Natural Selection

Understanding Natural Selection

  • Natural selection is a key mechanism of evolution, the process that leads to changes in species over generations.
  • Proposed by Charles Darwin, natural selection explains how species evolve and adapt to their environment.
  • It operates on the principle of survival of the fittest. The term “fittest” refers to those individuals who are best adapted to their environment.

How Natural Selection Works

  • Variation exists within all populations of organisms due to genetic differences.
  • Throughout their lifetimes, organisms have to struggle for key resources such as food, mates, and habitat.
  • Only the individuals with the most beneficial traits for a particular environment are likely to survive and reproduce.
  • The beneficial traits from these survivors are then passed on to their offspring.
  • Over numerous generations, these advantageous traits become more common in the population, leading to an evolutionary adaptation.

Types of Natural Selection

  • In Directional selection, individuals at one extreme of the characteristic range have a survival advantage. This shifts population characteristics in that direction.
  • Stabilising selection favours individuals with an average value of a characteristic. Survivors are those that are most typical with fewer extremes in the population.
  • Disruptive selection favours individuals at either extreme of the population distribution, resulting in two peaks in the population for that trait.

Evidence of Natural Selection

  • Fossil records can show changes in species over time, indicating evolution through natural selection.
  • Comparative anatomy, such as homologous structures (similar structures in different species hinting common ancestry) and vestigial structures (structures with no/limited function in a species, hinting evolutionary change) provide evidence.
  • The study of DNA and protein structures can show relationships between species, indicating common ancestry and divergence through natural selection.

Impact of Natural Selection

  • Natural selection can lead to speciation, the formation of a new species.
  • It contributes to biodiversity, the variety of life forms on Earth.
  • It can also affect population dynamics, the way populations of species fluctuate in size and composition over time.