The last aurochs hybridized with cattle in the wild

Domestic animals and their wild counterparts are usually able to interbreed freely and produce fertile hybrids. Thus, it is always likely that everywhere they share their habitat, they might interbreed and thus mutually influence their populations. Domestic animals always might escape, and wildtype animals always might leave a track in domestic stock by occasional mating. 

When discussing whether aurochs and cattle interbred in Europe, it mostly concerned the question if local aurochs left a genetic trace in cattle populations. The other way round, domestic cattle influencing local aurochs, was not examined yet. However, I have always considered it very likely that escaped domestic cattle left a trace in European aurochs. It happens everywhere where wildtype and domestic type are neighbouring – you see that in wolves (some colour variants, such as black in wolves, are believed to have been inherited from domestic dogs), in wild boar displaying domestic colour, and it has also been proven for late European wild horses that inherited the emutation from domestic stock (see Pruvost et al. 2011). I see no reason why it should not have happened that escaped domestic cattle interbred with aurochs and left a detectable trace in wild populations. 

This interesting question has now been examined by Bro-Jorgensen 2018. A number of ornamented drinking horns from medieval times or shortly after that are suspected to stem from aurochs because of their shape and size have been genetically analysed for mitochondrial haplotypes and sex. The sample also includes the horn of the last aurochs bull that died in Jaktorow, Poland, in 1620. 

Medieval aurochs drinking horn - large, thick and evenly curved

Horn of the last aurochs bull - smaller, thin and not that curved

All of the horns tested turned out to be from males – considering their shape I would be surprised if turned out otherwise – and most of them have the aurochs haplotypes P. The horn of the last bull and two other drinking horns, however, surprisingly carry the haplotype T, which is widespread among taurine cattle. While the origin of the two drinking horns might not be that clear, it is very likely that the claimed horn of the last aurochs bull is indeed from this population and individual. It is also very likely that the population in Jaktorow was not simply a feral cattle population because of historic reports. Thus, the most likely conclusion is that aurochs of the latest centuries, or at least the remnant population at Jaktorow, was genetically influenced by escaped domestic cattle. As this influence is found on mtDNA, which is maternally inherited, the influence must be from a domestic cow at least. Influence from domestic bulls is of course also possible, but was not examined and domestic bulls probably had a hard time competing with wild aurochs bulls anyway. 

Natural selection would probably eradicate most of the domestic influence, except for factors with little selective pressure on them, such as these mitochondrial haplotypes. Perhaps, if the domestic influence was widespread towards the end of the existence of the aurochs (when space became increasingly limited and thus they often neighboured domestic stocks) there also were aurochs populations displaying domestic colour variants, although no such cases have been reported in historic texts. Domestic cattle influence also shows in American bison, where it is particularly visible in horn shape and size (see here, for example). The horn sheath of the last aurochs bull was comparably small (only 45 in length, which is considerably smaller than the bony cores of earlier aurochs males). Even if it was a young individual at the time of death, most likely the last aurochs population had comparably meagre horns as a consequence of limited resources and trophy hunting, but domestic cattle intermixing might be a further reason. This would also explain why the curvature is not nearly as intense and even as in the older drinking horns (cattle intermixing affects horn shape in wild bovines as the bison example shows). 

This discovery is interesting and totally what I expected and predicted. Questions that are particularly intriguing are how widespread and intense that domestic introgression into local aurochs population was, and how large the influence on the visible phenotype of these aurochs population was. 

Literature 

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

Pruvost et al.: Genotypes of predomestic horses match phenotypes painted in Paleolithic works of cave art. 2011. 

Albatros, the Heck bull, vs. aurochs

When looking through Walter Frisch’s Der Auerochs (2010) I found a photo of the Heck bull Albatros in perfect profile view (the photo is © Walter Frisch, I hope it is ok for Mr. Frisch that I use it here). Let us have some fun with it! 

