Cattle, aurochs and brain volume

Domestication goes hand in hand with certain changes in morphology, physiology, genetics and other aspects. These changes are very similar in all domesticated mammals, and therefore called the “domestication syndrome”. Typical symptoms of the domestication syndrome are paedomorphy, changes in colour, endocrinology, physiology, a loss of genetic fitness, reduction in sexual dimorphism and also brain volume. Cattle are a prime example for the domestication syndrome. They are paedomorphic compared to the aurochs, changed in morphology, colouration, body size and show a reduced sexual dimorphism. Whether or not the brain volume also declined during domestication was not tested previously, but is very likely as this has been found in all other domesticated mammal species and cattle show all the other symptoms of the domestication syndrome as well. 

Recently, the brain volume of aurochs has been compared to cattle of multiple breeds using well-preserved skulls. The results have been presented in a paper by Balcarcel et al. 2021. They looked at the brain volume of aurochs and compared them to very derived (dairy and beef) cattle breeds, Chillingham and White park cattle, Lidia (= bullfighting cattle in the paper) and also Heck cattle. 

What they found is that domestic cattle do have smaller brains than the aurochs. Very derived breeds show the greatest reduction in brain size (from 30,6% to 24,9%), Chillingham and White park cattle 18,2% and Lidia only a 15,3% reduction. [1] The authors hypothesize that the less human contact the cattle have the larger is the brain volume. The reduction of brain size of Lidia is considerably lower not only than that of the other cattle breeds but also than that of other domesticated species (f.e. cats 24%, pigs 34%, dogs 29%) [1]. 

This supports my assumption that Lidia, Spanish fighting cattle, are the least derived taurine cattle breed on this world. Heck cattle showed no outstanding pattern in the study [1]. To me this is not surprising considering the breeds it descends from – some of them were derived breeds like Angeln or Murnau-Werdenfelser. 

 

What does this mean for “breeding-back”? For once, it confirms that it would be a waste if Spanish fighting cattle would not play a role in “breeding-back”, considering the obvious value of the breed (go here for my idea in which form the breed could contribute). It would be interesting to know the reduction of brain size of breeds heavily used in “breeding-back” such as Sayaguesa and other Iberian primitive breeds. Perhaps those are similar to Chillingham and White Park cattle. Podolian cattle (including Maremmana and Hungarian grey which are used in “breeding-back”) show a reduction of 21-31%. All in all I do not expect the other “breeding-back” cattle (that means Taurus, Tauros and Auerrind) to have a reduction of brain size as small as Lidia. Perhaps they would be closer to Chillingham cattle or somewhere between Chillingham cattle and more derived breeds, or maybe in the same range as Podolian cattle. It would have to be tested. 

Should brain size become another criterion for “breeding-back”? Well, theoretically, yes, it would be beneficial. But without having Lidia in the mix, which has a drastically smaller reduction of brain size than the other breeds, selection for larger brains would probably not be that fruitful since the difference between the other breeds is not that large. Apart from that, what makes it basically impossible, is the fact that the brain volume cannot be measured in the living animal. Thus, it is not possible to pick a bull with a particularly large brain and use it for breeding, as the large brain can only be diagnosed post mortem. At least I cannot think of a method to measure brain volume in a living cattle individual. 

 

An important question is whether the original brain size of the aurochs is a requirement for living in the wild. I do not think so. While there would certainly be a selective pressure towards larger brains in a cattle population in the wild, it is certainly not a vital requirement for the cattle to have the same encephalization as the aurochs in order to survive. This is proven by the many feral cattle populations on this world, which often descend from usual farm cattle. Furthermore, it is very likely that selection would lead to a secondary enlargement of the brain in a feral cattle population, as the dingo has a larger encephalization than (other) domestic dogs [2]. Thus, it is not really a problem that “breeding-back” cannot actively breed for larger brain size. I am still fond of the idea of practising selection on a neurologic/behavioural level though, by selecting those cattle that exhibit a wildtype-like behaviour (go here for the post). This might perhaps also influence brain size. 

By the way, I am credited for the silhouette of my aurochs cow drawing they use in the paper, which is the first time that my name is mentioned in a peer-reviewed scientific paper. 

Literature 

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

[2] Smith et al.: Brain size/body weight in the dingo (Canis dingo): comparisons with domestic and wild canids. 2018.