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05 Evolution

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Topic 5: Evolution and biodiversity

This is an introduction to the evolution and biodiversity topic. It lists understandings and skills expected for Topic 5 including the evidence for evolution, natural selection, classification and cladistics. Helpful for revision.
Detailed revision notes, activities and questions can be found for each of the sub-topic pages:

  • 5.1 Evidence for evolution
  • 5.2 Natural selection
  • 5.3 Classification of biodiversity
  • 5.4 Cladistics

5.1 Evidence for evolution

  • A change in the heritable characteristics of a species is evolution.
  • Evidence for evolution comes from
    • the fossil record.
    • Selective breeding of domesticated animals
    • "Adaptive radiation" can explain similar structures with different functions.
    • Isolated populations can produce separate species by divergent evolution.
    • Continuous variation across the geographical range of related populations matches the concept of gradual divergence.

Skills (can you ....)

  • Describe how the dark bark leads to the development of melanistic insects in polluted areas.
  • Compare and contrast the pentadactyl limb of mammals, birds, amphibians and reptiles.
  • Describe how each limb structure is adapted to each different method of locomotion.

5.2 Natural selection

  • Natural selection requires;
    • variation in adaptations within a species.
    • overproduction of offspring
    • best adapted individuals have better survival rates
    • so they reproduce more and pass on successful adaptations to offspring.
  • Variation within a species can be caused by Mutation, meiosis and sexual reproduction.
  • Adaptations are advantageous characteristics of an individual for it's way of life.
  • More offspring are produced by the best adapted individuals while less well adapted individuals die or produce fewer offspring.
  • Adaptations / characteristics are passed on to offspring (inheritance).
  • Natural selection increases the frequency of the better adaptations and decreases the frequency of other characteristics. This leads to changes in characteristics within the species

Skills (can you ....)

  • Analyse data about the changes in beak lengths of finches on Daphne Major.
  • Understood how the evolution of antibiotic resistance in bacteria occurs by natural selection.

5.3 Classification of biodiversity

  • The binomial system of scientific names is used across the world. It was agreed by biologists at a series of congresses,
  • When a species is discovered it is given a scientific (binomial) name.
  • Taxonomists classify species using a hierarchy of taxa.
  • All organisms are classified into three domains; Archaea (called archaeans), eubacteria (bacteria) and eukaryote (eukayotes). (Viruses are not classified as living)
  • Eukaryotes are classified into the main taxa: kingdom, phylum, class, order, family, genus and species.
  • In a natural classification, the genus and accompanying higher taxa consist of all the species that have evolved from one common ancestral species.
  • This natural classification helps identification of species and the prediction of shared characteristics by related species.
  • Taxonomists sometimes reclassify groups of species when new evidence about evolution appears.

Skills (can you ....)

  • Classify one plant and one animal species from domain to species level.

  • Remember and recognise the main features of:

    • bryophyta, filicinophyta, coniferophyta and angiospermophyta.(including vascular tissue

    • porifera, cnidaria, platylhelmintha, annelida, mollusca, arthropoda and chordata.

      • birds, mammals, amphibians, reptiles and fish.

  • Construct a dichotomous key for use in identifying specimens.

5.4 Cladistics

  • A clade is a group of organisms that have evolved from a common ancestor.
  • Evidence for species of a clade can be
    • the base sequences of a gene or
    • the amino acid sequence of a protein.
  • There is a gradual accumulation of differences and a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor.
  • Cladograms are tree diagrams that show the most probable sequence of divergence in clades.
  • Evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group or species.
  • Traits can be analogous (due to convergent evolution) or homologous (inherited from a common ancestor).

Skills (can you ....)

  • Interpret and deduce relationships from cladograms including humans and other primates.

  • Appreciate that in the light of new evidence some cladograms are changed.

  • For example the reclassification of the figwort family using evidence from cladistics.


  • Cladistics 5.4

    Cladistics is the study of the family relationships between different classification groups. A clade is a group containing all the descendants of an ancestor species. Understanding the evidence used to build cladograms is also required.

  • Classification of biodiversity 5.3

    Classification helps biologists wherever they are to group organisms into species sharing similar characteristics and share their ideas with others. A basic understanding of the main grouping and their basic features is covered in this topic.

  • Evidence for evolution 5.1

    There are different types of evidence which support the theory of evolution, from fossils to selective breeding. This topic covers a range of evidence and some of the concepts related to inheritance, natural selection and evolution.

  • Natural selection 5.2

    Natural selection increases the frequency of successful adaptations in a species and it relies on variation in the features as well as overproduction of offspring, a struggle for survival and survival of the fittest.