Meredith holds a B.S. in marine science with a minor in philosophy, as well as a master's of aeronautical science with a space science emphasis. She has taught subjects including marine science, biology, astronomy, math, and reading to students from kindergarten through high school.
Background on Evolutionary Fitness
The concept of 'itness in biology is a bit different than the common use of the word. We aren't talking about muscle tone or cardiovascular ability. Fitness refers to how well an organism passes on its genes to the next generation. Basically, it's number of offspring, assuming they survive long enough to then have offspring of their own. This number is described as the absolute fitness of the organism. But this raw number doesn't mean much unless we know how many offspring other members of the population typically have. If dolphins typically have three babies in their lifetime, and a particular dolphin has four babies, she has a higher relative fitness. Relative fitness refers to the absolute fitness of the organism divided by the average number of offspring in a given population.
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Some Information on Genotypes
This concept is often also applied to a particular genotype, a genetic variant within a population. In our dolphin example, a genotype might cause a phenotype, or the characteristics that we all can see on the surface, be a certain color, speckles, or body shape that has a more or less dominant presence in the population relative to other genotypes. This can depend on whether or not that genotype is beneficial to the survival and reproduction of the organisms who have it. Perhaps a darker dolphin is less visible to predators, or a more narrow torso allows for more streamlined swimming and catching fish. Whether or not the genotype is passed along to offspring depends on the genotype of both parents and the dominance of their particular genes.
Equation of Relative Fitness
Relative fitness is shown below as the absolute fitness divided by the average fitness and is usually expressed as a ratio.
We've used the dolphin example before, and it shows that the absolute fitness of the population, 4, divided by the average fitness of the population, 3, gives us a relative fitness of 1.33.
Relative fitness describes the total number of offspring an organism has compared to the average number of offspring for the population. In equation form, it's:
Relative fitness = (absolute fitness) / (average fitness)
The absolute fitness describes the total number of offspring of two given organisms. It is useful in understanding just how successful that organism is at passing on its genes. 'Survival of the fittest' should really be called 'reproduction of the fittest!' They not only pass on their genotypes, which are genetic variants within a population, but also the phenotypes, which are the characteristics that we all can see on the surface.
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Relative Fitness: Definition & Equation
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