Purer than thou

wisent in mountains

You might have seen articles lately (for example here and here) announcing the return of the European bison (Bison bonasus), a seeming success story for the rewilding movement in Europe. Surely, it is a great thing to have an animal come back from the brink! However, what is less talked about, and what I want to discuss in this post, is what exactly is coming back. In the background of the recent expansion of the species, there is a quiet battle for purity, one which I find to be both interesting in and of itself, and quite important for the future of conservation.

The biggest land mammal in Europe is the Wisent, also known as the European Bison. Like other magnificent European things, it was almost driven off the cliff by WWI, and then edged close yet again by WWII. Before the two great wars of the 20th century, the wisent population was far from healthy: it had survived thanks to its magnificence being desirable for aristocratic types. In practice, it had been the property of kings and had survived into the 20th century thanks to that royal ‘protection’. So war, administrative and legal regimes, and the power of the aristocracy, became the most important factors affecting the wisent’s fate, both in terms of its demise and its eventual comeback. In this sense at least, it can be said that the wisent has been a citizen of sorts for quite some time.

The Białowieża forest, in Poland, was the last place on the continent where free-roaming wisent lived. They survived there until 1919 when, at the end of the war, the last specimens had been hunted by starving locals. It is interesting to note that, in recounting this history, the editors of the European Bison Pedigree Book (EBPB), basically the bible for wisent conservation, characterize the hunting of the last remaining animals in the forest as poaching. I wonder what the take-away point of using this term is: if we are committed to bison conservation, we must, as it were out of moral duty, insist on the act of feeding oneself when hungry being despicable? However that may be, it remains the case that the bison of the Białowieża were gone. The other free roaming population in Europe was in the Western Caucasus mountains, and were considered as a separate sub-species, known as mountain bison. They disappeared in 1927.

The disappearance of the Polish wisent prompted the formation of a society for its conservation, the International Society for the Protection of the European Bison, started in 1923 in Berlin. In 1924 it counted 66 bison left, but without yet knowing which of those would turn out to be ‘true’ wisent. After weeding out the individuals whose pedigree could not be vouched for, the Society established that there were 55 pure wisent left in the world. Of those, only 12 managed to provide genetic material to present generations. These ‘founding members’, as they are called, are listed in the EBPB, the document that has acted, since the beginning of bison conservation, as the standard for judging whether an animal is or is not a wisent at all.

The original surviving animals are not only called founders, recalling the name usually given to those that put the bases of nations, but they also all have individual names. Reading through the history of the wisent, one starts feeling sad at the slow disappearance of the founders. So we learn that the cow F 89 BILMA, though one of the original 55, failed to have any offspring, and therefore sadly remains a mere photograph. On the other hand M 100 KAUKASUS is singlehandedly responsible for an entire sub-line of wisent, namely the Lowland-Caucasian line. Recall that a sub-population of wisent survived in the Caucasus mountains until 1927. Of that particular bloodline, only one specimen survived in captivity: mr. Kaukasus. Because of his survival, the EBPB decided to run two separate lines of bison pedigree: the Lowland line, which includes only bison from the Białowieża, and the Lowland-Caucasian line, which includes mr. Kaukasus as a founder. So any bison alive today that can trace their ancestry to that one surviving bull is, for that reason, part of a separate line of bison, the Lowland-Caucasian.

The first edition of the EBPB came out in 1932 and numbered 177 animals. Since then, the wisent has had a continuous increase, reaching around 4000 individuals today (estimates vary between 3 and 5000). However, this counts only animals whose genetic purity can be proved and which can therefore be included in the EBPB. It could be reasonably asked why such proof is needed. It seems to me that the inherent goodness of genetic purity goes unquestioned; it is simply taken to be so. Here is a telling quote from the editors of the EBPB: “many breeders had played with hybridization between European and American bison, an easy enough feat to accomplish, as it turned out, and a “dangerous” one, since the hybrids are fertile from the first generation, and can also breed successfully with the original species. Hybrids of this kind, and back-crosses with a significant amount of wisent blood in particular, look so similar to true, pure-blood European bison that there is no effective way to tell them apart” (full document available here). So the problem is not the fitness of the animals – quite the contrary, given the extreme genetic bottleneck that the species passed through, purity might be a fitness problem. Instead, the problem seems to be that there is no way of discerning between true and fake wisent, the fake being defined as anything that is not entirely pure.

