2. Heredity: The variations are inherited directly and improved in succeeding generations.
A long time and favorable conditions are required for the production of new species.
II. Darwin's Theory of Natural Selection.
1. Variations assumed.
2. Heredity: Those slight variations which are of use to the organism will be perpetuated by inheritance.
3. Natural selection is the distinguishing feature of the theory. Through the struggle for existence nature selects those best fitted to survive. The selection of trivial variations that are of advantage to the organism, and their gradual improvement, leads to the production of new species.
III. Weismann's Theory of Continuity of the Germ-plasm.
1. The germ-plasm has had unbroken continuity from the beginning of life. Owing to its impressionable nature, it has an inherited organization of great complexity.
2. Heredity is accounted for on the principle that the offspring is composed of some of the same stuff as its parents. The body-cells are not inherited, i.e.,
3. There is no inheritance of acquired characters.