How to breed for the right sexual dichromatism?

The sexual dichromatism, the difference in colour between the sexes, is one of the most defining characters of the wild aurochs. A reduced or absent dichromatism is a typically domestic trait. Thus, “breeding-back” definitely has to try to achieve a well-marked sexual dichromatism.

 

Aurochs calves were born of a reddish chestnut brown colour, and grew their adult colour in their first year. The reddish brown base colour becomes superseded by black hairs that steadily increase in number. This darkening of the coat starts on the head and neck, the legs and ventral side of the trunk. I call this darkening of the coat the process of eumelanisation (eumelanin is the black pigment in mammals). When the eumelanisation is completed, the whole body is black except for a lightly coloured dorsal stripe and mouth. This was the colour of the bulls. Bulls with a colour saddle did very likely not exist in the European subspecies (go here). In cows, the eumelanisation is stopped earlier. Depending on the degree of eumelanisation, cows can display a wide range of colours which I illustrated in the drawing down below: 

 

I am not so sure about the top left phenotype, but the other phenotypes are proven for aurochs cows based on cave paintings and historic records. It has to be noted that bull-coloured cows are reported to have been very rare. 

 

In wildtype coloured cattle (cattle with a phenotype caused by the E⁺ allele on the Extension locus) we have the same mechanism. The difference is that in most breeds domestication has caused a chaos regarding the degree of eumelanisation: some breeds are bull-coloured in both sexes, such as Sayaguesa where the cows are bull-coloured in many cases, or the dichromatism is at least reduced by bulls having a colour saddle, such as in Alistana-Sanabresa, or both sexes have a very reduced eumelanisation, such as Cachena and Barrosa, for example. Only some breeds have retained the dichromatism we see in the aurochs, such as Maronesa (the bulls are always black, and most cows are less eumelanised than the bulls), or the old lineage of Corsican cattle, which is almost extinct due to crossbreeding with more productive breeds. In those two breeds, all the alleles involved in the production of the colour are very likely the original alleles of the aurochs otherwise we would see a different phenotype. 

The genetic background of the sexual dichromatism found in Bos primigenius is not resolved yet. The genetic program of the eumelanisation process can be located anywhere on the genome. The degree of eumelanisation is said to be dependent on the testosterone level. Bull calves that get castrated before they grow their adult colour grow the colour of cows. This explanation, that eumelanin is only dependent on testosterone level, cannot be the whole story, however, as this would mean that a Sayaguesa cow (which usually is more or less fully eumelanised) has more testosterone than a Barrosa bull (which is barely eumelanised), which is very implausible. Consequently, it must be the alleles that regulate the degree of eumelanisation that mutated in these cattle, with some alleles needing a higher level of testosterone (resulting in less eumelanised sexes) and some alleles needing a lower level of testosterone (resulting in bull-coloured cows) to become active. This is a speculation, but the only plausible one to me. 

 

How to breed for a well-marked sexual dichromatism as in the aurochs? Crossbreeding shows that trying to reduce the eumelanisation of bull-coloured cows by crossing in a less eumelanised breed does not increase the degree of sexual dichromatism. This has been shown in the Sayaguesa herds of Peter van Geneijgen, who incorporated individuals influenced by Alistana-Sanabresa, a less eumelanized breed. The results were less eumelanized cows (thus with “cow colour”), but also in some bulls having a colour saddle. Thus, the sexual dichromatism did not increase, even though some cows are now correctly coloured. 

This tells us that working with two breeds which have a reduced sexual dichromatism cannot result in an increased sexual dichromatism. One would have to take a breed with the right alleles having the right sensitivity for testosterone, if my assumption above is correct. Thus, the right sexual dimorphism can only be achieved if there is a breed that already has it. Luckily, this is the case as there are at least two breeds in Europe with that trait (Maronesa and Corsican cattle). 

 

There are “breeding-back” herds that have a satisfying degree of sexual dichromatism. For example, the Hellabrunn Heck herd has a excellent colour and dichromatism (go here). I evaluated the sexual dichromatism in the Lippeaue population using a photo archive (go here). The result was that more than 80% of the individuals have the right degree of eumelanisation for their sex. Of course some individuals that are correctly coloured might pass on individuals with no sexual dichromatism, f.e. bull-coloured bulls that pass on bull-coloured cows or cow-coloured cows that pass on bulls with a saddle. In order to increase the sexual dichromatism, it would have to be possible to discriminate between those individuals and those that pass on sexual dichromatism, which is hitherto impossible as the genetic background of this trait is not resolved. 

