I. The success with which selection has been applied by man in making his breeds of domestic animals and plants: and this even in ancient times when the selection was unconscious, viz. when breeding was not thought of, but the most useful animals and plants were kept and the others destroyed. “Selection acts only by the accumulation of very slight or greater variations,” and man in thus accumulating “_may be said_ to make the wool of one sheep good for carpets, and another for cloth, &c.” II. Slight variations of all parts of the organism occur in nature, and if a being could select with reference to the whole structure, what changes might he not effect in the almost unlimited time of which geology assures us. III. Animals increase so fast that, but for extermination, the earth would not hold the progeny of even the slowest breeding animal. Only a few in each generation can live; hence the struggle for life, which has never yet been sufficiently appreciated. “What a trifling difference must often determine which shall survive and which perish!” Thus is supplied the “unerring power” of “_Natural Selection_ ... which selects exclusively for the good of each organic being.” IV. If a country were changing the altered conditions would tend to cause variation, “not but what I believe most beings vary at all times enough for selection to act on.” Extermination would expose the remainder to “the mutual action of a different set of inhabitants, which I believe to be more important to the life of each being than mere climate.” In the infinite complexity of the struggle for life “I cannot doubt that during millions of generations individuals of a species will be born with some slight variation profitable to some part of its economy; such will have a better chance of surviving and propagating this variation, which again will be slowly increased by the accumulative action of natural selection; and the variety thus formed will either coexist with, or more commonly will exterminate its parent form.” Thus complex adaptations like those of woodpecker or mistletoe may be produced. V. Numerous difficulties can be answered satisfactorily in time. The supposed changes are only very gradual, and very slow, “only a few undergoing change at any one time.” The imperfection of the geological record accounts for deficient direct evidence of change.