future crossbreeds.

 

All the subsequent photos are © Claus Kropp

This is the (Sayaguesa x Hungarian Grey) x (Sayaguesa x Watussi). It looks great, it has a perfect aurochs colour and a very long snout, much of the Sayaguesa-appeal. 

This cow is the Chianina x (Sayaguesa x Watussi). Her morphology is very good, and her light but not diluted colour endorses the suspicion that Chianina has some degree of sexual dichromatism masked by the dilution alleles. Also the snout is very long. 

This is one of the Maremmana x Sayaguesa cows with the Sayaguesa x Chianina bull behind it. This combination bears good potential, Chianina and Sayaguesa bring the size, Maremmana horn length and a good winter coat. 

This young bull is (Watussi x Sayaguesa) x (Watussi x Chianina). It's great that this combination exists, it has the potential for tremendous horns and the colour is right as well. 

This is the (Sayaguesa x Grey) x (Sayaguesa x Watussi) bull, a combination which I think bears great potential. The horns seem to grow huge, especially considering that the bull is not even 3 years old (!). 

I have to say that I am very happy with how the Auerrind project is progressing. Those are great animals with a lot of potential for even better future crosses.

Fascinating news: Mongolian and Iberian aurochs influenced cattle; another dwarf aurochs described

The last few months saw the publication of three very interesting papers on the aurochs. One analyzed ancient genomes of Mongolian aurochs and found that it influenced ancient Mongolian domestic cattle, an influence that lives on in a breed you would never expect. Another one analyzed bovine material from the Holocene of Spain, and found significant introgression from Iberian aurochs into cattle. The third paper describes another aurochs dwarf form or subspecies, this time from a Greek island. 

-) Mongolian aurochs influenced Mongolian cattle 

Aurochs material from Mongolia was analyzed and all of them had the mitochondrial haplotype C (which was also found in Chinese aurochs assigned to B. p. suxianensis and is distinct from the European haplotypes). It turns out that B. p. suxianensis influenced local Mongolian cattle, which is what I expected because I consider it very likely that introgression from wild to domestic occurred anywhere aurochs and cattle lived side by side. However, modern Mongolian cattle are different from ancient Mongolian cattle. In modern cattle, Mongolian aurochs influence was detected Hereford. This is rather surprising. 

In the phylogenetic analysis, haplotype C is a sister group to the western Eurasian haplotypes, forming a clade that is a sister group to haplotype R, which was found in African aurochs. The Indian haplotypes (from zebu) are an outgroup to all the other haplotypes of the species detected so far. This indicates that the European aurochs was closer to the East-Asian aurochs than to the African aurochs, and that the Indian aurochs was the result of the first cladogenesis event in Bos primigenius that we know of. 

Brunson et al.: Ancient Mongolian aurochs genomes reveal sustained introgression and managment in East Asia. 2023 (preprint) 

-) Iberian aurochs influenced western European cattle 

Archaeological material from the late Holocene of Spain was analyzed and the fully resolved British aurochs genome used as a reference for pure aurochs. It was found that some remains were up to 90% aurochs, others as low as 20% and the rest, respectively, domestic. This indicates that domestic cattle and aurochs hybridized frequently, leading to introgression to both wild and domestic populations. The data suggests that male introgression from aurochs was more common than female introgression, which is something that I expected because of the handling of cattle back in early days. They were kept free all year round, where wild bulls could have easily mated with domestic cows - a behaviour that is also historically documented (Schneeberger). It gets even more interesting: The genomes of modern western European cattle breeds are between 20 and 25% aurochs. Lidia was also tested, but did not show a higher portion of aurochs. The authors, however, speculate that the aurochs material preserved in Lidia might be key genes for behaviour and appearance, explaining the high degree of similarity between aurochs and Spanish fighting cattle. I too consider this highly likely. 

Günther et al.: The genomic legacy of Human management and sex-biased aurochs hybridization in Iberian cattle. 2023 (preprint). 