Heck cattle have their sexual dichromatism from Corsican cattle, and Taurus cattle has it from Heck cattle (Chianina might contribute an at least moderately developed dichromatism as well, it could be masked beneath the dilution alleles producing the white colour). 

 

Achieving a well-marked sexual dichromatism might become problematic for the Tauros Programme and perhaps also the Auerrind project. Many Tauros cows are rather dark and bulls often have a saddle, and most of the founding breeds have a more or less reduced sexual dimorphism (Maremmana, Highland, Sayaguesa, Podolica, Boskarin, Pajuna), they use Maronesa only on a small scale in the form of four cows and a few bulls in Dutch herds as far as I am informed. For the Auerrind project, all of the founding breeds have a reduced sexual dichromatism (Sayaguesa, Watussi, Maremmana, Hungarian Grey, Pajuna, perhaps Chianina). So far, not enough crossbred animals have been produced to judge the sexual dichromatism in the Auerrind herds. 

 

The last free-ranging horses in Europe were hybrids

EDIT: The individual examined in the study is actually the Shatilov tarpan, a specimen which was also caught in the Cherson region but died in 1868. 

The nature of the horses described in contemporaneous literature from previous centuries, such as by Gmelin, Pallas, Smith and others, has long been dubious. It was unclear if those horses were genuine wild horses, feral domestic horses or hybrids. In the Russian steppe, these free-ranging horses of the 18th to the early 20th century were called "tarpans". 

The fact that a black dun colour prevailed in these historic reports may suggest that these horses were at least partly wild horses, because black dun or black was the prevalent colour of late Holocene European wild horses. However, the fact that also non-wildtype colours were mentioned in these reports suggests admixture. The mane of the last free-ranging horse of the Russian steppe was described as being semi-erect, as to be expected from a hybrid between a horse with an upright mane and a falling domestic mane. 

The Cherson Tarpan, photographed in 1884

Librado et al. 2021 examined the genome of the so-called Cherson Tarpan, the only "tarpan" to be photographed. It revealed that at least this individual has a hybrid origin of western wild horses and domestic horses. To be precise, the authors write: "The tarpan horse came about following admixture between horses native to Europe [...] and horses closely related to DOM2". A hybrid origin for the free-ranging horses described in historic references makes sense. That they were pure wild horses was unlikely due to their phenotype (domestic colour variants et cetera). That they were merely feral horses was also unlikely because black dun prevails in these reports, and it would be a big coincidence if feral domestic horses also were mainly black dun in colour. Also, I have always considered it the most likely scenario that the pure wild horse did not die out as a whole but got continuously genetically influenced by feral domestic horses. So it seems that this scenario is confirmed, at least under the assumption that not only the Cherson tarpan but all the other free-ranging horses of Europe during the 18th to 20th century were hybrids. 

The information that the horses historically called "tarpans" might help to stop the inappropriate synonymization of the word "tarpan" with the original European wild horses. 

The study's main purpose was the origin of the domestic horse. They conclude that the domestic horse most likely originated in the lower Volga-Don region, and that mutations on two genes were of particular importance for the domestication of the horse: one on the GSDMC gene, probably improving the horses' ability for bearing weight on their back, and one on the ZFPM1 gene, probably reducing the fear response and increasing the docility of the horses. 

The study, however, completely ignores the work of Taylor et al. 2021 that concluded that the Botai horses were not domestic. 

Literature: 

Librado et al. 2021: The origins and spread of domestic horses from the Western Eurasian steppes. 2021. 

Five common myths about Heck cattle

I already did a post on myths about Heck cattle in 2013 (go here). But that post fails to address the most prevailing myths or misconceptions about Heck cattle that I want to outline with this post. 

 

Myth #1: Heck cattle are aggressive. This is a very annoying myth, because it simply is not true. I made a post on that a few weeks ago. It is based on one incident that is repeated over and over, yet that incident is the only documented case of some Heck cattle individuals behaving aggressively. Heck cattle are used in numerous grazing projects, are bred on private farms and zoos, and there have been no further incidents of Heck cattle attacking people without a reason. Heck cattle is generally described as a rather unproblematic breed by breeders [1,2]. I can confirm from my personal experience that Heck cattle are not an aggressive breed. 

