The person generally credited with originating the theory of evolution by natural selection is 1. A. B. C. D. E. Charles Barkley. Because elephants reproduce more slowly than mice, the mice have higher fitness. There is no fitness associated with a phenotype, only with the underlying genotype. An individual animal's fitness tends to increase as it gets older.
Fitness is calculated from both probability of survival and number of mates.
Natural selection 7. 11. frequently causes populations to go extinct. Fitness can be used to compare the adaptedness of different genotypes, but it is not an absolute measure of adaptedness. Adaptation is in part explained by organisms having internal drives to become more advanced and perfect. Traits shared among unrelated species living in the same habitat are likely to be adaptations.