Stabilizing selection

Definition

Stabilizing selection is a type of natural selection that favors intermediate variants of a trait, leading to a decrease in variation and maintaining the status quo in a population. This selection process tends to reduce the frequency of extreme phenotypes, promoting traits that provide a balance between fitness and stability within a specific environment. It plays a crucial role in the evolution of species by enhancing traits that contribute to survival and reproduction while minimizing the risks associated with extreme adaptations.

5 Must Know Facts For Your Next Test

1. Stabilizing selection is often observed in traits related to survival and reproduction, such as body size, where individuals with average sizes are more likely to thrive than those that are very large or very small.
2. This form of selection tends to maintain genetic diversity within a narrow range rather than eliminating it entirely, ensuring populations remain adaptable to environmental changes.
3. Examples of stabilizing selection can be seen in human birth weights, where infants with average weights have higher survival rates compared to those with very low or very high weights.
4. Stabilizing selection can lead to decreased variation over time, making populations more uniform in terms of certain traits, which may impact their adaptability to new challenges.
5. The concept of stabilizing selection highlights the importance of maintaining certain advantageous traits while balancing against extremes that could be detrimental to an organism's fitness.

Review Questions

• How does stabilizing selection influence the diversity of traits within a population over time?
  • Stabilizing selection reduces the frequency of extreme phenotypes while favoring intermediate variants, which leads to decreased genetic diversity over time. As this form of selection continuously promotes traits that are best suited for survival and reproduction in a given environment, it maintains a balance within the population. This ongoing process results in a more uniform trait distribution, making it less likely for extreme variations to persist within the gene pool.
• Discuss an example of stabilizing selection in human populations and its implications for health and fitness.
  • An example of stabilizing selection in human populations is seen in birth weights. Infants with average birth weights tend to have higher survival rates compared to those who are either underweight or overweight at birth. This has implications for health as it suggests that there is an optimal range for birth weight, reflecting how stabilizing selection works to promote traits that enhance fitness and survival in humans. Over generations, this selective pressure has likely contributed to the prevalence of average birth weights within human populations.
• Evaluate the potential long-term consequences of stabilizing selection on a population's ability to adapt to environmental changes.
  • While stabilizing selection helps maintain advantageous traits by reducing variability, it can also lead to decreased adaptability in the long term. If environmental conditions shift significantly, populations that have become uniform may struggle to cope with new challenges since they lack the genetic diversity necessary for rapid adaptation. This situation could render them vulnerable to changes such as climate shifts or new diseases, highlighting the need for genetic variation as a buffer against evolving threats.

Related terms

Directional selection: A type of natural selection that favors one extreme phenotype over others, causing a shift in allele frequencies in a particular direction.

Disruptive selection: A form of natural selection that favors extreme phenotypes at both ends of the spectrum, potentially leading to speciation as intermediate phenotypes are selected against.

Genetic variation: The diversity of alleles and genotypes within a population, which is essential for natural selection and evolutionary processes.