Fitness and Selection

     An organisms fitness is an extremely important aspect to their survival and can impact the success of the overall species. Absolute fitness refers to the number of offspring an organism has over their entire lifetime. When comparing the absolute fitness of a species, individuals that produce more viable offspring are more fit than those that produce fewer or even no offspring. This comparison of absolute fitness is an organisms relative fitness. Relative fitness is the fitness in comparison to other members of the population- this fitness is the survival of the good enough. While these two types of fitness can be related, they can also be extremely different. One organism that produces 10 viable offspring may have a better absolute fitness when compared to another member of the same species if they only produce 3 offspring; however, the organism that produces 10 viable offspring may have a lower relative fitness when compared to other members of the population that produce 20 viable offspring. 

    In the case of these cats, cat 1 has greater absolute fitness than cat 2 but does not have the highest relative fitness- cat 3 has the highest relative fitness. 

    Once an organism produces viable offspring, its heritable traits will be passed onto that offspring. If these traits that are passed onto the offspring are beneficial, the spread of these beneficial alleles is known as positive selection. When an organisms beneficial traits are passed on, they can be changed throughout time due to mutations during replication. These mutations can happen any time during replication and can alter the organisms traits and overall ability to reproduce. Such traits may now be changed to be even more beneficial or detrimental to the organism and its ability to produce offspring. 

    Due to a mutation, the offspring of the cat has a blue tail tip, rather than a pink tail tip. The blue tail tip may or may not be more beneficial to the cat species and this can potentially impact the cats absolute and relative fitness. If the trait is less beneficial, that offspring may not reproduce which will allow more pink-tailed cats to survive and reproduce. This passing-on of pink tails is positive selection. This does not mean that pink-tailed cats will always have higher fitness, a random mutation could come along and produce yellow-tailed cats that reproduce significantly more than pink-tailed cats. All of these mutations and changes happen over variable amounts of time and it is unknown which potential tail color produces the most "fit" cats.