 

Myth #2: Heck cattle were bred using the Spanish fighting bull. I made a post on that common misbelief years ago. Many people that are only half-educated on this breed believe it was bred using the Spanish fighting bull. That false claim is even made in otherwise very well-researched sources [2]. While it is true that Lutz Heck has used Toro de Lidia in his crossbreeding experiments, it is also true that none of his stock survived past 1945, so that modern Heck cattle exclusively go back to the stock of Heinz Heck, who did not use that breed. 

 

Myth #3: Heck cattle were created by the Nazis. This is another very annoying myth. The claim that it was Nazi officials that ordered the creation of Heck cattle is just plain wrong. The Heck brothers started breeding in the 1920s and their motivation was purely zoological. It is true that Hermann Göring sponsored Lutz Heck’s experiments and allowed him to spread his cattle among German game parks, but it is also true that Heinz Heck, whose stock is the basis of modern Heck cattle, was opposed to the Nazi regime. That’s the whole story. Yet a lot of people make a huge deal of it, because “Nazi cows” is simply too entertaining for some individuals. 

 

Myth #4: Heck cattle look like the aurochs, just smaller. This is a claim that is objectively wrong. I reviewed the quality of Heck cattle as a “breeding-back” result in this 2013 post. Heck cattle are noticeably different from aurochs on many aspects, not only the size. See down below for a drawing that illustrates the optical differences between aurochs and cattle: 

 

Myth #5: The Berlin lineage and the Munich lineage looked identical, proving the success of the Heck brothers’ experiments. This myth also occurs from time to time and was created by the Heck brothers themselves. They claimed their results looked the same, although they used different breeds, what, according to them, proved that they did their work right. This is far from the truth because Lutz and Heinz Heck’s cattle did not look very similar. Lutz Heck’s cattle were greatly influenced by the Spanish fighting bull, while the cattle of Heinz Heck were heavier and also the horns were different. I do not know why the Heck brothers thought their cattle looked identical, it clearly was wishful thinking. 

 

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. 

 

 

The wild zebu, B. p. namadicus

I did a couple of posts on the Indian aurochs, B. p. namadicus, the ancestor of the zebu, previously. Go here or here. 

Recently I did another artwork for the Indian aurochs or wild zebu. I think this new artwork is the most accurate for this subspecies I have done so far. 

The head and horns are based on the cranial material you can see in the second post I linked above. The horns are proportionally large, and more wide-ranging than in the European subspecies. The skull is narrower with less prominent eye sockets. 

As to the body, I was unable to find any information on the postcranial anatomy of B. p. namadicus. But it is very likely that it had a standard wild cattle anatomy, such as a short trunk, long legs and a hump formed by tall processus spinosi. I speculate that the dewlap of the wild zebu was longer than in the European aurochs B. p. primigenius, because of thermoregulation and its possible display function. The ear shape is based on zebus. And it is not unlikely that it lacked the curly hair between the horns that the European aurochs had, since tropical bovids usually do not have hairy ornaments and no zebu has curly hair on the forehead. The colour is speculation, for this artwork I assumed that it had the same colour as the European aurochs. 

It is not totally impossible that the Indian aurochs or wild zebu had a zebuine hump made of muscles and fat just like zebus. There are no osteological correlates between the zebuine hump and the skeleton, so that we cannot deduce its presence or absence based on the bones. Furthermore, there are no artistic depictions of B. p. namadicus that could provide a clue. For this artwork, I assumed that it did not have a fleshy zebuine hump. 

How much introgression from wild aurochs was there in Europe?

Taurine cattle were domesticated in the Fertile Crescent in the Near East. As “breeding-back” focuses on the European aurochs, it is an important question how much introgression from local aurochs populations into the domestic gene pool there was in Europe. Especially as some claim “breeding-back” is doomed to fail because it focuses on the European type while domestic cattle descend from the Near Eastern aurochs. 

