Since on the average only two of the young survive in the struggle for existence to take the place of their two parents, there is a selection out of the ten million young, none of which are exactly alike, and the selection is determined in nature by the survival of the congenital variety which is fittest to the conditions of life.
But in the struggle for existence it chanced that the early English invaders secured a kingdom, Bernicia, which stretched from the Humber into Lothian, or farther north, as the fortune of battle might at various times determine; and thus, from the centre to the south-east of what is now Scotland, the people had come to be anglicized in speech before the Norman Conquest, though Gaelic survived much later in Galloway.
He considered that a struggle for existence was the inevitable result of the operation of the principle of Malthus in the animal and vegetable worlds.
This struggle for existence has completely changed the habits of some plants, turning the palm and the cactus into climbers, and even some normal species into epiphytes.
Animals and plants as agents of disease or injury form part of the larger subject of the struggle for existence between living organisms, as is recognized even by those who do not so readily apprehend that diseased conditions in general are always signs of defeat in the struggle for existence between the suffering organism and its environment, living and non-living.
In consequence of this excess of births there is a struggle for existence and a survival of the fittest, and consequently an ever-present necessarily acting selection, which either maintains accurately the form of the species from generation to generation or leads to its modification in correspondence with changes in the surrounding circumstances which have relation to its fitness for success in the struggle for life.
A simple illustration will serve to explain these two aspects of mimicry and to show the advantage in the struggle for existence that mimicry confers upon the species concerned.
Von Herder suggested that increase by multiplication with the consequent struggle for existence had played a large part in the organic world, but his theme remained vague and undeveloped.