Natural Selection

     When referring to evolution, it is a common misunderstanding that natural selection means "survival of the fittest". This saying alludes to the idea that only the strong members of a population will go on to survive and reproduce and that these organisms are some how better than those that did not pass on their genes. A better way to think of natural selection is in terms of fitness- both relative and absolute. Absolute fitness refers to the number of offspring an organism has over their entire life time and relative fitness refers to an organisms fitness in comparison to other members of the population. Essentially, fitness tells us how well an organism can both survive and reproduce. Because of this, it makes sense that natural selection simply refers to how well an organism can survive in order to produce offspring and contribute to the growth of the species. 

    If an organism is able to successfully reproduce, no matter how "strong" or "worthy" they are, they are "good enough". For example, considering two organisms- one of which is incredibly strong and well adapted to their environment and the other is seemingly less suited, you would assume due to the phrase "survival of the fittest" that the first organism would survive. However, the first organism dies before being able to reproduce and the second organism goes on to have ten offspring, the second organism is more "fit". The second organism is solely seen as more fit due to its ability to contribute to the population- this organism was able to pass on its genes to the next generation and subsequent generations. Due to this, it is hard to define natural selection as "survival of the fittest"; rather, it should be defined in terms of an organisms ability to successfully reproduce.