 

To assess the question if there was local influence from European aurochs into the modern taurine cattle population, the genetic evidence has to be taken into account. The mitochondrial DNA tells us about the possible matrilineal introgression from local aurochs. There were two separate mitochondrial groups of European aurochs, Bos primigenius primigenius. Southern European and Near Eastern aurochs share the mitochondrial haplotype T, which is also found in most domestic cattle, while Central, Northern and Eastern European aurochs have the haplotype P [1]. The P haplotype was discovered in Holstein cattle and the Korean Hanwoo [1,2], what suggests introgression from wild cows of the northern type. Some Italian breeds also have the haplotypes R and Q, which are unique among domestic cattle [3,4]. This suggests local introgression or even domestication of wild aurochs in Italy [4]. 

Regarding the patrilineal evidence, it has been suggested in 2005 that introgression from aurochs bulls into domestic cattle was common in Europe [5], which was refuted later [6]. 

It has to be kept in mind that mitochondrial and Y-chromosomal haplotypes only tell half of the story. The mitochondrial genome is passed on by the mother exclusively, and the Y chromosome only by the father. Thus, looking only at mitochondrial or Y-chromosomal haplotypes can be misleading. If aurochs bulls mated with domestic cows, which is not unlikely as cattle were kept free all year round in earlier times (and still are today in some regions of Europe), which is also historically documented to have happened (Anton Schneeberger mentioned that occasionally wild aurochs bulls covered domestic cows in the 16^th century), and if only the female offspring was kept for further breeding (which is also not unlikely because the behaviour of the hybrid bulls was certainly more problematic than that of the cows), the wild influence would be undetectable by mitochondrial and Y-chromosomal haplotypes. The aurochs would not pass on aurochs mtDNA, and the Y-chromosome would be selected out in the first generation. Thus it is possible or even likely that introgression from local wild aurochs was more common in Europe than suggested by mitochondrial and Y-chromosomal haplotypes. Therefore, not only these parts of the genome should be considered to look for local aurochs introgression, but also the autosomal genome. 

Not surprisingly, when the first nuclear aurochs genome was fully sequenced [7], it was found that British aurochs significantly influenced British and Irish landraces [7,8]. 

 

Therefore, hybridization between local aurochs and domestic cattle not only happened occasionally, but the offspring was actively included into the breeding by ancient farmers. It is possible that the influence of local aurochs contributed alleles useful for the breeding, f.e. adaptions to local climate and diseases that were beneficial for the cattle from the Near East. Consequently, modern European taurine cattle are not only the descendants of the Near Eastern aurochs, but also of the European aurochs. The European aurochs left living descendants. 

 

 

Literature 

 

[1] Mona et al.: Population dynamic of the extinct European aurochs: genetic evidence from a north-south differentiation pattern and no evidence of post-glacial expansion. 2010. 

[2] Zhang et al.: Evolution and domestication oft he Bovini species. 2020.

[3] Park et al.: Genome sequencing of the extinct Eurasian wild aurochs, Bos primigenius, illuminates the phylogeography and evolution of cattle. 2015.

[4] Bonfiglio et al.: The enigmatic origin of bovine mtDNA haplogroup R: Sporadic interbreeding or an independent event of Bos primigenius domestication in Italy? 2010. 

[5] Götherström et al.: Cattle domestication in the Near East was followed by hybridiziation with aurochs bulls in Europe. 2005. 

[6] Edwards et al.: Mitochondrial DNA analysis shows a Near Eastern Neolithic origin for domestic cattle and no indication of domestication of European aurochs. 2007. 

[7] Orlando, L.: The first aurochs genome reveals the breeding history of British and European cattle. 2015. 

[8] Park et al.: Genome sequencing of the extinct Eurasian wild aurochs, Bos primigenius, illuminates the phylogeography and evolution of cattle. 2015. 

 

Is Oostvaardersplassen a "new wilderness"?

I covered Oostvaardersplassen multiple times on this blog, but never the ecologic dimension of the reserve as a whole. Oostvaardersplassen is often praised as a new wilderness, f.e. in the documentary “De nieuwe wildnernis” from 2013. Others have claimed it is a failed case of rewilding. 

