EVOLUTION. 3-22 EVOLUTION. a relatively indefinite incoherent homogeneity, to a relatively definite coherent heterogeneity, and during which the retained motion (energj ) undergoes a parallel transformation." The es- ce of his view is that there is a continual change in the organic world from the homoge- neous to the heterogeneous, or from the generalized to the specialized. We are also indebted to Spen- cer for the apt expression 'survival of the fittest.' Evolution in general may be divided into (1) inorganic: (2) organic; and (3) mental. Inorganic Evolution. Under this head may be comprised the evolution of the cosmos or male- rial universe; the evolution of our solar system. It is chiefly concerned with the evolution of our own planet, in the manner described by the train- ers of the nebular hypothesis. It involves the gradual development of nlanets from primi- tive nebulous masses through the different gas- eous stages of nebula?, which have been hap- pily called, by Clodd, "the raw material of which suns and systems are formed." Planetary evolution has to take into account the formation of the air or atmosphere, of water, and the origin of the denser minerals comprised in the mass of planets. Chemical evolution then follows. This is the gradual evolution, underlaid and conditioned by the physical forces of matter, from elementary or still simpler conditions, through compounds of various degrees of complexity to the most com- plex of all, i. e. protoplasm. In this substance physico-chemical evolution reached its farthest limits. Since life began inorganic chemistry has gone no further ( Le Conte ) . It is now being recognized that something akin to evolution must have taken place in the elements, since the ele- mentary atoms postulated by the chemist are themselves supposed to be wonderfully complex aggregates of yet smaller particles. Organic Evolution. As we shall see, this is the theory of descent, or an attempt to account for the origin of organic species. The theory of descent, however — of the origin of species — was the result of attempts after the time of Linne to define and classify plants and animals. Owing to the perplexing variations of the living plants and animals, the difficulty of drawing the limits between the more variable species, the multi- plication of specimens in our museums, showing a filiation between many species, though there were wide gaps between others, it became recog- nized by Lamarck that species were artificial, i.e. ideas: that the individual only was natural or existed in nature, and that the plant and the ani- mal kingdoms should be represented by a gene- ical lie., with its stem-forms and later de- rival ives. A- the knowledge of species increased, through the sciences of embryology, morphology, paleon- tology, and the new light thrown on tl artli's history b] greal advances in geology, a sufficient fullness of knowledge resulted, ami alrao I mi .< single year, 1859, the combined researches of the studies of plant ami animal life in different irters of the globe culminated in the epoch- making theory of descent proposed by Darwin, and by Wallace, independently of each other. and seconded by Hooker, Fritz MUller, Asa Gray, 1 1 1 1 v lej . and ot hers. Of Ol "■ El olul 101) we have (lie factoi i i i gem ie bj •■■■ hieh variat ion has brought about, giving us the materials on which natural selection acts. The great facts in nature are adaptation and variation, and the causes of morphogenesis, of the origin of types and species, and all the actions of the physical agents, such as light, heat, cold: the chemical changes of the medium in which plants and ani- mals live; changes in the environment, i.e. cli- mate, temperature, altitude, and physiological changes, such as the use and disuse of org parasitism, and finally heredity. Thc-e are called the 'primary' factors of evolution, while 'natural selection' expresses the results of the action of these primary factors of organic evolution. Mental Evolution. The actions of animals are physiological or reflex, instinctive, and ration- al. Man, with his exalted nervous vigor and brain power, alone thinks, reflects, or is self-conscious. It is probable that the more intelligent insects, and most of the vertebrates, are conscious agents. It is well-nigh impossible in the last analysis to draw the line between the mental acts of animals and man. The germs of reason exist in animals, and the intellectual qualities of man have with little doubt originated from those of the animals, wide as is the gap between the mental, moral, and spiritual nature of num. and the simple, elementary mental faculties of animals. The result of this mental evolution — the physi- cal evidence of which is seen in the great number of vestigial structures handed down from the higher mammals, in the cranial character of the highest existing races as compared with the fos- sil races, in his erect position, his culture-his- tory, with its progressive steps, from primitive savagery up through barbarism to civilization — shows that at first brain use and development, the exercise of wit. cunning, craft, invention, skill, mastery over the elements, over the beasts, over himself: that high endeavor, the gradual elimination of savage impulses, success in the arts and sciences, due to his social mode of life, and finally a tireless devotion in the highest types of the race to the true, the beautiful, and the good, and appreciation of the divine in human nature, and, finally, the practice and exercise of love to God and to man — that all these have been the agents of his mental evolu- tion, of his moral regeneration, and his devotion to his highest ideals, giving him the promise and potency of existence in another world than that witnessing his physical evolution, where his intel- lectual and spiritual forces shall have the freest play, unhampered by a struggle for mere animal existence, by competition with baser forces. Species, Varieties, and Races. The indi- vidual is a concrete fact. A species is an induction, a generalization. (See Classlfica- WON.) Our idea of most species is based on a pair or only a few individuals, whereas tin' actual number of individuals of most species may be counted by the thousands or even mil- lions. Our conception of a species varies with the number of specimens in our collections; and systemal isls naturally differ greatly as to I lie limits of many species. The best definition of spe- eies is thai of Lamarck: "A species is a collec lion of similar individuals which are perpetuated bj generation in the same condition as long as their environmenl has not changed sufficientlj t,, bring about variation in their habits, their character, ami their forms." A variety, or subspecies, is a group of individu
- 1 ls breeding inn to each other, which resemble