-) Bos primigenius thrinacius 

Previously to the new paper, two insular dwarf aurochs subspecies were described: B. p. siciliae on Sicily and B. p. bubaloides on Pianosa, Pleistocene of Italy. There are also remains from Malta which may constitute a third insular subspecies that has not yet been formally described. Now another one, from Kythera Island, Greece, has been described. It seems to be the smallest of the dwarf aurochs, slightly smaller than B. p. bubaloides, which had a withers height of 100-120 cm. No complete skeleton of B. p. thrinacius has been recovered, unfortunately. But what is known seems to suggest that the sexual dimorphism was reduced, and there was a tendency to loose premolar 2 in the dentals preserved. The dentals also look comparably short to me by aurochs standards. I would say this is in line with general tendencies of insular mammals to show signs of paedomorphy, similar to domestics. The study was co-authored by Roberto Rozzi, who did a lot of interesting research on insular bovids. 

Siarabi et al.: Insular aurochs (Mammalia, bovidae) from the Pleistocene of Kythera Island, Greece. Quaternary Science Reviews (2023). 

How (not) to quantify aurochs-likeness in cattle

I have been trying to quantify aurochs-likeness in extant cattle multiple times and it turned out to be very difficult. It starts with the question of what is a “trait”. For example, is coat colour a trait or is it rather a complex of many traits (what types of melanin are expressed, where they are expressed et cetera)? Some traits also interfere with each other. As an example, leg length (i.e. proportions) influences height and other parameters. If a short-legged bull is only 150 cm tall, it is shorter in height than the European aurochs. If it had the right leg length it might be 20 cm taller, meeting the height of some European aurochs. Is, considering that, both the body size of the animal and the leg length deficient, or is only the leg length deficient? Even more problematic is the thought that not all traits are regulated by the same number of genes. Colour is regulated only by a handful of genes, perhaps roughly a dozen, while the bodily morphology is much more complex and influenced by many genes (I assume so because endocrinology influences the body morphology quite dramatically, and the hormone system is influenced by a very large number of genes). So which cattle individual is more aurochs-like, i.e. closer to the aurochs, one that has the right colour but a totally domestic morphology, or one that has the right morphology but deviant colours? If every defined “trait” (what is a trait?) is assigned an equal value, both individuals would be equally aurochs-like. This neglects the fact that in one individual a lot of genes are “right” and only a handful “wrong” while in the other a lot of genes are “wrong” and only a handful “right”. Therefore, the most objective and useful way to compare the phenotypic aurochs-likeness would be to compare every single gene that has an influence on the phenotype. This is practically near impossible as mammals have between 20.000 and 30.000 genes and we do not know the phenotypic impact of every single allele on every single gene. Therefore, an attempt to quantify even the solely phenotypic similarity to the aurochs necessarily has to be somewhat simplistic. I made lists of aurochs-like traits and scored a number of cattle breeds for those traits, each time a slightly different approach and the result always was that Sayaguesa and Lidia were among the two most aurochs-like breeds, “breeding-back” results were not included. It is very difficult to score “breeding-back” results as they are not as homogeneous as traditional breeds. For example, the horn size of Heck cattle varies greatly between individuals, herds and lineages. Averaging the traits found in the “breeding-back” results each would not account for the variability found within them. What can be done is scoring single individuals of “breeding-back” breeds/populations, but that leaves a lot of room for bias. One can take the best or the worst individual, or trying to figure out which individual might be representative of what is average for the breed, but that is very difficult and would, again, not account for the variability in the populations. 

All in all, I think trying to systematically objectively quantify the aurochs-likeness of cattle can only provide a very rough impression that is not any more useful than just looking at the cattle and comparing them. 

 

How bulky was the aurochs?

As mostly only bones are preserved of the aurochs, reconstructing the soft tissue surrounding them necessarily involves speculation. The anatomy of living wild bovines and cattle provide useful clues for that. But they do not tell us how pronounced the muscles really were, how large the intestinum was (this is relevant as domestic cattle have a much larger intestinum than wild bovines) and how much tissue surrounded the bones in general. 

