Examples of Stabilizing Selection in Evolution

Evolution is a process that drives changes in populations over time. One mechanism of evolution is natural selection, which acts on the variation within a population. Stabilizing selection is a type of natural selection that favors the average phenotype and reduces the extremes. In this article, we will explore examples of stabilizing selection in various organisms and highlight how it contributes to the maintenance of well-adapted populations.

Human Birth Weight

One classic example of stabilizing selection is human birth weight. Babies born with very low birth weight or very high birth weight often face increased health risks. Stabilizing selection acts to favor babies with an average birth weight, as they tend to have the highest chances of survival and overall health. This is because extremely low birth weight babies may struggle with underdeveloped organs and increased vulnerability to infections, while extremely high birth weight babies may face complications during birth.

Beak Size in Birds

Birds with beaks that are too small may struggle to efficiently gather food, while birds with beaks that are too large may have difficulty manipulating and consuming their food. Stabilizing selection acts to favor birds with an average beak size that is well-suited to their specific feeding habits and available food sources. For example, in a population of finches, those with beaks of intermediate size may have the highest fitness, as they can effectively utilize a wider range of food resources.

Butterfly Wing Coloration

Butterflies often exhibit a wide range of wing coloration patterns. In some cases, stabilizing selection acts to favor individuals with intermediate coloration, as they may have a better chance of blending in with their environment and avoiding predation. Butterflies with extremely bright or extremely dull wing coloration may be more easily spotted by predators or may struggle to attract mates, respectively.

Plant Leaf Size

In plant populations, stabilizing selection can be observed in traits such as leaf size. Plants with leaves that are too small may have limited surface area for photosynthesis, while plants with leaves that are too large may experience excessive water loss or be more susceptible to damage from wind or herbivores. Stabilizing selection favors plants with an average leaf size that balances the need for efficient photosynthesis and protection against environmental stressors.


Stabilizing selection is an important mechanism in evolution that acts to maintain the average phenotype within a population. Examples such as human birth weight, bird beak size, butterfly wing coloration, and plant leaf size demonstrate how stabilizing selection contributes to the overall fitness and adaptation of organisms. By favoring individuals with intermediate traits, stabilizing selection helps to ensure that populations are well-suited to their specific environments and can thrive in the face of selective pressures.

FAQs about Selection in Evolution

What is selection in evolution?

Selection in evolution refers to the process by which certain traits or characteristics become more or less common in a population over time. It is one of the key mechanisms driving the process of natural selection, which is the central concept in evolutionary biology. Selection occurs when certain traits confer a reproductive advantage, increasing an organism’s chances of survival and successful reproduction.

What are the different types of selection?

There are several types of selection that can influence the evolution of a population:

  • 1. Natural Selection: Natural selection occurs when certain heritable traits increase an organism’s chances of survival and reproduction in a particular environment. Individuals with advantageous traits are more likely to survive and pass on their genes to the next generation, leading to an increase in the frequency of those traits over time.
  • 2. Artificial Selection: Artificial selection, also known as selective breeding, is the process in which humans intentionally select and breed individuals with desirable traits to produce offspring with those traits. This practice has been used for centuries in agriculture and animal breeding to enhance specific characteristics in domesticated plants and animals.
  • 3. Sexual Selection: Sexual selection occurs when certain traits increase an organism’s chances of mating and reproductive success. It can involve competition between individuals of the same sex (intrasexual selection) or the preference of one sex for certain traits in the opposite sex (intersexual selection). Sexual selection often leads to the evolution of elaborate ornaments, behaviors, or secondary sexual characteristics.
  • 4. Stabilizing Selection: Stabilizing selection occurs when individuals with intermediate phenotypes have a higher fitness compared to those with extreme phenotypes. This type of selection reduces genetic variation in a population and maintains a stable average phenotype.
  • 5. Directional Selection: Directional selection occurs when individuals with extreme phenotypes have a higher fitness compared to those with intermediate phenotypes. This type of selection can lead to a shift in the average phenotype of a population over time.
  • 6. Disruptive Selection: Disruptive selection occurs when individuals with extreme phenotypes have a higher fitness compared to those with intermediate phenotypes. This type of selection can lead to the splitting of a population into two or more distinct phenotypic groups.

How does selection influence evolution?

Selection plays a crucial role in shaping the genetic makeup of populations over time. When certain traits provide a selective advantage, individuals with those traits are more likely to survive, reproduce, and pass on their genes to the next generation. As a result, the frequency of advantageous traits increases in the population, while the frequency of disadvantageous traits decreases. This process leads to the gradual evolution of populations, as the genetic composition changes in response to selective pressures.

Selection can drive the adaptation of organisms to their environments, allowing them to better survive and reproduce in specific conditions. It can lead to the development of complex adaptations, such as camouflage, enhanced foraging abilities, or resistance to diseases. Selection can also result in the divergence of species, as populations adapt to different ecological niches or undergo reproductive isolation.

Can selection lead to the extinction of traits or species?

Yes, selection can lead to the extinction of traits or even entire species. If certain traits become disadvantageous due to changes in the environment or other factors, individuals with those traits may have reduced fitness and reproductive success. Over time, the frequency of those traits in the population decreases, and they may eventually disappear altogether.

Similarly, if a species fails to adapt to changing conditions or faces intense selective pressures, it may become extinct. Extinction can occur when a species is unable to compete with other species, is unable to find suitable mates, or experiences significant changes in its habitat or ecosystem.

It is important to note that extinction is a natural part of the evolutionary process, and new traits and species can emerge through the ongoing process of selection and adaptation.

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