Darwin’s great contribution was a theory to account for the great diversity of species that are observed on this earth. His prime contribution is NOT an evolutionary theory of the “origin” of species. It is a theory that accounts for the variability of observed species in our day and age, and it tries to account for why some species die off (become extinct) and other species do not. He called it a theory of natural selection or survival of the fittest. It's a theory of speciation, not a theory of the evolutionary origin of species. In modern terms I prefer to state Darwin’s Laws as follows:
I. Every living organism, representing a member of any given specie, has been genetically designed with organic adaptations that are conducive (statistically) to its survival in its environmental niche. (By Darwin’s definition the survival of the fittest (in an environmental niche) refers to reproductive success in perpetuating the specie)
II. Every living organism, representing or member of any given specie, has been genetically designed with behavioral drives that are conducive (statistically) to its survival in its environmental niche. (By Darwin’s definition the survival of the fittest (in an environmental niche) refers to behavior patterns that lead to reproductive success in perpetuating the specie).