A profile view photo is pretty useful for a direct comparison with the aurochs. When using a single Heck individual, it is always important to pick one that is a fair representative of the breed. For example, it would not be fair to pick one of the hyper-massive dachshund bulls that are still found in the breed that are not nearly of the same quality as the mean, or to choose an individual that is considerably better than the average. I think that Albatros is a pretty fair choice. It is from the Wörth/Steinberg line bred by Walter Frisch, which is remarkable for having large and well-shaped horns (some of them are excellent, take a look at them here). The Wörth lineage is, speaking of body morphology and size, very typical for Heck cattle on the other hand, so Albatros is very representative of the breed. 

I took my most recent reconstruction of an aurochs bull as a comparison. I introduced this reconstruction in this post and I consider it pretty accurate. So I copied the reconstruction and the photo of Albatros next to each other to same scale. For Albatros, I used a withers height of 140cm, which is pretty average for Heck cattle (bulls of the Wörth lineage are sometimes claimed to reach 160cm, but I do not consider this plausible for Heck cattle, especially since I saw the herd myself), and for the aurochs I used 170cm withers height – 170cm is the mean withers height found within this species. There are populations where bulls reached only about 150cm but also giants with a withers height of about 190cm or more (see How big was the aurochs really?), so choosing 170cm seems fair to me. 

Here you see the comparison of both animals in flesh and below that a comparison of both skeletons (the photo of the Heck bull is suitable to deduce the skeleton of the living animal, it is not as precise as an X-ray but an approximation based on anatomical knowledge – I already did this with several cattle individuals on Comparing skeletons with skeletons). I go over the differences both in morphology and behaviour. 

Skeleton of the Heck bull, deduced from the photo

Skeleton of the Kopenhagen bull

Morphological differences: 

Size.In absolute height, the Heck bull is of course smaller than the aurochs by about 30cm. However, in mass, both animals might be equal. Massive Heck bulls reach a weight of about 900kg [1], which is probably also the upper weight range for aurochs bulls (more on that in an upcoming post). So technically speaking, both animals have the same mass, but distributed differently – an aurochs was built way higher and shorter than most domestic bulls. 

Proportions and skeleton.This is where we have considerable differences. First of all, the trunk of the Heck bull is elongated while the size/length of the limbs shrunk – the ratio of the distance from the hooves to the shoulder blade (note: not withers height) and to the end of the pelvis is exactly 1:1 in the aurochs, and 1:1,13 in the Heck bull. The head size also shrunk dramatically, as much as – most likely – also relative brain volume. The skull shape is clearly paedomorphic – it is shortened, especially the snout, and the eyes are enlarged. Those changes in the skeleton and proportions are typical consequences of domestication that we see in nearly all domestic mammal species that have been domesticated. Also, the length of the processus spinosi in the shoulder area (“hump”) is greatly reduced in the domestic bull – while the spines go well beyond the shoulder blade in the aurochs, they are actually shorter than the shoulder blade in the Heck bull. This is also typical of domestic cattle while humps are universal for wild bovini. The comparison of the two skeletons shows the dramatic differences in the skeletal build of an aurochs bull and a domestic bull. 

Soft-tissue anatomy. The muscling of the Heck bull is reduced compared to a wild bovine, which is especially obvious in the pelvic area. Also, the size of the intestinum increased dramatically, causing a huge belly compared to the wildtype. All in all, the soft tissue morphology of this Heck bull is clearly domestic and as such very reminiscent of what we see in dogs with a certain hormonal disorder (cushing syndrome, see this post). The skin is more flappy, especially the enlarged dewlap, and also the scrotum is elongated. 

Horns.The horn volume (length and thickness) is well within the range of an aurochs. The orientation of the horns relative to the snout as well – in Albatros, the horns curve away from the skull in an 75° angle. The literature gives an average horn curvature of 50-70°, but in reality the spectrum is larger (the largest angle I have seen so far is about 90° in the Vig bull and the narrowest 40° in the oldest aurochs skull). The only difference between Albatros’ horns and that of an aurochs is that the curvature (the “primigenius spiral”) is not intense enough. The horns should curve more inwards. A less intense curvature or a tendency of the horns curving more outwards is also a classic domestication trait for bovines. 