 

Oostvaardersplassen, located in the province of Flevoland in the Netherlands, is a fenced area of 56 square kilometres. In 1983, 35 Heck cattle were introduced, followed by 27 Konik ponies in 1984 and 54 red deer in 1992. The number of the animals was not regulated and there also was no supplementary feeding. In the early 2000s, the number of cattle reached its peak of about 1000 animals, and after that, started to decrease again while the number of horses and red deer started to increase further. As of October 2017, there were 230 Heck cattle, 1040-1060 Koniks and incredible 3910-3990 red deer in the reserve (go here). It has to be noted that the largest carnivore in the reserve is the fox, while there are no lynxes, bears, wolves and of course no lions which would be the natural enemies of grown bovines and equines. 

What is very interesting is the drop in the number of cattle. It is very likely that the cattle are outcompeted by geese [1] and possibly also horses, because both can graze a few centimetres deeper than cattle [1,2]. I would not rule out that the cattle may one day disappear from the reserve because of that. If that is the case, how did aurochs coexist with these animals? One possible explanation would be so-called predation-mediated coexistence. Adult aurochs were possibly less easy to kill for wolves and even lions than horses or deer. Thus, these predators would reduce the population of these animals more than that of the aurochs, and therefore enabling coexistence between these species. 

Roe deer already disappeared from the reserve, perhaps outcompeted [3] (that’s what the literature says; however, I recently saw a video from OVP that shows a roe deer in the reserve). 

 

The original natural population density of large herbivores in Europe without human influence is unknown. But the fact that the avifauna in the OVP has declined by 36% since 1997 [3], as well as the drastic reduction of cover from woody vegetation from 30% to less than 1% from 1996 to 2011 [4] may suggest overgrazing in OVP. 

 

The OVP should be regarded as an artificial system rather than a nature area, in which some of the native large herbivores are present (red deer, cattle, horses) and others are not (roe deer, wild boar, elk, wisent) [4] and, more importantly, no predators for adult deer, cattle and horses. Because the area is fenced, the large herbivores are unable to migrate and the area is basically an island – an island devoid of predators. The reduction in avifauna diversity and decrease of habitat diversity in the reserve as a consequence of the intense grazing pressure caused by the very high density of the herbivores as a consequence of the lack of predators, as well as the disappearance of roe deer from the reserve suggest that the OVP anything but a “natural” ecosystem. It is as if one would fence an area in the Serengeti, kill off all the predators, watch some herbivore species reaching very high densities while others disappear, and a loss of habitat types and an accompanying loss of species diversity in that area. 

In the Yellowstone reserve, the reintroduction of wolves has shown to have an impact on herbivore activity and population density, which in turn influences the vegetation [5]. A reintroduction of predators in the OVP is unfortunately out of question, as the surrounding area is densely populated and farmers would have to fear for their livestock. 

 

Some consider the OVP because of all that a “failed case of rewilding”. Regardless of if this is true, it is still very valuable as a dedomestication experiment. There are hints that the Heck cattle population in the OVP, which has been exposed to selective pressure for 40 years now, is evolving (go here or here). 

 

Literature 

 

[1] Cornelissen et al.: Rewilding Europe: Early dynamics of a multispecies grazing ecosystem.

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

[3] van Vuure: On the origin of the Polish Konik and its relation to Dutch nature management. 2014. 

[4] Cornelissen et al.: Effects of large herbivores on wood pasture dynamics in a European wetland system. 2014.

[5] van Vuure: Retracing the aurochs – history, morphology and ecology of an extinct wild ox. 2005. 

 

 

 

Why were the last aurochs less impressive than earlier ones?

Species change over time, evolution is inevitable. Apparently the European aurochs, Bos primigenius primigenius, on which the guideline of “breeding-back” is based on, also changed over time. It got continuously smaller towards the end of its existence, and also its horns became smaller and less curved. Basically, these changes made the last European aurochs less impressive than those of the early Holocene. But why is that, and which type of aurochs (the impressive Early Holocene aurochs or the not so impressive aurochs of the Jaktorow forest) should “breeding-back” focus on? 

 

The size decrease 

 

Late Holocene aurochs were smaller than Pleistocene and Early Holocene aurochs. Some authors assumed a dramatic size decrease so that the last aurochs were merely as large as domestic cattle [1]. This is certainly incorrect. There is no evidence for aurochs bulls considerably below a withers height of 160 cm. The shortest withers height for a male aurochs described in the literature is 154 cm [2]. Considering the fact that soft tissue and hooves would add to the height in the living specimen, it might have been 159 to 165 cm tall in life. There are several Holocene aurochs specimen that exceeded a height of 170 and 180 cm in bulls and reach 165 cm in cows [2], and also historic reports from the 16^th century describe the aurochs as “much larger than cattle” (Schneeberger) or “huge” (Swiecicki) [3]. Van Vuure (2005) summed up all credible references for aurochs size and concluded that Holocene bulls were 160 to 180 cm tall at the withers, and cows 150 cm, and Pleistocene specimen were on average 10 cm taller [3]. 

