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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.

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.

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• 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

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.

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).