Looking at a skeleton, there often is the tendency to underestimate the bulk of tissue that surrounded the bones. Those who are familiar with dinosaur paleoart will know of the term “shrink-wrapped” dinosaurs. That term arose when it was recognized that most dinosaur reconstructions from the 1990s and early 2000s were too skinny, often to a degree that makes anatomically no sense (which was a result of a countertrend to making dinosaurs extremely bulky in earlier 20^th century and 19^th century reconstructions). Nowadays dinosaur reconstructions much more appreciate the musculature those animals most likely had. I was not shrink-wrapping my dinosaurs in my drawings already back in the time before the term was even used in dinosaur paleoart. So, it is a bit ironic that I tend to make the same anatomical mistake in my aurochs reconstructions. 

The bones were surrounded by musculature, which has the greatest impact on the outer appearance of the animal. But the musculature was surrounded by fat tissue, which added a few millimeters to centimeters, by the skin, which added a few millimeters to centimeters, and by hair, which also added a few millimeters to centimeters. This necessarily involves a fair bit of guesswork to the reconstruction. I am always, without exception, unsure how much bulk I should add to the skeleton when doing a reconstruction. The actual shape of the animal would also not always be the same when fully grown, but it changed during the season (fatter during fall, skinnier during the end of the winter) and also across its lifetime as aging individuals get heavier, the bulls in particular. Comparing my recent reconstruction based on manipulating a photo of the Taurus bull Darth Vader III to my model of the Sassenberg bull (go here), I came to the conclusion that my model is probably not accurate. It is too skinny, particularly on the legs and the abdomen, making it a bit difficult to imagine this model as a living being. So I made some anatomical sketches trying to better appreciate the bulk of the soft tissue that surrounded the bones. 

 

The trunk 

The trunk is particularly difficult because even with seeing the ribcage and the curve of the spines in real, it cannot be derived from the skeleton how large the intestinum was. Domestic cattle have very large intestina, giving them the heavy appearance they have. Wild bovines, on the other hand, usually have a waist that narrows caudally (instead of being the centre of the mass). For my sketch, I tracked out a photo of the Store-damme skeleton that I had corrected anatomically using GIMP. The blue line shows what a young but fully grown aurochs might have looked like, similar to young fighting bulls and young wisents. The green line shows what an old bull might have looked like, based on the waist anatomy of old wisent bulls. The red line shows the domestic condition that is exhibited by most domestic cattle breeds. I have no precise anatomical method to come to these lines, I am looking at bovines in flesh and blood, guessing and drawing what I consider anatomically plausible. I am only quite confident that the red line is not plausible for an aurochs, since it is the domestic condition not found in any wild bovine. It also looks quite weird on a trunk as short as in the aurochs. 

 

The head 

 

The outer shape of the head also changes quite with age. Young bulls have a slender head while older bulls are bulkier. That’s why my 2019 model looked a bit juvenile (or actually subadult), its head was too slender. I wanted to do a model more credible for a grown bull this time, but it seems that I still “shrink-wrapped” it. Here are sketches that were done tracking out the London skull in frontal view: 

 

The left one is a “shrink-wrapped” version, the left one a version that I consider more plausible. Again I had no particular anatomical method to come to this sketch, but I tried to appreciate the facial muscles that undoubtedly were there and also the skin and fat tissue. 