In the Western Caucasus mountains there remains the largest truly free-roaming herd of wisent in Europe. Until not long ago, before being once again decimated by hunters, it numbered around 1000 individuals. However, these mountain bison are not recognized by the EBPB, and therefore do not count as true wisent, because they have some American bison blood mixed in. The ‘some’ amounts to about 5%, but as explained earlier, any amount is enough for disqualification. This stance is all the more surprising given that the supposedly fake bison are the only herd in Europe that is entirely self-sustaining. Even the Białowieża group, the pride of wisent conservation, is routinely fed in the winter. And though the popular articles praising the reintroduction of bison fail to dwell on the point, it is the case that wherever ‘pure’ wisent have been introduced, they have had to be fed, while some died from disease (a problem in a genetically homogenous population) or predation (the latest, by feral dogs; see this story). And importantly, the pure bison that need constant human attention to survive have very little idea about being ‘wild’, and little chance to remake a wild bison culture, seeing how they need our attention. Coming from zoos and breeding programs spread throughout the continent, in different environments and under different conditions, reintroduced individuals are, until now, far from forming independent herds. On the strength of the Western Caucasian example, it makes one wonder whether a little impurity wouldn’t help.

The idea that somehow the genetic purity of the wisent is more important that anything, including their viability as free herds, needs some explaining. On the strength of the facts, it is far from obvious. So far, it has been the opposite position that has been better defended. In a recent paper (available here), Rohwer and Marris argue that we have no prima facie duty to preserve so-called genetic integrity. Tellingly, they use the American bison as a case – there, the idea that somehow impurity is a problem has had a very similar history. Their argument goes through all the various reasons conservationists might advance for the primacy of genetic integrity, and finds them wanting. At the most, we might have a derivative duty, they conclude, to protect something life genetic integrity. In Europe, the idea of purity is also easily tied to the nationalism that has plagued the continent for centuries. The EBPB does not fail to notice that the comeback of the wisent coincided with the resurgence of Poland as a nation. And the Białowieża herd is taken to be the unquestioned model of wisent conservation, despite the regular feeding it requires. Why, one wonders, if not for some ideological idea of purity mixed in with nationalist fervor, would this be the case?

As the EBPB itself recognizes, in the quote above, hybridization is a danger precisely because it might be too successful. For a species that is so genetically impoverished, it seems to me that we need much better arguments to keep it that way than appeals to the supposedly obvious advantage of being pure. The myth of purity is not a biological idea, but itself a hybrid with dangerous pedigree and little to recommend it for the future of conservation.


  1. Another fascinating blog and reminiscent of the story of the Red Kite (Milvus milvus) UK which went through a similarly savage genetic bottleneck between the late 1890s and the mid-1970s with all the birds descended from a single surviving ♀ in Wales IIRR until a second ♀ joined the population, probably from Germany, around 1973. (This is known by DNA work on illegal egg collections and carcasses of poisoned kites). Recovery with absolute protection was painfully slow with poor production of young until 1989 when it was decided to release young Spanish birds to improve the genetic profile of the population. They have boomed. There are now well over a thousand pairs breeding and single roosts of more than 1000 birds at some sites. You can see dozens in a day along the Chilterns NW of London.


    I guess the view about purity of Wisent can in some senses be defended in that should the pure European animals descend into an extinction spiral (as seems likely, eventually) then the Caucasus herds could be used to plump them up rather as the Spanish birds saved the Red Kite in UK.


  2. Thanks a lot for this Paul. Indeed, I think there are many parallels – the idea of purity in itself being worthwhile saving runs quite deep in the conservation ethos. As far as the wisent, it will indeed be interesting to see whether ‘pure’ populations will suffer in the long run to the point of having to hybridise them. By that point though, the ones in the Caucasus might be gone, due to hunting. There will probably be the American ones though. Interestingly, the majority of those have been shown to carry cattle DNA…


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