<P> In the practice of mutual aid, which we can retrace to the earliest beginnings of evolution, we thus find the positive and undoubted origin of our ethical conceptions; and we can affirm that in the ethical progress of man, mutual support not mutual struggle--has had the leading part . In its wide extension, even at the present time, we also see the best guarantee of a still loftier evolution of our race . </P> <P> "Survival of the fittest" is sometimes claimed to be a tautology . The reasoning is that if one takes the term "fit" to mean "endowed with phenotypic characteristics which improve chances of survival and reproduction" (which is roughly how Spencer understood it), then "survival of the fittest" can simply be rewritten as "survival of those who are better equipped for surviving". Furthermore, the expression does become a tautology if one uses the most widely accepted definition of "fitness" in modern biology, namely reproductive success itself (rather than any set of characters conducive to this reproductive success). This reasoning is sometimes used to claim that Darwin's entire theory of evolution by natural selection is fundamentally tautological, and therefore devoid of any explanatory power . </P> <P> However, the expression "survival of the fittest" (taken on its own and out of context) gives a very incomplete account of the mechanism of natural selection . The reason is that it does not mention a key requirement for natural selection, namely the requirement of heritability . It is true that the phrase "survival of the fittest", in and by itself, is a tautology if fitness is defined by survival and reproduction . Natural selection is the portion of variation in reproductive success that is caused by heritable characters (see the article on natural selection). </P> <P> If certain heritable characters increase or decrease the chances of survival and reproduction of their bearers, then it follows mechanically (by definition of "heritable") that those characters that improve survival and reproduction will increase in frequency over generations . This is precisely what is called "evolution by natural selection ." On the other hand, if the characters which lead to differential reproductive success are not heritable, then no meaningful evolution will occur, "survival of the fittest" or not: if improvement in reproductive success is caused by traits that are not heritable, then there is no reason why these traits should increase in frequency over generations . In other words, natural selection does not simply state that "survivors survive" or "reproducers reproduce"; rather, it states that "survivors survive, reproduce and therefore propagate any heritable characters which have affected their survival and reproductive success". This statement is not tautological: it hinges on the testable hypothesis that such fitness - impacting heritable variations actually exist (a hypothesis that has been amply confirmed .) </P>

What is an example of survival of the fittest