As a general rule of biology, migratory species are less 'aggressive' than sedentary ones. There is one obvious reason why this should be so. The migration itself, like the pilgrimage, is the hard journey: a 'leveller' on which the 'fit' survive and stragglers fall by the wayside. The journey thus pre-empts the need for hierarchies and shows of dominance. The 'dictators' of the animal kingdom are those who live in an ambience of plenty. The anarchists, as always, are the 'gentlemen of the road'.