Is Natural Selection Random?

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Natural selection, the process by which species adapts to their environment through changes in genetics, is not random. Through years of evolution, natural selection boosts the biological traits that help animals and plants survive in their particular environment, and weeds out the traits that make survival more difficult.

However, the genetic changes (or mutations) that are filtered by natural selection do come about randomly. In this sense, natural selection contains both random and non-random components.

Key Takeaways

  • Introduced by Charles Darwin, natural selection is the idea that a species adapts to its environment through changes in its genetics.
  • Natural selection is not random, though the genetic changes (or mutations) that are filtered by natural selection do come about randomly.
  • Some case studies–for example, peppered moths–have directly shown the impacts or processes of natural selection.

How Natural Selection Works

Natural selection is the mechanism by which species evolve. In natural selection, a species acquires genetic adaptations that will help them survive in their environment, and pass those favorable adaptations to their offspring. Eventually, only individuals with those favorable adaptations will survive.

One notable, recent example of natural selection is elephants in areas where the animals are being poached for ivory. These animals are giving birth to fewer children with tusks, which may give them a better chance of survival.

Charles Darwin, the father of evolution, figured out natural selection by witnessing several key observations:

  • There are many traits–which are qualities or properties that characterize an organism. These traits, furthermore, can vary in the same species. For example, in one area you may find some butterflies that are yellow and others that are red.
  • Many of these traits are heritable and can be passed from parents to offspring.
  • Not all organisms survive since an environment has limited resources. For example, the red butterflies from above tend to be eaten by birds, causing there to be more yellow butterflies. These yellow butterflies reproduce more and they become more common in the next generations.
  • Over time, the population has adapted to its environment–later on, the yellow butterflies will be the only type around.

A Caveat of Natural Selection

Natural selection is not perfect. The process does not necessarily select for the absolute best adaptation there could be for a given environment, but does yield traits that work for a given environment. For example, birds have more effective lungs than humans, which allow birds to take in more fresh air and are overall more efficient in terms of air flow.

Furthermore, a genetic trait that was once considered more favorable may be lost if it is no longer useful. For example, many primates cannot produce vitamin C because the gene corresponding to that trait was inactivated through mutation. In this case, the primates typically live in environments where vitamin C is easily accessible.

Genetic Mutations are Random

Mutations–which are defined as changes in a genetic sequence–occur randomly. They can help out, harm, or not affect an organism at all, and will occur no matter how detrimental or beneficial it may be for a certain organism.

The rate of mutations can change depending on the environment. For example, exposure to a harmful chemical may increase an animal’s rate of mutation.

Natural Selection in Action

Though natural selection is responsible for many of the traits we see and encounter, some case studies have directly shown the impacts or processes of natural selection.

Galapagos Finches

During Darwin’s travels in the Galapagos Islands, he saw several variations of a type of bird called a finch. Though he saw that the finches were very similar to one another (and to another type of finch he had seen in South America), Darwin noted that the finches’ beaks helped the birds eat specific types of food. For instance, finches that ate insects had sharper beaks to help catch bugs, while finches that ate seeds had stronger and thicker beaks.

Peppered Moths

An example can be found with the peppered moth, which can only be either white or black, and whose survival depends on their ability to blend in with their surroundings. During the Industrial Revolution–when factories were contaminating the air with soot and other forms of pollution–people noted that white moths dwindled in number whereas black moths became much more common.

A British scientist then performed a series of experiments showing that black moths were growing in number because their color allowed them to blend in better with the soot-covered areas, protecting them from being eaten by birds. To support this explanation, another (initially doubtful) scientist then showed that white moths were eaten less in an unpolluted area, while black moths were eaten more.


  • Ainsworth, Claire, and Michael Le Page. “Evolution’s Greatest Mistakes.” New Scientist, New, 8 Aug. 2007,
  • Feeney, William. “Natural Selection in Black and White: How Industrial Pollution Changed Moths.” The Conversation, The Conversation US, 15 July 2015,
  • Le Page, Michael. “Evolution Myths: Evolution Produces Perfectly Adapted Creatures.” New Scientist, New Scientist Ltd., 10 Apr. 2008,
  • Le Page, Michael. “Evolution Myths: Evolution Is Random.” New Scientist, New Scientist Ltd., 16 Apr. 2008,
  • Maron, Dina Fine. “Under Poaching Pressure, Elephants Are Evolving to Lose Their Tusks.”, National Geographic, 9 Nov. 2018,
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Lim, Alane. "Is Natural Selection Random?" ThoughtCo, Sep. 2, 2021, Lim, Alane. (2021, September 2). Is Natural Selection Random? Retrieved from Lim, Alane. "Is Natural Selection Random?" ThoughtCo. (accessed June 9, 2023).