What makes breeding-back so fascinating?

I have always been fascinated with extinct animals, among dinosaurs especially those that have been exterminated by man. The thylacine was the hero of my early childhood. When I rediscovered this subject for me some years ago, and researched on all the exterminated megafauna around the globe, I inevitably concerned myself with the aurochs and heard of those “breeding-back” attempts. The idea fascinated me – selective breeding with living descendants in order to reconstruct the original wild type and to fill a gap in nature man created. I became almost obsessed with this idea, so that I always feel I have to explain myself why I engage myself with the horn shapes of some cows or the coat colour of some horses. It is true that the whole breeding-back issue is a very narrow niche, but to me it is connected to a lot of other fields.

Arguing about the need of reintroducing aurochs-like cattle and primitive horses into their former range partly depends on the so-called megaherbivore hypothesis which claims large herbivores through their interaction with the flora more diverse landscapes than a closed canopy forest or climax biotope would be. I am no hardliner of that thesis (some of them suggest that Europe would be an open savannah/grassland with huge herds of herbivores like the African Serengeti) but I think large herbivores do have an influence on the flora they live in, though certainly not a larger one than climate, soil parameters and terrain. There is a lot of literature on this subject to dig in, and it is exciting for me to try to compose a synthesis of that highly polarized discussion. The megaherbivore hypothesis itself is connected with the Overkill hypothesis that suggests that many members of the megafauna that died out towards the end of the last glacial period or shortly after it are victims of early human hunters. As the theory outlined above, this is another very controversial and emotionalized subject – I had been concerning myself with this issue years before I discovered breeding-back for me, but I won’t discuss it here any further because it is not really relevant for breeding-back.

I always want to emphasize that breeding-back is not simply something for fanciers that want to create the breed of their dreams and keep them on paddock is or in zoos, but that it is the long-term goal to create an authentic, ecologic substitute for the extinct archetypes they are bred to resemble. These animals even now have a practical use in conservation and demonstrate their importance in their former ecosystems; regardless of how large the impact of megaherbivores on landscapes really is, they were and are important for a lot of species in their native biotopes. Many grazing projects in Germany, the Netherlands and other countries underline that. 

© Jeroen Helmer

Reintroduction of large herbivores also provide empirical tests for hypotheses like the megaherbivore hypothesis or the cascade caused by the lack of predators which leads to a high population density of herbivores and therefore overgrazing, and what that means for the interaction between herbivores and the biodiversity of flora and fauna. Breeding-back is a tool of conservation because releasing their results into their native habitats is the reintroduction of a native species. That is why large reintroduction initiatives like Rewilding Europe have integrated primitive cattle and horses into their programmes. Europe’s megafauna without wild cattle and horses as much as Southern Africa without populations of the Plain’s zebra simply would not be complete, and breeding-back gives us the chance to fill that gap in the most satisfying way.

The breeding process itself requires to have some knowledge on the rules of inheritance and its relevance for breeding a certain desired phenotype. Inevitably you get into colour genetics. I also try to find out more about the difference of qualitative and quantitative features and how to select efficiently on the latter traits. Furthermore, population genetics are relevant for breeding-back. If you finally have a herd (or several herds) of animals with the desired features and start to expand and fragment the population the genetic composition of the new sub-populations gets changed, and some will have a higher portion of undesired recessive alleles or variations of any trait than others, leading to phenotypic more or less diverging herds (genetic drift). Genetics also are the tool to determinate whether there was local introgression from aurochs or wild horses into their respective domestic counterparts and how extensive that introgression was. It also explains why selective breeding just with related animals that do neither descend from the desired extinct animal nor contain all the genes in the extinct gene pool will only produce a superficial similarity. I’m an amateur on genetics but breeding-back certainly increased my knowledge a lot.

Breeding-back is closely connected with dedomestication. To me, dedomestication is exciting because it actually is evolution happening in front of our eyes – yet feral animals are sadly often considered ecological pests and invasive species by the majority of biologists (in many ecosystems they certainly are, though) and are under-studied. Of course the environment influences the condition of the body of the animals, but the changes observed in domestic animals becoming feral are certainly also genetic, and in many cases “new old traits” evolve, phenotypic as much as behavioural. The pleiotrophic effects involved in dedomestication surprisingly favours features not intuitively thought to be influenced by natural/sexual selection after only a few generations in the wild; this is exactly the reversal of what has been observed in the Farm fox experiment, which aims to study the genetic, phenotypic and behavioural changes caused by domestication. 

Feral hogs in Alabama

In fact, breeding-back also requires to research on the changes that wild animals go through while being domesticated to better understand how a non-dedomesticated breeding-back result will be different from the desired extinct wild type. Feral cattle and horses are prime models for filling gaps in our knowledge about the social behaviour and ecology of their wild types, so that there is a mutual gain of information: the desired archetype tells us what breeding-back has to focus on, and results of breeding-back living semi-feral or feral tell us some aspects about the extinct archetypes we otherwise could never know from the limited data we have.

Furthermore, breeding-back is also an exciting historical, archaeological and paleontological puzzle, because doing that work efficiently requires a profound knowledge on the extinct animals you are focusing on. What did it look like exactly? What do we know about its behaviour and its ecologic niche? What was its preferred habitat and its influence on other faunal and floral species? How large was its total range in a climatically comparable period? What were the causes of its extinction and the chronology of this process? In order to answer these questions information obtained from the sources mentioned above have to be put together properly, and you have to know where to look for and which sources are trustable and which are not. Many historic references are reproduced only from second or third hand, leading to confusions and Chinese whispers. The more information you have, the more complete the picture will get. You constantly have to reconsider the conclusions you have drawn previously, often leading to surprises, and pay attention that your view does not turn into a static thought system and biased view – this would be exactly the opposite of scientific thinking, and unfortunately sometimes is practised by exactly those who claim to have the only scientific approach.

Researching on other wild bovines brings you information about the aurochs and vice versa

The species that are the goal of breeding-back projects also can serve as models for their taxonomic group. The Aurochs, Quagga and Tarpan engage me to concern myself with bovine and equine evolution and phylogeny, and researching on related species is always very helpful as it might have some implication for reconstructing the biology of their extinct relatives. The basic anatomy, digestion systems etc. are roughly the same among perissodactyls and ruminants, so if you learn about the physiology of cattle and horses you learn about the physiology of a whole set of species. Furthermore, it is interesting to compare the social behaviour of the different species. For example, that of each of the wild bovines (buffaloes excluded) is about the same. What is the purpose of the exceptional sexual dichromatism displayed by some bovids, which is rather unusual among mammals? Why do horses and bison not show it? Therefore, researching on the biology of these very few species gives a clue on the biology of a lot of mammals in general.

Reconstructing an aurochs cow (Sassenberg specimen).  All rights reserved.

For me as a self-thought amateur animal artist, the obsession of drawing the one accurate and satisfying reconstruction of whatever species relevant for breeding-back is very helpful for improving my artistic skills. As I drew extinct dinosaurs and other Mesozoic reptiles for many years, I was quite inexperienced when I started drawing exterminated mammals.  Not only did drawing loads of aurochs increase my knowledge on mammalian soft-tissue anatomy a lot, it also is incredibly refreshing to shift from dinosaurs to herbivorous mammals. But art is not only relevant for me. Qualitative, artistic reconstructions are important for breeding back because it shows what the breeding has to focus on, and how the animals have to look like to be satisfying. If you don’t know the appearance of the desired end result, you cannot select for it.

As you see, breeding-back motivates you to dig into a diverse set of subjects and always remains interesting and versatile.