4 Necessary Factors of Natural Selection

Most people in the general population can at least explain that Natural Selection is something that is also called "Survival of the Fittest". However, sometimes, that is the extent of their knowledge on the subject. Others may be able to describe how individuals that are better suited to survive in the environment they live in will live longer than those who aren't. While this is a good start to understanding the full extent of Natural Selection, it is not the entire story.

Before jumping into what all Natural Selection is (and isn't, for that matter), it is important to know what factors must be present in order for Natural Selection to work in the first place. There are four main factors that must be present in order for Natural Selection to happen in any given environment.

01
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Overproduction of Offspring

Reproducing like bunnies
Getty/John Turner

The first of these factors that must be present in order for Natural Selection to occur is the ability of a population to overproduce offspring. You may have heard of the phrase "reproduce like rabbits" which means to have a lot of offspring quickly, much like it seems rabbits do when they mate. 

The idea of overproduction was first incorporated into the idea of Natural Selection when Charles Darwin read Thomas Malthus's essay on human population and the food supply. The food supply increases linearly while the human population increases exponentially. There would come a time when the population would pass up the amount of available food. At that point, some humans would have to die out. Darwin incorporated this idea into his ​Theory of Evolution through Natural Selection.

Overpopulation doesn't necessarily have to occur in order for Natural Selection to happen within a population, but it must be a possibility in order for the environment to put selective pressure on the population and some adaptations to become desirable over others.

Which leads to the next necessary factor...

02
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Variation

Domestic Dogs
Getty/Mark Burnside

Those adaptations that are occurring in individuals due on a small scale to mutations and being expressed due to the environment contribute variation of alleles and traits to the overall population of the species. If all individuals in a population were clones, then there would be no variation and therefore no Natural Selection at work in that population.

Increased variation of traits in a population actually increases the likelihood of survival of a species as a whole. Even if part of a population is wiped out due to various environmental factors (disease, natural disaster, climate change, etc.), it is more likely that some individuals would possess traits that would help them survive and repopulate the species after the dangerous situation has passed.

Once enough variation has been established, then the next factor comes into play...

03
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Selection

Bottlenose dolphin (Tursiops truncatus).
Martin Ruegner / Getty Images

It is now time for the environment to "choose" which of the variations is the one that is advantageous. If all variations were created equal, then Natural Selection again would not be able to happen. There must be a clear advantage to having a certain trait over others within that population or there is no "survival of the fittest" and everyone would survive.

This is one of the factors that can actually change during the lifespan of an individual in a species. Sudden changes in the environment may happen and therefore which adaptation is actually the best one would also change. Individuals that were once thriving and considered the "fittest" may now be in trouble if they are no longer suited as well to the environment after it changes.

Once it has been established which is the favorable trait, then...

04
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Reproduction of Adaptations

A peacock showing his eyespots
Getty/Rick Takagi Photography

Individuals that possess those favorable traits will live long enough to reproduce and pass down those traits to their offspring. On the other side of the coin, those individuals that lack the advantageous adaptations will not live to see their reproductive periods of their lives and their less desirable characteristics will not be passed down.

This changes the allele frequency in the population's gene pool. There will eventually be less of the undesirable traits seen as those poorly suited individuals do not reproduce. The "fittest" of the population will pass down those traits during reproduction to their offspring and the species as a whole will become "stronger" and more likely to survive in their environments.

This is the aim of Natural Selection. The mechanism for evolution and creation of new species is dependent upon these factors to make it happen.

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Scoville, Heather. "4 Necessary Factors of Natural Selection." ThoughtCo, Apr. 13, 2017, thoughtco.com/necessary-factors-of-natural-selection-1224587. Scoville, Heather. (2017, April 13). 4 Necessary Factors of Natural Selection. Retrieved from https://www.thoughtco.com/necessary-factors-of-natural-selection-1224587 Scoville, Heather. "4 Necessary Factors of Natural Selection." ThoughtCo. https://www.thoughtco.com/necessary-factors-of-natural-selection-1224587 (accessed January 22, 2018).