Mr.
Darwin alleges four or five primal forms, acknowledging that analogy would lead him up to one.

But other members of this school consistently and boldly follow up the stream to its fountain, and allege a single primeval living seed as the origin of all living things, and that this must have been a microscopic animalcule, or plant spore, of the very lowest order, which, multiplying its kind, gave birth to improved and enlarged offspring; and they, in their turn, grew, and multiplied, and differentiated into varieties; and so, in the course of endless ages, the poorer sorts perishing and the better sorts prospering, the world became filled with its existing populations, without any new creative acts of God, and without any particular providential care over the new species.
The particular process according to which this multiplication and improvement took place, Mr.Darwin calls Natural Selection.

Every creature tends to increase and multiply; and the very slowest breeders would soon fill the earth, were their multiplication not checked by hunger, by the attacks of enemies, and by the struggle for existence.
But all are not born alike strong, or swift, or of the same color; some of the same brood are better fitted to escape enemies, or to fight the battle of life, than others.

These will survive, while the weak ones perish.

This Mr.Wallace calls, the survival of the fittest.