The other sketches are based on the skull of the Sassenberg bull: 

 

The sketch on the right shows a “shrink-wrapped”, not anatomically plausible, version. It has a paper-thin skin, barely any facial muscles or salivary glands (that sit behind the lower jaw muscles), and there is barely place for the trachea and the oesophagus. The sketch in the centre is anatomically plausible to me, perhaps for a bull in its prime. The left sketch shows the maximum bulkiness that I still consider anatomically plausible. Old bulls might have looked like that. Looking at my most recent model (here) I think it is closest to the shrink-wrapped version, thus not anatomically plausible. So I added some bulk to the head and neck region with GIMP (and also painted an eye). The result looks much more plausible and life-like, I think: 

 

This shows that some aspects of the aurochs’ life appearance are very hard to strictly derive from the skeleton when trying to be very precise, and that trying to fabricate the “perfect aurochs model” is a continuous learning process. My next model is going to be better. I think I will reconstruct the Vig bull and Cambridge specimen (? cow) next time. 

 

Turning Darth Vader III into an aurochs

I have attempted reconstructing the aurochs by photo manipulation using GIMP on photos of aurochs-like cattle multiple times, but this time I think I might have fabricated the most accurate one I have attempted so far. 

 

I used a photo of Darth Vader III, a Taurus bull that is a son of Londo (F2 Sayaguesa x (Heck x Chianina)) and Laniana (which had a little bit of Lidia in her genealogy), thus is 1/32 Lidia, that I took in the Lippeaue in 2022. I superimposed a photo of the Store-damme aurochs skeleton, which I had previously corrected into an anatomically correct posture on the photo. Then I started to manipulate the proportions and shape of the bull according to the anatomically correctly positioned skeleton. I increased the length of the legs, changed the hump by enlarging it slightly, reduced the length of the dewlap, made the neck slightly longer. For the head, I used a photo of the skull from the Sassenberg bull. I made the snout slightly longer, and the postorbital region of the head. Then I made the bodily morphology more like a wild bovine by reducing the bulk of the waist and belly. All the other aspects of the original bull photo fitted the aurochs skeleton. Honestly, I was surprised that I did not have to change the bull that dramatically. The horns of the original had to be removed with the stamp tool, I replaced it with a horn from the Heck cow Erni of the Steinberg/Wörth lineage that I skewed slightly.

This is the original photo of Darth Vader III: 

 

This is the result: 

 

I am very happy with it. It looks rather plausible and credible for a real (wild) bovine to me, more so than my recent model which is based on the same skeleton and skull: https://breedingback.blogspot.com/2023/04/life-reconstruction-model-of-sassenberg.html 

The photo manipulation shows me the deficiencies of the model, my next one is going to be better. 

 

I think that less-derived Lidia, Spanish fighting cattle, are the cattle that come closest to this reconstruction by far. In my opinion, this phenotype is roughly achievable in “breeding-back”, as long as wild yak, Java banteng and Lidia are in the mix and used wisely. 

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. 

 

The lateral horn orientation

When it comes to the horns of aurochs and cattle, I usually differentiate them into three factors to compare them: the actual shape of the horn, the dimensions (length and diameter) and the orientation relative to the skull. All those three factors can vary among cattle. When thinking of the horn orientation, I only considered the orientation relative to the snout. In the European aurochs, this angle usually varied from 50-80°, with some individuals being exceptions. I did not notice that the horn orientation also has another variable that has quite an impact on how we perceive the horn “shape” (the shape actually does not change, but it appears as if it did when the orientation is changed), what I call the lateral horn orientation. This factor is the orientation of the horn in the plane that is 90° to the sagittal plane of the animal, in other words, the horn orientation relative to the side of the animal. I did not realize the lateral horn orientation is a factor before I did a photo manipulation morphing the Taurus cow Lerida into an aurochs cow, where I had to slightly elevate the lateral horn orientation of the cow in order to make the horns appear more aurochs-like. 

