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Show 6 JNTRODUCTION. conditions of which we have abundant geological evidence, or from any 'other cause; if, in the long course of ages, inheritable variations ever arise in any way advantageous to any being under its excessively compl ex ~ncl cban~ing r~la~ions ?f life ; and it would be a strange fact 1f benefiCial vanatwns d1d never arise, seeing how many have arisen which man has taken advantage of for his own profit or pleasure ; if then these contingencies ever occur, and I do not see how the probability of their occurrence can be doubted, then the severe and oftenrecurrent struggle for existence will determine that those variations, however slight, which are favonrable shall be preserved or selected, and those which are unfavourable shall be destroyed. This preservation, during the battle for life, of varieties which po. sess any ad vantnge in structure, constitution, or instinct, I have called N atnral Selection; and Mr. Herbert Spencer has well ex pres ed the same idea by the Sur vi val of the Fittest. The term "natnral selection" is in some respects a bad one, as it seems to imply conscious choice; but this will be disregarded after a little familiarity. No one objects to chemist speaking of " elective affinity;" and certainly an acid bas no more choice in combining with a base, than the conditions of life have in determining whether or not a new form be selected or preserved. The term is so far a good one as it brings into connection the production of domestic races by man's power of selection, and the natural preservation of varieties and species in a state of nature. For brevity sake I sometimes speak of natural selection as an intelligent power ;-in the same way as astronomers speak of the attraction of gravity as ruling the movements of the planets, or as agriculturists speak of man making domestic races by his power of selection. In the one case, as in tho other, selection docs nothing without variability, and this depends in some manner on the action of the surrounding circumstances on the organi m. I have, also, often personified the word Nature; for I have found it difficult to avoid this ambiguity; but I mean by nature only the aggregate action and product of many naturallaws,-and by laws only the ascertained sequence of events. NATURAL SELECTION. 7 In the chapter devoted to natural selection I shall show from experiment and from a multitude of facts, that the greatest amount of life can be supported on each spot by gr at diversification or divergence in the structure and constitution of its inhabitants. \Ve shall, also, see that the continued production of new forms through natural selection, which implies that each new variety has some advantage over others, almost inevitauly leads to the extermination of the older and less improved forms. These latter are almost necessarily intermediate in structure as well as in descent between the last- produced forms and their original parent- species. Now, if we suppose a species to produce two or more varieties, and these in the course of time to produce other varieties, the principle ·of good being derived from diversification of structure will generally lead to the preservation of the most divergent varieties ; thus the lesser differences characteri tic of varieties come to be augmented into the greater differences characteristic of species, and, by the extermination of the older intermediate forms, new species come to be distinctly defin ed objects. Thus, also, we shall see how it is that organic beings can be classed by what is called a natural method in distinct groups- species under genera, and genera under families. As all the inhabitants of each country may be said, owing to their high rate of reproduction, to be striving to increaRe in numbers; as each form is related to many other forms in the struggle for life,-for destroy any one and its place will be seized by others; as every part of the organization occasionally varies in· some slight degree, and as natural selection acts exclusively by the preservation of variations which are advantageous under the excessively complex conditions to which each being is exposed, no limit exists to the number, singularity, and perfection of the contrivances and co-adaptations which may thus be produced. An anitnal or a plant may thus slowly become related in its structure and habits in the mo8t intricate manner to many other animals and plants, and to the physical conditions of its home. Variations in the organization will in some cases be aided by habit, or by the use anrl. disuse of parts, and they will be governed by the direct action |