Relative Fitness: Definition & Equation

Lesson Transcript
Instructor: Meredith Mikell

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.

The expression 'survival of the fittest' is less an issue of survival and more an issue of fitness. Relative fitness is a way of measuring the reproductive success of organisms within a population. Here we will explore the definition and equation that describe this concept.

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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