I recently heard about a clinic (Natural Horsemanship type of thing) in my area, where they turned a group of horses loose in the arena to let the participants observe 'natural' horse behaviour. This could be massively misleading and, I think, damaging to our view of horses. The behaviours you see might be in the horse's repertoire, but it is highly unlikely to be their 'normal' behaviour - when you put them into such an abnormal situation, you can't expect normal responses. The level of unfriendly interactions between this group of horses could (and I'm not saying it was, I wasn't there) then be used to justify us behaving in a confrontational way with our horses - its 'what they understand'.
This morning, I read a great article in the Journal of the Equine Behaviour Forum by Lucy Rees, 'Why Study Feral Horse Ethology'. Ethology, she explains, is the science of animal behaviour. She talks of students she has taken on field study trips and says 'Watching normal horse behaviour makes them realize that they have never seen normal horses, for it is only when you see what normal is that you identify what is abnormal. Looking at social relations of domestic horses is about as useful as studying family relationships in a prison.'
She continues 'What we fail to realise is that even domestic horses kept in little, stable groups in fields - the best conditions we can offer - are considerably more aggressive to each other than are feral horses. One of the greatest impacts of feral horse behaviour is their peacefulness. They do not argue or give each other orders, but get on with staying alive together'
We do not have all the answers as to why domestic horses are more aggressive, but Lucy Rees puts forward several sensible possibilities - competition over food, overcrowding, boredom, poor socialisation to name a few.
For myself, I wouldn't discount the usefulness of looking at social relations of domestic horses - we need to understand the behaviour of domesticated horses - I watch mine all the time, and their social interactions play a significant role in how I manage them, for example, as well as helping me understand the individuals and how to interact with them. But we shouldn't confuse this with observing 'natural' horse behaviour!