When a number of animals live in a group, herd or flock, they carry on the struggle for existence in common against the outside world … The animals which live socially no longer wage a struggle against each other, wherein the weak succumb; just the reverse, the weak enjoy the same advantages as the strong. When some animals have the advantage by means of greater strength, sharper smell, or experience in finding the best pasture or in warding off the enemy, this advantage does not accrue only to these better fitted, but also to the entire group. This combining of the animals’ separate powers into one unit gives to the group a new and much stronger power than any one individual possessed, even the strongest. It is owing to this united strength that the defenseless plant-eaters can ward off rapacious animals. It is only by means of this unity that some animals are able to protect their young.