Colour. The colour setting and thus the responsible alleles seem identical to that of the aurochs, with two exceptions – the sexual dimorphism (not only in colour) is considerably reduced, which shows in the light brown shade on the dorsal area of the Heck bull, and it is from a population that also has alleles for domestic colour variants such as white spots or colour dilutions. 

Behavioural differences: 

We have no living aurochs to compare the behaviour with, so we take the typical behaviour of a wild bovine as a reference. 

The fight/flight reaction in this bull is greatly reduced. It is, compared to a wild bovine, very agreeable, docile, tame, trainable and its activity level is lethargic compared to the wildtype. 

Comparing the Heck bull trait by trait with an aurochs, it shows that this animal is actually as domestic as can be, and the similarities to the aurochs are limited to colour and horns*. But that is not to say that the bull Albatros or the breed Heck cattle is a failure from the “breeding-back” perspective, not at all. One could analyse any domestic cattle breed the same way and would get similar results. Domestic cattle are simply comparably removed from their ancestor after 8.000 years of domestication. For details, see the article What breeding back can achieve. 

* I am aware of the fact that this Heck bull is probably able to sustain itself in the wild, which is also true of all landraces and also many derived breeds, and it would also show the same social behaviour repertoire as the aurochs (most likely), which is also true of all living cattle. 

Literature

- Bunzel-Drüke, Finck, Kämmer, Luick, Reisinger, Riecken, Riedl, Scharf & Zimball: Wilde Weiden: Praxisleitfaden für Ganzjahresbeweidung in Naturschutz und Landschaftsentwicklung

From aurochs to cattle: step by step

In the post The real differences between aurochs and cattle I go over the organismic differences between the aurochs and cattle in regards to morphology, development, endocrinology, behaviour and genome. Those differences all are interconnected and were caused by the process of domestication. You cannot alter one factor without altering several others at the same time. Each of those factors, like changes in hormonal activity or development, have a particular impact on the organism. With this post, I want to illustrate these impacts by turning a wild aurochs into domestic cattle step by step. I do not say that these changes evolved in this particular order, rather they evolved more or less at the same time but varying extent, this is just a scheme. Please do not use my drawings without permission.

This is the starting point, a wild aurochs: 

Hormonal changes 

Changes in thyroid hormones not only caused a more relaxed, lethargic behaviour but also reduced limb and head size, making the overall appearance of the animal more elongated. Probably horn size would be affected as well. Also, the animals do not grow to full size anymore. 

Another consequence of hormonal changes, of corticosteroids in particular, would be reduced muscling, a hanging spine and an enlarged intestinum. It becomes apparent that this is the factor that causes the animal to truly look domestic – the deformed skeleton and reduced muscling simply does not look compatible to a wild animal. The drawing above reminds me of a Sayaguesa bull, by the way. 

Developmental delay 

The delay in development causes a phenomenon called paedomorphy, resulting in a calf-like skull morphology, shortened horns and reduced sexual dimorphism. Also the shrinkage of the hump might be caused by developmental delay. A lot of cattle landraces, like Rhodopian short horn for example, look like this drawing. 

Pleiotropic effects 

Genes affecting behaviour also affect other factors, such as coat colour. As a result, the animals will start to show spotted colour because the activity of pigment cells is distorted. Furthermore, horn shape is affected as well, they start to curve more upwards and outwards as in all domestic bovines. 

New mutations 

New mutations for new phenotypic traits evolve. Such as for changes in horn shape or curvature, horn size (smaller or larger), stubby legs, shortened snouts, overlong hair, curly hair all over the body, and a whole palette of new colour mutations. The skin also gets more flappier with enlarged or elongated appendages. Cows evolve a dramatically enlarged udder as a result of direct selection on this trait. 

Adding all these factors, we get the domestic cattle that we have today. 

 And here is an animated GIF for this transformation: 

For deeper background information, see these posts: 

- The real differences between aurochs and cattle 

- The Dedomestication series 

- The genetic and developmental background of visible traits