Natural selection

Definition

Natural selection is the process through which organisms that are better adapted to their environment tend to survive and reproduce more successfully than those that are less adapted. This concept is a key mechanism of evolution, explaining how species evolve over time based on the variations in traits that affect survival and reproduction. Natural selection operates on the genetic variation within populations, influencing the frequency of beneficial traits and shaping the diversity of life.

5 Must Know Facts For Your Next Test

1. Natural selection was first articulated by Charles Darwin in the 19th century and remains one of the cornerstones of evolutionary biology.
2. Natural selection acts on existing genetic variation within a population, favoring traits that enhance survival and reproductive success.
3. It is a gradual process that can lead to significant changes in populations over generations, contributing to the development of new species.
4. Natural selection can occur through various mechanisms, including stabilizing, directional, and disruptive selection, each affecting trait distributions in different ways.
5. Human activities, such as habitat destruction and pollution, can influence natural selection by altering environmental pressures and affecting which traits are advantageous.

Review Questions

• How does genetic variation contribute to the process of natural selection?
  • Genetic variation provides the raw material for natural selection by introducing differences among individuals in a population. When environmental pressures exist, such as changes in climate or availability of resources, certain traits may offer advantages for survival and reproduction. Those individuals with advantageous traits are more likely to survive and pass on their genes to the next generation, gradually leading to an increase in those beneficial traits within the population.
• Discuss the different mechanisms of natural selection and provide examples for each.
  • There are three main mechanisms of natural selection: stabilizing selection, directional selection, and disruptive selection. Stabilizing selection favors intermediate traits, reducing variation (e.g., human birth weights). Directional selection occurs when one extreme trait is favored over others (e.g., antibiotic resistance in bacteria). Disruptive selection favors both extremes over intermediate traits (e.g., beak sizes in finches on an island with two food sources). Each mechanism affects how populations evolve differently based on environmental pressures.
• Evaluate the impact of human-induced changes on natural selection and provide examples of how this influences evolution.
  • Human-induced changes have profound impacts on natural selection by altering habitats and introducing new selective pressures. For example, urbanization can lead to the emergence of city-adapted species, such as pigeons that thrive in urban environments. Additionally, pollution can create new challenges for organisms, such as fish that develop resistance to toxins. These alterations can accelerate evolutionary changes and lead to rapid adaptations in populations as they respond to changing conditions imposed by human activities.

Related terms

genetic variation: The diversity in gene frequencies among individuals within a population, which is essential for natural selection to occur.

adaptation: A trait that enhances an organism's ability to survive and reproduce in its environment, often resulting from the process of natural selection.

fitness: The relative ability of an organism to survive and reproduce in a given environment, often measured by the number of offspring produced.