Another good example that the LHO is relevant are the horns of many Sayaguesa. Looking at the head of one of the Sayaguesa cows grazing in the Lippeaue, at first glance one would say the horn tips do not face inwards enough because they point right towards the sky and that the primigenius spiral is not present: 

But elevating the LHO, so that the proximal half of the horns do not point downwards but slightly upwards, an aurochs-like horn curvature with the primigenius spiral appears (the shape of the horn was not changed, showing that it already had an aurochs-like shape): 

So I did a sketch playing around with the LHO: 

 

I sketched an aurochs horn that I copied and mirrored, and positioned with a different LHO four times. The uppermost sketch shows a LHO rather elevated, as can be seen in the skull fragment of Asti and Gramsbergen (both likely belonged to cows). The second one counting from the top shows the LHO slightly elevated, as exhibited by the vast majority of aurochs skulls (f.e. the Sassenberg bull, the Nagybajom bull etc.). The third one shows the LHO in a horizontal position, seen in for example the Arezzo skull, some Lidia, some Maronesa, some Sayaguesa bulls. The fourth shows the LHO oriented downwards, a condition that did not appear in the wildtype (at least no skull with such a horn orientation has been found so far), but is found in many Lidia and many Sayaguesa. 

 

Looking at the horns of the, in my opinion, most aurochs-like “breeding-back” population, the Taurus cattle from the Lippeaue, it turns out that their LHO could be more elevated, as seen in the Lerida example. Watussi might improve this a bit. The Hungarian Taurus population from Hortobagyi, which has influence from Watussi, indeed has a more elevated LHO on average, but there is also Steinberg/Wörth Heck cattle and Hungarian Grey cattle in the mix. Wild yaks would help as well, perhaps better than Watussi as their horns are identical to those of the European aurochs. 

 

Crossbreeding proposal: Chianina-Watussi

Chianina are famous for their large body size with sometimes long legs, Watussi are for their very large and thick horns. Now we know that the original aurochs phenotype was very large with mostly large to very large horns (go here for a post on particularly large-horned aurochs). I think the combination Chinaina-Watussi bears potential for achieving cattle that are both large and large-horned and even more than that. 

The problem is that Chianina is large but very small-horned, and Watussi is large-horned but small. Both horn size and body size are quantitative traits which are controlled by many different genes that all have a more or less large or small impact on the final phenotype. That means that if one wants the result of cattle that have the Chianina body size but not horn size, and the Watussi horn size (or slightly smaller) but not body size, the breeding must use the second Mendelian law, otherwise the breeding takes forever. And most likely a larger number of individuals is required, not only a couple of individuals but rather herds of 20-30 (which happens to be the natural Bos primigenius herd size). So at first, a herd of Watussi x Chianina should be produced, as many individuals as possible. The phenotype of the F1 individuals is completely irrelevant as it is the result of maximum heterozygosity, thus combinations of alleles that will not be present anymore as the population becomes genetically stabilized. Both horn size and body size will be somewhat intermediary between the parental breeds, but that is not really relevant yet. It’s the second generation, the F2, where the phenotype of the animals becomes relevant. So a herd of F2 Watussi x Chianina should be produced. Some will have an indicine hump (probably), some will not. Some will have smaller horns and smaller body size, some will have large horns but small body size et cetera. As the focus is on creating a population of large cattle with large horns, only those F2 that have large horns and body size should be chosen for further breeding. 

It is even possible that the combination Watussi-Chianina has potential for a correct wildtype colour with at least some degree of sexual dichromatism. This may sound counterintuitive when two breeds are crossed that both have no visible sexual dichromatism and one is completely white and one is homogeneously reddish-brown. But one should consider the genetics of the two breeds. Chianina has the wildtype allele on the Extension locus, but the colour is diluted by at least two dilution alleles. Watussi does not have these dilution genes, otherwise it would not have that strong expression of red pigment – it has a mutation on the Extension locus that disables the production of black pigment. So a F2 combination of both has the potential for individuals that have the Extension wildtype allele and the production of both black and red pigment enabled. A hint for that is the colour phenotype of the Watussi x Chianina cow of the Auerrind project: 

 

© Claus Kropp 

It clearly has the wildtype Extension allele expressed (it is dominant over the recessive mutation disabling black pigment) and the colour is barely diluted if at all (possibly because some of the dilution alleles of Chianina are recessive). So a F2 of this combination could potentially result in, among other colours, wildtype colour that is not diluted. Sexual dichromatism is possible as well because Chianina might have some degree of sexual dichromatism or even a very strongly expressed one, masked beneath the dilution factors resulting in a white colour in both sexes. That possibility is there since some Sayaguesa x Chianina bulls produced in the Lippeaue had a perfectly black wildtype colour while the cows are always lighter in colour. Therefore, there is at least the chance to achieve aurochs colour from two breeds which do not have aurochs colour at all, because of the genetic background of the colours of the parental breeds. 

