As a social animal, there are obviously clear dominance dynamics between horses. However, it isn’t as simple as believing that horses form a hierarchy or ‘pecking order’, and that this supposed ‘hierarchy’ is linear. It is also not as simplistic as to imagine that this social order exists for all situations. Such assumptions arose in human beings because of our complex social organisations that are typically arranged in linear hierarchies such as the military, church, and school. On the contrary

Competition and Dominance Hierarchies in Rats [Silent] (Mowrer, Kornreich, Isabelle Yoffe, 1940)