Behaviour selection - a new perspective for "breeding-back"?

Most „breeding-back“ projects do select on behaviour in some way. Individuals that are too aggressive, or too nervous and explosively behaving, are getting culled in all projects because they are too difficult and dangerous to work with. A question that came up in my mind while researching on the connections between behaviour and morphology is if a project that selects on wildtype-like behaviour would be capable of reversing some typically domestic changes in morphology and other aspects that traditional breeding-back cannot. 

Behaviour is interconnected with a number of other organismic traits as outlined in a number of posts (go here), what also shows in a connection between tame behaviour and morphological changes associated with domestication (see the Farm fox experiment). Selection exclusively on tameness produces most of the typical symptoms of the domestication syndrome, f.e. reduced brain volume, neoteny, piebald colour and other morphological changes because of developmental cascades and pleiotropic effects. So tame and neotenic behaviour goes hand in hand with a domestic morphology. Domestic cattle have been selected on docility and agreeableness for millennia. The Iberian fighting bull (Lidia), on the other hand, is the cattle breed that has the most aurochs-like (or: least derived) morphology, and is also the least tame breed as it was selected on agility and aggression and not tame and agreeable behaviour. This of course provokes the question whether this is a coincidence or not; did the Spanish fighting bull keep its aurochs-like morphology because it was never selected on tameness, but on aggression instead? This has been outlined in the post The looks vs. behaviour problem and the Spanish fighting bull (the fact that Lidia are allowed to fight for mating rights alone cannot explain their aurochs-like morphology, as this is also true for other breeds that do not have an aurochs-like morphology such as Eringer or Chillingham cattle).  

And an even more interesting question: would domestic cattle that are selected on wildtype behaviour traits (important: not necessarily aggression) also redevelop an aurochs-like morphology? 

The latter question could be highly relevant. While modern breeding-back has produced a number of very beautiful results with good horns, size and colour, none of them has a morphology as aurochs-like as in good Lidia bulls, and have a morphology and skull shape that reveals they are domestic cattle. If selection on wildtype behaviour could indeed reverse the processes and cascades that develop the domestic morphology we see and perhaps even more, the results could be more aurochs-like than anything else after a sufficient amount of time. A project selecting aurochs-like cattle for wildtype behaviour might be worth a try. 

It is important to note that cattle behaviour towards humans also depends a lot on socialization and not only genetics. If raised under natural circumstances and treated the same, you could probably also fight with a Holstein bull, while you could probably also milk a Lidia cow if raised in a barn with a lot of human contact. But there are genetic differences regarding the potential behaviour spectrum the cattle will show. For example, Lidia has of course a much more extreme fight/flight reaction than Highland cattle, and most if not all cattle will be in between. 

Crossbred populations of course show a mosaic of possible behaviours, and so do “breeding-back” herds. For example, individuals of breed combinations without any Lidia in the mix showed the same nervous behaviour as most of the Lidia crosses, while some Lidia crosses were as relaxed as non-Lidia individuals. As all of them are raised in the same population under the same circumstances, the chance is high that this has a genetic background. But not only the behaviour towards humans when being handled or flight distance is relevant, but the whole behavioural spectrum. Heck cattle, being a mix of derived and less-derived cattle breeds, is also heterogeneous on behaviour aspects such as calving. While most Heck cows calve outside the herd near a shelter as most bovid species do, some calve in the herd, which is a domestic condition. 

Selection on wildtype behaviour

By selection on wildtype behaviour I do not mean aggression/nervousness, and not the behaviour towards humans alone, but the whole set of behavioural nuances. This would include flight distance (we do not know what the flight distance of wild aurochs was, but you probably would not have been able to approach and stroke them), stress response, agility, awareness (not nervousness), calving in a shelter, herding behaviour, and other aspects. Individuals that are too tame could be selected out, as well as cows that calve in midst of the herd or do not show herding behaviour. Stress response and agility could be tested in a manner similar to how it is tested in Lidia cattle, where riders ride in the herd and tease the individuals with sticks. Not that the most aggressive individuals would be favoured, but rather those that behave and move apathetic would be selected out. 

Selection on stress response, awareness and agility would certainly influence the production of corticosteroids and perhaps even thyroid hormones, what itself would probably influence the development and morphology of the animals. It could be seen as a true reversal of the selective pressure that led to domestication, as selection on tameness affected the production of exactly these hormones, what probably also caused the typical domestic morphology. 

The question is which cattle to take for such a project. I would select good individuals of breeding-back projects in order to achieve a basic similarity with the aurochs right from the beginning, and because they are mixed populations and thus have a wider spectrum of different behaviours than purebred herds. 

How to handle these cattle 

For such a project it would probably not be possible to handle the cattle the way they are handled in grazing projects. As I wrote above, many cattle in grazing projects are slaughtered because they are too difficult to handle and a project selecting on wildtype behaviour would probably produce a lot of such. It would be best to keep the cattle the way Lidia or bison are kept, also concerning the equipment. In the end, a wild aurochs would also be much more difficult to handle than domestic cattle (and even the best breeding back cattle are still domestic cattle). Also, it probably has a reason why most grazing projects use cattle and not wisents. 

The perspective 

The goal of the project would be to see if a selection on wildtype behaviour would indeed also lead to a more wildtype-like morphology due to the hormonal and developmental cascades that caused them in the first place when cattle were domesticated. It would, basically, be the reverse to the famous Farm fox project and with another species. Probably the cattle would be more active and agile, and if their body changes they might indeed develop longer legs plus a slenderer, more athletic and muscular body. Perhaps even other effects of domestication such as paedomorphy, which influence the skull shape and horn growth, might become reduced. 

It is just an idea, but in my opinion an idea that is really worth testing.