Back in my teenage years, I was very much into Mesozoic dinosaurs. It changed in my late teens and shifted towards recently extinct animals, especially ungulates, because these animals are much closer to our time and thus more graspable. My enthusiasm for aurochs was partly always fueled by the thought that, because of its very recent extinction, it might one day come back with new technology. But will that ever happen?
In the past, I made posts on why the aurochs would be the prime candidate for “de-extinction”. You can go here, for example. Having had a deeper look into the genetic framework around CRISPR-Cas9 and what would be necessary for a successful “de-extinction” of the aurochs, I changed my mind fundamentally. The aurochs might actually be a very tricky case, if not technically impossible. Let’s have a look at why that might be the case step by step:
1. The reconstructed genome is not the original genome
Ancient DNA does not come as a nice, complete DNA strand, but as isolated fragments that are used to try to infer the original genome. Many pieces cover duplications of sequences. For the reconstruction, you need a template, a close relative that is used for puzzling the pieces together. In the case of the aurochs genomes, domestic cattle and related wild bovines are used as a template. The problem: structural variations, such as duplications of genes (that can have a huge impact on the organism), have a high risk of staying undetected in this method. For example, if the aurochs had an additional copy of a gene of the FGF family, or at least an additional enhancer, it would explain why aurochs were taller, larger, had more developed horns, and such a robust skull; yet, the duplication would stay undetected because the template (the genome of the related species) does not have it. Thus, even if scientists manage to create a bovine that has 100% of the reconstructed aurochs genome, there is the risk that this reconstruction is different from the original genome, with those differences having a large impact on the development of the animal – maybe even lethality.
2. Creating a bovine with 100% of the reconstructed genome is technically basically impossible
Domestication changed the hormonal and developmental system of cattle dramatically, with the morphological changes being a consequence of that. Not only were probably hundreds or even thousands of genes determining the hormonal and developmental regime of the animals affected by domestication, but also the accompanying regulatory sequences and epigenetic programs. So if we were to change a cattle genome into a (reconstructed) aurochs genome, we are probably talking about hundreds or thousands of edits, with a technique that only allows one change at a time and might also produce errors. It is highly impracticable.
3. Even exchanging a few important alleles would be problematic
Many of the changes during domestication did probably not change the proteins produced by the genes directly, but when, where and how long the genes are expressed. The typical domestic paedomorphy is basically a prolonged juvenile gene expression. “Removing” paedomorphy would make the bovines already a lot more aurochs-like. But developmental genes are part of a highly nuanced system with complex interactions between the individual genes, and changing a few “key genes” can lead to wrong expressions, distorted development or even lethality. And even in more discrete traits, such as horn shape, even if we identify a gene that regulates the classic aurochs horn shape and we were to insert the allele into a cattle genome, there is no guarantee the allele would work the way it would work in an aurochs, because the genetic, epigenetic and developmental environment is different. It would have to be executed by “trial and error”, which would require a large number of cattle individuals and many breeding generations. And if the inserted aurochs allele is to work in a proper, aurochs-like fashion, it would require the developmental program of an aurochs and not of domestic cattle, which brings us to the problem illustrated in point 2 again. Just inserting an aurochs allele into a domestic developmental framework might lead to distorted development and traits that are nothing like an aurochs’ at all.
4. In the same time span and at much lower cost, good “breeding-back” cattle could be released into a suitable reserve and natural selection does the rest
Implanting a few “key” alleles from ancient DNA into “breeding-back” cattle would require research on which alleles are to be inserted and a lot of trial and error to not disrupt the animal’s development, and it would probably work only with one allele per generation. Considering this, breeding for a more aurochs-like phenotype might actually have been the more efficient way all along. It selects for aurochs-like traits without disrupting the developmental pathways – surely, it takes long, but so would genome editing. And both strategies will not result in an original aurochs.
Therefore, my take on the subject currently is take the best “breeding-back” cattle, release them in a suitable area and let natural selection do the rest. According to my “dedomestication hypothesis”, that I am sure many of my readers are familiar with, wildtype traits (be it morphological, ethological, hormonal/developmental) will have a selective advantage over the domestic counterparts and the cattle will become continuously more wildtype-like with time. The cost of letting natural selection do the rest is virtually zero compared to highly effortful genome editing, which has no guarantee that it will work as planned. Therefore, I think that before we try to create an “aurochsified” cattle in the lab, we should concentrate our resources on finding or creating an area where a large-enough population of “breeding-back” cattle can live under natural circumstances, ideally with natural and sexual selection, and also pressure from predators.
5. Are modern breeding-back cattle “ready to be released”?
This brings us to the next question, namely if modern “breeding-back” cattle are already suited for such an endeavour. My answer is a clear and strong yes. I think that modern “breeding-back” is very close to the pinnacle of what can be achieved with domestic cattle, apart from the fact that they are still very heterogeneous. But stabilizing the phenotype might actually take centuries, considering the large number of genes involved and the slow reproduction of cattle. From the ecological standpoint, I think the cattle are very fit – cattle tend to feralize rather easy, and so should “breeding-back” cattle, which descend from hardy and robust landraces. Of course, the currently running projects can still strive for even better animals, but I am very satisfied with the current results. I think it is time to look for an area large enough and isolated from humans enough so that the cattle can develop freely and unhindered from any human interference – at the same time, it would be very interesting to document phenotypic changes of these released cattle over decades in a long-term study.
6. Conclusion: Will the aurochs ever come back?
If you strictly mean the original animal in all aspects like it was 100.000, 10.000 or 1000 years ago, we can effectively almost rule that out with certainty. No matter which route we take, there will be genetic and phenotypic differences. But in a more sensu lato way of the term, we can produce a type of bovine that is barely distinguishable from the aurochs (apart from vestiges of domestication that will appear in several individuals for a very long time, such as small white spots, recessive diluted coat colours etc.) that also functions ecologically the same way, shows the same social behaviour patterns (as all domestic cattle do) and is also at least partly shaped by natural selection, by taking the best of the best of “breeding-back” cattle and releasing them into a suitable area.
