Variation and Natural Selection

Variation and Natural Selection

Section 1: Principles of Variation

  • Variation refers to the differences that can be observed within a species.
  • Variation can be genetic or environmental, or a result of both.
  • Genetic variations are caused by differences in an organism’s genes or mutations.
  • Environmental variations (also known as acquired characteristics) are features or traits determined by an individual’s environment or experiences.
  • Inherited characteristics are passed from parent to offspring through genes.

Section 2: Genetic Variation and Mutation

  • Genetic variation is important for evolution to occur.
  • Mutations are accidental changes to genes and chromosomes, and they provide a source of new genetic variation.
  • Some mutations may be beneficial and increase an organism’s chance of survival.
  • There are two broad types of genetic variation: discontinuous and continuous. Discontinuous variation shows distinct categories and is controlled by a single gene. Continuous variation shows a range of characteristics and is usually controlled by several genes.

Section 3: Natural Selection and Survival of the Fittest

  • Natural selection, also known as survival of the fittest, is a key mechanism of evolution.
  • It describes the process where organisms best suited to their environment are more likely to survive and reproduce, passing on their beneficial traits to their offspring.
  • This selective pressure encourages the spread of beneficial traits in successive generations, leading to evolution.
  • Traits which decrease an organism’s chance of survival will tend to become less common over time due to natural selection.
  • Both selective breeding (artificial selection) and natural selection can cause changes in a species over time.

Section 4: Evolution as a Result of Natural Selection

  • Evolution is a process that leads to changes in the inherited characteristics of a species over many generations.
  • Evolution doesn’t occur in individuals but across populations.
  • It results from natural selection acting upon genetic variation within a population.
  • Evidence supporting the theory of evolution includes: the fossil record, DNA sequencing, and observation of change in species over time due to selective pressures.

Section 5: Adaptation and Speciation

  • Adaptation refers to the process by which a species becomes better suited to its environment, often over many generations.
  • The process of natural selection encourages adaptations that increase an organism’s chance of survival and reproduction.
  • Speciation is the formation of a new species. It often occurs when a part of a population becomes separated, making interbreeding impossible.
  • Over time, genetic variants accumulate in the separated population, leading to new adaptations and, eventually, a new species.