Nevertheless, aurochs got smaller during the Holocene. Pleistocene remains suggest aurochs of a very large size, such as the oldest aurochs skull found or a huge skull with a length of 91,2 cm [4], which suggests a specimen that easily surpassed 200 cm withers height (sounds huge, but some wild yaks also reach 205 cm). The Prejlerup bull skeleton from Denmark from the early Holocene reaches 190 cm withers height, what means that in life the bull probably was between 195 to 200 cm tall. That means that early Holocene northern European aurochs at least occasionally reached heights this large. Later finds do not reach this size anymore. 

How large the last aurochs at Jaktorow were is unknown, since there is no height data for them. But Schneeberger mentioned that they were still much larger than domestic cattle. 

 

The decrease in horn size 

 

Pleistocene aurochs not rarely had huge horns. The earliest aurochs skull found has horn cores of a length of 112 cm (external length of the horn core) [5]. In the living animal, the horn sheath would add to the length, a few centimetres at least, a few decimetres maximum. A Pleistocene skull from Germany has a horn core length of 92 cm, another skull from Italy a horn core length of 120 [4]. Again, the sheath would have added to the horn length. Holocene bulls still had occasionally large horns, such as the Sassenberg specimen, but smaller-horned bulls began to appear, such as the Prejlerup, Himmelev or Önnarp specimen. 

The horn of the last reported aurochs bull which died in 1620, however, is rather meagre in comparison. It measures only 46 cm, is slim and not as curved as earlier horn sheaths. The age of the bull is not recorded, so that it could have been not fully grown at the time of its death, but to me it looks like a fully grown horn (horns that are not fully grown yet often look a bit compressed in length, while that horn is very slim and stretched). 

So the horns diminished from lengths of possibly 1,5 metres maximum to not even half a metre at the very end of its existence. 

 

So it seems that the very last aurochs from the 16^th and 17^th century were much less impressive than Pleistocene and early Holocene specimen. They were smaller, and their horns not even nearly as huge. It is not unlikely that the trend would have continued till today, so should “breeding-back” focus on the less impressive aurochs, since the aurochs of today would not be 2 metres tall with one meter long horns but much smaller and with comparably meagre horns? Well, let’s have a look at the reasons for why the aurochs got less impressive in historical times. 

 

The reasons for the decrease of body and horn size 

 

When animals change in body size, climatic changes are often the first explanation that comes to mind. The controversial Bergmann’s rule proposes that animals in colder regions are larger than those of warmer regions, because the surface to mass ratio allows larger animals to preserve energy easier than smaller animals. However, the Bergmann’s rule is not undisputed, there are as many examples against this “rule” as there are in favour of it [6]. Nevertheless, the Pleistocene was colder than the Holocene, so maybe this (assuming the Bergmann’s rule is correct) is the reason why Pleistocene aurochs were that large. However, this is not a valid argument, because the distribution of the aurochs changed with the climate. During the cold glacials, the aurochs retreated to the south and was mainly found in Southern Europe and North Africa. Large aurochs were found there, f.e. the large-horned large skull of the oldest aurochs found so far is from Tunisia. Pleistocene Tunisia probably was not colder than Holocene Denmark, for example. Also, climate cannot explain why the size of the aurochs’ horns decreased. 

EDIT: I did not address the role of predators enough. The aurochs evolved under the pressure of predators such as big cats and hyenas in the Pleistocene. These predators died out in Europe at the end of the Pleistocene. It is thus tempting to assume that the lack of large predators that could take down adult aurochs was a factor in the decrease of body and horn size. However, aurochs in North Africa and India were smaller than those of Northern Europe, despite being preyed on by big cats in these ecosystems. Thus it is not likely that the lack of big cats and hyenas was an important factor in the size decrease of the European aurochs. 

