SL Content Statements

• A4.1.1

  Evolution as change in the heritable characteristics of a population

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  This definition helps to distinguish Darwinian evolution from Lamarckism. Acquired changes that are not genetic in origin are not regarded as evolution.
  NOS: The theory of evolution by natural selection predicts and explains a broad range of observations and is unlikely ever to be falsified. However, the nature of science makes it impossible to formally prove that it is true by correspondence. It is a pragmatic truth and is therefore referred to as a theory, despite all the supporting evidence.
  

• A4.1.2

  Evidence for evolution from base sequences in DNA or RNA and amino acid sequences in proteins

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  Sequence data gives powerful evidence of common ancestry.
  

• A4.1.3

  Evidence for evolution from selective breeding of domesticated animals and crop plants

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  Variation between different domesticated animal breeds and varieties of crop plant, and between them and the original wild species, shows how rapidly evolutionary changes can occur.

• A4.1.4

  Evidence for evolution from homologous structures

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  Include the example of pentadactyl limbs.

• A4.1.5

  Convergent evolution as the origin of analogous structures

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  Students should understand that analogous structures have the same function but different evolutionary origins. Students should know at least one example of analogous features.
  

• A4.1.6

  Speciation by splitting of pre-existing species
  

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  Students should appreciate that this is the only way in which new species have appeared. Students should also understand that speciation increases the total number of species on Earth, and extinction decreases it. Students should also understand that gradual evolutionary change in a species is not speciation.
  

• A4.1.7

  Roles of reproductive isolation and differential selection in speciation

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  Include geographical isolation as a means of achieving reproductive isolation. Use the separation of bonobos and common chimpanzees by the Congo River as a specific example of divergence due to differential selection.
  

AHL Content Statements

• A4.1.8

  Differences and similarities between sympatric and allopatric speciation

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  Students should understand that reproductive isolation can be geographic, behavioural or temporal.
  

• A4.1.9

  Adaptive radiation as a source of biodiversity

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  Adaptive radiation allows closely related species to coexist without competing, thereby increasing biodiversity in ecosystems where there are vacant niches.
  

• A4.1.10

  Barriers to hybridization and sterility of interspecific hybrids as mechanisms for of preventing the mixing of alleles between species

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  Courtship behaviour often prevents hybridization in animal species. A mule is an example of a sterile hybrid.
  

• A4.1.11

  Abrupt speciation in plants by hybridization and polyploidy

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  Use knotweed or smartweed (genus Persicaria) as an example because it contains many species that have been formed by these processes.