CHAPTER I.

ITS SCOPE AND DEFINITION.

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_A type of evolution_--Development of an egg 3

_Universality of evolution_--Pervades all nature and concerns all departments of thought--One half of all science-- Illustrated (1) by human body, (2) by solar system, (3) by society, (4) by earth, (5) by organic kingdom--The term evolution usually, but not rightly, confined to this last 3

_Definition of evolution_--_I. Progressive change_--Shown in the animal body, or the _Ontogenic_ series--In the animal scale, or the _Taxonomic_ series--In the geological, or _Phylogenic_ series--The three series similar, though not identical 8

_II. Change according to certain laws_--Three laws of succession of organic forms 11

(_a_) _Law of differentiation_--Early forms are generalized; afterwards separated into specialized forms--Illustrated by fishes, by birds--Whole process of differentiation illustrated by growth and branching of a tree 11

(_b_) _Law of progress of the whole_--Mistake of confounding evolution with upward progress--How far true, and how far false--Illustrated by branching tree--Examples of this mistake in the popular mind--In the scientific mind 13

(_c_) _Law of cyclical movement_--Shown in geological history-- Age of mollusks, fishes, reptiles, mammals, man--Illustrated again by a branching tree--Increasing complexity as well as height--Illustrated by diagram 16

_The above three laws are laws of evolution_--_Differentiation_ --Shown in the development of an egg, the type of evolution 19

_Progress of the whole_--Not progress of all parts--Shown in the development of an egg 22

_Cyclical movement_--Less fundamental than other two--Shown in Ontogeny of body, of mind--Increasing complexity--Necessity of continued advance--Otherwise deterioration--All these laws shown in progress of society---Differentiation shown-- Progress of the whole but not of all parts shown--Cyclical movement shown--In social evolution, however, there is another element, viz., conscious voluntary progress---This kind of evolution contrasted with the other 22

_III. Change by means of resident forces_--This is the point of dispute--Sense in which we use term resident forces--Does not touch question of origin of natural forces 27

_The two views of the origin of organic forms briefly contrasted_ --As to whether natural or supernatural--As to variability, definite or indefinite--As to change from one species to another by transmutation or substitution--As to universality of law of continuity 29