In the F2 Chianina x Watussi generation, I would pick those that are large with large horns for further breeding. Some of them might have indicine traits such as the fleshy indicine hump or hanging ears, and the body morphology might not be completely taurine because of the more or less high portion from Watussi. That is why I would backcross the F2 with good Chianina again. And, as you can surely guess by now, create an F2 of this backcross generation. Creating true F2s is the most important step for genetic reasons. The backcross generation might look quite good already, but it will have a full set of Chianina chromosomes. That means they are heterozygous for all the optically good traits and will pass on the alleles for small horns and various colour dilutions. By using the second Mendelian law that applies to a true F2 generation, these alleles can be selected out much more easily than by conventional breeding. So, in the F2 of the Chianina x F2 (Chianina x Watussi), I would only continue to breed with those individuals that are large, have a taurine morphology and large horns, and – as far as possible – also a correct colour. From this selection event on, I would continue to breed with the suitable individuals from that combination in a conventional fashion otherwise the gene pool might become too narrow. It is even possible that not only body size, horn size, colour and morphology of this population is good but also the horn shape, as Chianina often have forwards-facing horns with sometimes a useful curvature. 

 

This scenario takes four generations (8-10 years) and might result in very satisfying individuals that will pass on the desired traits more or less reliably. 

 

 

Would it be crazy to use hybridization in "breeding-back"?

As my readers will know, I suggested cautious hybridization with extant wild bovines that would add traits hardly achievable using domestic cattle only in “breeding-back” in a couple of my posts, after I initially opposed that idea. In this one for example, I suggest using wild yaks in “breeding-back”. But the Java banteng would add value as well, and using both in cautious doses would be add all of the traits that are difficult to achieve with domestic cattle only. The kouprey, which would add all the desired traits both the wild yak and banteng would add and has a slightly more aurochs-like morphology, unfortunately is not available for hybridizing as it is most likely extinct. To give a quick summary of the benefits the wild yak and the Java banteng would add to “breeding-back”:

Wild yak: 

- Very large, up to 205 cm withers height in bulls what equals the large size of European aurochs; difficult to achieve with domestic cattle only, where the upper height limit might be roughly 180 cm; well-marked size dimorphism between the sexes 

- Perfectly aurochs-like horns in both sexes. The horns of the wild yak are really identical to those of the European aurochs in terms of size, curvature, orientation to the skull and even colour. They have a very pronounced inwards-curve which is lacking in most aurochs-like cattle 

- They have a large shoulder hump and a long snout, two traits which are rarely as expressed as in the aurochs in domestic cattle 

- The physiological fitness is higher than in domestic yak and most likely domestic cattle 

- The food choice overlaps with that of cattle/aurochs, they are predominantly grazers 

Java banteng:

- A very well-marked colour difference between the sexes that is always present. This is extremely rare in domestic cattle as domestication reduces sexual dimorphism

- Aurochs-like body size (up to 190 cm which is not quite as large as wild yaks but still significantly larger than most domestic cattle) 

- Roughly aurochs-like morphology (hump, short trunk) 

- It ecologically overlaps with cattle/aurochs, although they browse more, including fruits 

 

Cautious hybridization and wise selection might thus speed up the process of achieving an aurochs-like animal significantly and might have a better end result. But there are, as one can imagine, objections against hybridizing with other species, which I shared until recently. Those objections are two main ones: 

 

Argument #1. A different species would add many undesired, non-aurochs traits, some of which are practically invisible and thus hard to select against, which might distort the authenticity and ecologic suitability of the results. 

