Survival Of The Fitness: Natural Selection Explained

Explaining Darwin's theory in today's terminology.

Natural selection does not mean “survival of the fittest”

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There is a common misconception that natural selection means the stronger or bigger something is, the more likely it is to survive than something else. This is not true.

Natural selection isn’t not about an individual being the fastest, strongest or biggest

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It's about things that allow an individual to reproduce and pass on their traits to their offspring. This is what biologists mean by fitness. In many cases, fitness is measured by the number of offspring that an individual produces. Animals that are smaller require less food, so in cases that there is a lack of resources, those who require less will survive. When the mass extinction that included dinosaurs occurred, the mammals that were smaller thrived in the scarcity of resources.

Natural selection doesn’t “choose” traits

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A common misconception about natural selection is that it “chooses” the strongest traits that make the individual the most fit for its environment, but natural selection is not a conscious process. The features that it selects for are usually beneficial in the environment, but they are not necessarily the “best” traits.

Natural selection doesn’t create the perfect specimen

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Even if a trait is beneficial, that doesn’t mean that there are not trade offs due to this trait. A trade off would be exchanging a helpful trait for a physical consequence. For example, cheetahs can run quickly, but not for long distances. If a cheetah were to increase speed, it would need longer legs. This makes the bone more likely to break. So even though the cheetah is now “faster”, its fitness may not also increase.

Another example of a trade off is sickle cell disease, which is common in areas that are high in malaria. The sickle cell mutation, now referred to as an allele, can cause people to have more resistance to malaria, but only if they have one copy of it. (People have two copies of alleles) People with two copies of the sickle cell allele and people with no sickle cell disease no copies are more susceptible to malaria than people with only one copy of it.

Natural selection selects for a fit enough trait in the environment not the “fittest” trait

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Environments are a huge contributing factor to what traits natural selection will select for. Traits can be fit for one environment, but not fit for another. An example of this is the pocket mouse coat color selection. Mice with dark coat color found on dark lava could hide more easily from predators than mice with lighter coats. Because of this, more of the dark mice survived to reproduce and pass on the darker coat color. Over time, the average mice coat color changed as darker coat color proved to be more fit. On the light rock, however, the light mice are more fit than the dark mice because the light mice are better able to hide on the light rocks. The ability to hide from predators on the light rocks lets the light mice reproduce more than the dark mice, causing them to have a higher fitness in that environment.

SO...

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Natural selection isn’t survival of the fittest. It is the selection of traits based on fitness. Fitness is the ability of an organism to reproduce. This allows traits to be passed on to the next generation. The fitness of these traits may be based on how they allow individuals to survive in an environment. These traits are not the ideal. They are not perfection. Natural selection isn’t survival of the fittest. It is survival of the fit enough.

And that's how natural selection works

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