Variation and Evolution

Variation and Evolution


  • Variation is the existence of differences between individuals within a species. It can either be genetic or environmental.
  • Genetic variation is caused by differences in genes or chromosomes, dictating the organisms’ phenotype such as skin, eyes and hair colour.
  • Environmental variation is caused by factors that impact an organism’s development. It includes nutrition, temperature, light levels or lifestyle factors.
  • Continuous variation show a complete range of measurements from one extreme to another within a population such as human height.
  • Discontinuous variation have distinct classes or categories, such as blood type or sex.

Causes of Genetic Variation

  • Mutation involves changes in the structure or amount of an organism’s DNA, often resulting in new genetic variability.
  • Meiosis is a type of cell division that produces four daughter cells. This process introduces genetic variation via independent assortment and crossing over.
  • Fertilisation also leads to variation because it combines the genetic material of two organisms yielding diverse offspring.


  • Understanding evolution means acknowledging how species originate, evolve over time, and become extinct.
  • Natural selection, sometimes referred to as survival of the fittest, describes how better adapted individuals within a population have a higher chance of survival and, consequently, passing on their advantageous traits to their offspring.
  • Evolutionary adaptation is the process via which a species adapts to its environment over time, driven by natural selection.
  • Speciation happens when populations evolve to become distinct species. This could occur due to geographic isolation, reproductive isolation or through genetic divergence.

Understanding Evolutionary Trees

  • Evolutionary trees, or phylogenetic trees, illustrate the relationships between different species, demonstrating how each species has evolved from a common ancestor.
  • Each branching point, dubbed a node, on the tree represents a common ancestor from which the species diverged.
  • Species that share a recent common ancestor and closely related are known as sister groups.
  • The length of the branches often represents the amount of genetic change, so longer branches show more change.

Examining Evolutionary Evidence

  • Paleontology involves studying fossils to understand how species have evolved over time.
  • Comparative anatomy focuses on comparing the structures of different species to examine their evolutionary relationships, for instance looking at homologous and analogous structures.
  • Embryological evidence looks at the development of organisms before birth or hatching to find common ancestry.
  • Molecular biology gives us the ability to compare DNA and protein sequences between species, which is currently the most accurate source of evidence for relationships between species.