There is valid truth to that argument. For example, wild yaks are adapted to higher altitudes than the aurochs, which was a lowland animal, and have larger lungs. They are also adapted to more severe cold, having fewer sweat glands and a different pelage. Also, there are skeletal differences, such as a different vertebrae count. Wild yaks also browse less than cattle/aurochs as they are more strict grazers. Banteng are adapted to a much hotter climate and browse more than cattle. There are also behavioural differences in both species. Yaks, for instance, have a different aggression display behaviour by presenting their large tail tuft, while banteng rely more on display in intraspecific competition than fighting head to head like cattle/aurochs and wild yaks. 

However, it is not impossible to get rid of these undesired behavioural, ecological and morphological traits. The solution might be absorptive breeding while running a strict selection regime. That means that each hybrid generation would be backcrossed with taurine cattle, but only those hybrids that still have retained the desired traits added by the species would be kept for further breeding. After eight generations, for example, the genealogical portion from the other species would be as low as 0,3%, therefore there would be a high chance that the undesired traits are washed out while the desired ones remain in the population when selected appropriately. 

 

Argument #2. “Breeding-back” cattle with a tiny but important bit of introgression from wild yak and Java banteng would not be pure domesticated aurochs anymore. Thus, the argument that “breeding-back” cattle are a native species in European nature would be gone, as they would more or less be hybrids. 

There are two problems with this objection. On a more general note, introgression between closely related species at some point of time has been found everywhere it was looked for in mammals, including our own species Homo sapiens, so it seems that hybridization (or more precisely, introgression) is a very widespread phenomenon in the process of speciation and evolution in general. In the case of wild bovines, Cambodian banteng have introgression from the kouprey, wisent have homeopathic introgression from aurochs and there may be more cases which we are currently not aware of. So introgression per se is not “unnatural”, quite the contrary. Furthermore, it is not technically true that domestic cattle are “pure” albeit domesticated aurochs. Domestication itself is an anthropogenic process, resulting in organisms that differ from the wildtypes that were shaped by nonhuman evolution. A wild aurochs’ genome is 100% wild aurochs. A domestic cattle genome is 100 - x % wild aurochs, x being the portion of the genome that is made up by alleles that mutated after domestication. I do not even dare to speculate how large or small that portion is, and it is certainly different from breed to breed to a certain degree. Thus, domestic cattle are not “pure” aurochs, but rather partly wild aurochs and partly a domestic mutant. So, the originality of the aurochs is gone as a result of domestication anyway. If another species is bred in, the non-aurochs portion would increase dramatically in the first couple of generations, but decrease in the advanced generations as a result of absorptive breeding. It is even possible that, when selected wisely, the aurochs portion could actually increase by introgression from wild yak and banteng. I say that because I consider it likely that, as long as the aurochs-like traits in wild yak and banteng are not the result of convergent evolution (which I do not consider particularly likely), these traits are caused by the same wildtype alleles as in the aurochs. For example, the identical horn curvature between aurochs and wild yak might be caused by alleles shared from a common ancestor. Introgression might reintroduce these alleles into the domestic cattle population. The same could be the case for the sexual dichromatism in the Java banteng. In this case, introgression would reintroduce wildtype alleles found in the aurochs which are absent or at least very rare in domestic cattle. So the “genetic purity” argument is not convincing to me. Apart from that, the introgression might also introduce physiological fitness-related alleles from banteng and wild yak which are superior to those of domestic cattle in terms of physiological fitness, thus providing an advantage for “breeding-back” cattle compared to the domestication-induced disadvantage that domestic cattle usually might have. 

 

Therefore, I think small doses of controlled hybridization/introgression from the two wild bovines most suitable, and subsequent wise selection, is not a crazy idea at all and could be very beneficial for the ecologic and phenotypic goal of “breeding-back”. What would be crazy, on the other hand, would be hybridization without a plan and without strict selection.