Within the group, an order of dominance is established with the most dominant individual taking the leadership. The order then progresses downward to the lowest ranking and most submissive individual in the group. Within the group there is a constant vieing and jockeying for position and this can become quite competitive at the upper levels. In range herds of domestic horses, the leadership is sometimes assumed by a gelding, suggesting that not gender, but seniority is the reason wild horses are led by a mare. In nature, old stallions are soon displaced by a younger stallion and go off to live in bachelor bands.
Nature demands that the youngest and the fittest stallions sire the next generation.
Animals, like dogs, horses and humans, which live in groups, have two characteristics which are of significance to us. First of all, they crave acceptance by the group. Praise, therefore, is a reward to such creatures and is an effective training tool. If you call your dog, for example, and praise him for obeying, an expression of joy usually results. That's why we humans can become so deeply attached to our animals.