If climate did not cause the decrease of the aurochs’ body and horn size, it is important to look at other factors that might have influenced a large European herbivore in the last 10.000 years. These factors are caused by man: habitat limitation and hunting. 

 

It is likely that hunting might have negatively influenced the horn size of the aurochs. Julius Caesar mentions in De bello gallico that the Germanic people hunted aurochs for their horns. Probably trophy hunting was not restricted to ancient Germanic people. Aurochs horns were often used as ornament or drinking horns for the nobility. The larger the horns, the more impressive the trophy. Therefore, it is possible that large-horned aurochs were hunted more intensely than smaller-horned aurochs. It is also known that trophy hunting has lead to a considerable size decrease of the size of tusks of African elephants [7]. The so-called “great tuskers” have become rare, and the portion of tuskless African elephants has increased significantly. 

Habitat limitation also very likely influenced the body size and horn size of aurochs. The habitat of the aurochs was increasingly replaced by agricultural fields and pastures for domestic cattle. The aurochs had less space to live the more the human population grew. The habitat of the aurochs was lessened and fragmented. This leads to the island effect: large species shrink in size because less space and food is available, what increases the evolutionary fitness of smaller individuals. Go here for my post on the aurochs and insular dwarfism. Aurochs were pushed into hideaway regions which were not ideal for the species. Also, the lack of space for the aurochs to thrive might have further increased the reduction of horn size. Growing horns costs energy and minerals, and while horns certainly have a fitness advantage, on a confined space were food and minerals are scarce, smaller horns are more economic than large horns. 

Another factor that might have influenced the genetic structure of the aurochs that should not be forgotten is hybridization with domestic cattle. As the habitat for the aurochs became increasingly limited by pastures for cattle and horses, the wild bovine and its domesticated descendants lived side by side. Recently it has been found that the last aurochs bull had a domestic mitochondrial haplotype, what shows that there was maternal introgression from domestic cows into the last aurochs population [8]. Seemingly, domestic cows either escaped or were stolen from the pastures by wild aurochs bulls, and reproduced with aurochs in the wild. This might have contributed to a decrease of body and horn size, and could have also influenced the horn curvature (what might explain why the horn of the last bull is only weakly curved). 

 

To sum it up, trophy hunting as well as habitat limitation and hybridisation with domestic cattle likely are the cause for the aurochs becoming less impressive, i.e. smaller and with only comparably meagre horns. As to the question on which type of aurochs “breeding-back” should focus, the answer is clear to me: “breeding-back” wants to mimic the extinct ancestor of domestic cattle in its original form as it would exist today if it had not been for human influence. Hunting, habitat limitation and hybridisation with cattle are clearly anthropogenic factors. Without human influence, the aurochs probably would not have changed that much during the 9.000 years since the Prejlerup aurochs died, just as the difference between an aurochs from 100.000 years and one from 110.000 years ago would not have been dramatic if even noticeable in the morphology that is accessible to us. Therefore, I think it is definitely legitimate if “breeding-back” aims for 1,9 or even 2 metre tall cattle with 1,2 meter long or larger horns (if that goal is achievable with domestic cattle only is another story). The size goal for the bulls in the Auerrind project, for example, is 170 to 180 cm as Claus Kropp stated on Facebook, and that is perfectly in line with the evidence. 

 

Literature 

 

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

[2] Rene Kysely: Aurochs and potential crossbreeding with domestic cattle in Central Europe in the Eneolithic period: A metric analysis of bones from the archaeological site of Kutna Hora-Denemark (Czech Republic). 2008.

[3] van Vuure: Retracing the aurochs – history, morphology and ecology of an extinct wild ox. 2005. 

[4] Frisch: Der Auerochs – Das Europäische Rind. 2010. 

[5] Martinez-Navarro et al.: The early middle Pleistocene archaeopaleontological site of Wadi Sarrat (Tunisia) and the earliest record of Bos primigenius. 2014. 

[6] Wright: The history of the European aurochs (Bos primigenius) from the Middle Pleisotcene to its extinction: an archaeological investigation of ist evolution, morphological variability and response to human exploitation. 2013. 

[7] Nowak et al.: Trophy hunting: bans create opening for change. 2019. 

[8] Bro-Jorgensen et al.: Ancient DNA analysis of Scandinavian medieval drinking horns and the horn of the last aurochs bull. 2018.