If we wish to know how a fish can become a man, it is not instructive to be told that the organisms that leave the most offspring are the ones that leave the most offspring. Some statements on behalf of evolution and the process of natural selection reduce to something essentially equivalent. The following deductive argument is found in the British Natural History Museum's handbook on evolution, by Colin Patterson. All organisms must reproduce to survive. All organisms exhibit hereditary variations.
Hereditary variables differ in their effect on reproduction.
Therefore, variations with favorable effects on reproduction will succeed and those with unfavorable effects will fail and the organism will change. Without this addition there is nothing here to support evolution. However, the assertion is added without support. Actually natural selection may be more responsible for stability than for change. That the effect of natural selection may be to keep a species from changing is not merely a theoretical possibility.