From these and a multitude of similar cases Kropotkin concludes that while “no naturalist will doubt that the idea of a struggle for life, carried on through organic nature, is the greatest generalization of our century, that struggle is very often collective, against adverse circumstances.” Kropotkin in concluding his consideration of animals, immensely strengthens his position by pointing out various methods by which new species may develop or old ones disappear, without the operation of a deadly competition between individuals. “The squirrels, for instance, when there is a scarcity of cones in the larch forests, remove to the fir-tree forests, and this change of food has certain well known physiological effects on squirrels. If this change of habits does not last--if next year the cones are again plentiful in the dark larch wood--no new variety of squirrels will evidently arise from this cause. But if part of the wide area occupied by the squirrels begins to have its physical characters altered--in consequence of, let us say, a milder climate or desiccation, (drying up) which both bring about an increase of the pine forests in proportion to the larch woods--and if some other conditions occur to induce squirrels to dwell on the outskirts of the desiccating region--we shall then have a new, i. e., an incipient new species of squirrels. A larger proportion of squirrels of the new, better-adapted variety would survive each year, and the intermediate links would die in the course of time, without having been starved out by Malthusian competitors.” Again: “If we take the horses and cattle which are grazing all the winter through in the Steppes of Transbaikalia, we find them very lean and exhausted at the end of the winter. But they grow exhausted not because there is not enough food for all of them--the grass buried under a thin sheet of snow is everywhere in abundance--but because of the difficulty of getting it from beneath the snow and this difficulty is the same for all horses alike. * * * We can safely say that their number are not kept down by competition; that at no time of the year they need struggle, for food and that if they never reach anything, approaching over-population, the cause is in the climate, and not in competition.”