3.2 Origins of biodiversity

Significant ideas:

  • Evolution is a gradual change in the genetic character of populations over many generations, achieved largely through the mechanism of natural selection.
  • Environmental change gives new challenges to species, which drives the evolution of diversity.
  • There have been major mass extinction events in the geological past.

Knowledge and understanding:

  1. Biodiversity arises from evolutionary processes.
  2. Biological variation arises randomly and can either be beneficial to, damaging to, or have no impact on, the survival of the individual.
  3. Natural selection occurs through the following mechanism:
    • a. Within a population of one species, there is genetic diversity, which is called variation.
    • b. Due to natural variation, some individuals will be fitter than others.
    • c. Fitter individuals have an advantage and will reproduce more successfully than individuals who are less fit.
    • d. The offspring of fitter individuals may inherit the genes that give that advantage.
  4. This natural selection will contribute to the evolution of biodiversity over time.
  5. Environmental change gives new challenges to species: those that are suited will survive, and those that are not suited will not survive.
  6. Speciation is the formation of new species when populations of a species become isolated and evolve differently from other populations.
  7. Isolation of populations can be caused by environmental changes forming barriers such as mountain formation, changes in rivers, sea level change, climatic change or plate movements. The surface of the Earth is divided into crustal, tectonic plates that have moved throughout geological time. This has led to the creation of both land bridges and physical barriers with evolutionary consequences.
  8. The distribution of continents has also caused climatic variations and variation in food supply, both contributing to evolution.
  9. Mass extinctions of the past have been caused by various factors, such as tectonic plate movements, super-volcanic eruption, climatic changes (including drought and ice ages), and meteorite impact—all of which resulted in new directions in evolution and therefore increased biodiversity.

Applications and skills:

  • Explain how plate activity has influenced evolution and biodiversity.
  • Discuss the causes of mass extinctions.


  • Within the human population, distinct characteristics have evolved within different populations through natural selection and exposure to the environmental conditions that were unique to the regions of those populations. How has globalization altered some of the environmental factors that were formerly unique to different human populations?
  • Human impact has increased the rate at which some mass extinctions have occurred on a global scale.

Theory of knowledge:

  • The theory of evolution by natural selection tells us that change in populations is achieved through the process of natural selection—is there a difference between a convincing theory and a correct one?


  • Biomes, zonation and succession (2.4)
  • Climate change—causes and impacts (7.2)