SL Content Statements

• D4.1.1

  Natural selection as the mechanism driving evolutionary change
  

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  Students should appreciate that natural selection operates continuously and over billions of years, resulting in the biodiversity of life on Earth.
  NOS: In Darwin’s time it was widely understood that species evolved, but the mechanism was not clear. Darwin’s theory provided a convincing mechanism and replaced Lamarckism. This is an example of a paradigm shift. Students should understand the meaning of the term “paradigm shift”.
  

• D4.1.2

  Roles of mutation and sexual reproduction in generating the variation on which natural selection acts

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  Mutation generates new alleles and sexual reproduction generates new combinations of alleles.
  

• D4.1.3

  Overproduction of offspring and competition for resources as factors that promote natural selection

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  Include examples of food and other resources that may limit carrying capacity.
  

• D4.1.4

  Abiotic factors as selection pressures

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  Include examples of density-independent factors such as high or low temperatures that may affect survival of individuals in a population.
  

• D4.1.5

  Differences between individuals in adaptation, survival and reproduction as the basis for natural selection
  

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  Students are required to study natural selection due to intraspecific competition, including the concept of fitness when discussing the survival value and reproductive potential of a genotype.
  

• D4.1.6

  Requirement that traits are heritable for evolutionary change to occur
  

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  Students should understand that characteristics acquired during an individual’s life due to environmental factors are not encoded in the base sequence of genes and so are not heritable.
  

• D4.1.7

  Sexual selection as a selection pressure in animal species
  

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  Differences in physical and behavioural traits, which can be used as signs of overall fitness, can affect success in attracting a mate and so drive the evolution of an animal population. Illustrate this using suitable examples such as the evolution of the plumage of birds of paradise.
  

• D4.1.8

  Modelling of sexual and natural selection based on experimental control of selection pressures
  

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  AOS: Students should interpret data from John Endler’s experiments with guppies.
  

AHL Content Statements

• D4.1.9

  Concept of the gene pool
  

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  A gene pool consists of all the genes and their different alleles, present in a population.
  

• D4.1.10

  Allele frequencies of geographically isolated populations

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  AOS: Students should use databases to search allele frequencies. Use at least one human example.
  

• D4.1.11

  Changes in allele frequency in the gene pool as a consequence of natural selection between individuals according to differences in their heritable traits

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  Darwin developed the theory of evolution by natural selection. Biologists subsequently integrated genetics with natural selection in what is now known as neo-Darwinism.
  

• D4.1.12

  Differences between directional, disruptive and stabilizing selection

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  Students should be aware that all three types result in a change in allele frequency.
  

• D4.1.13

  Hardy–Weinberg equation and calculations of allele or genotype frequencies
  

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  Use p and q to denote the two allele frequencies. Students should understand that p + q = 1 so genotype frequencies are predicted by the Hardy–Weinberg equation: p 2 + 2pq + q 2 = 1.
  If one of the genotype frequencies is known, the allele frequencies can be calculated using the same equations.
  

• D4.1.14

  Hardy–Weinberg conditions that must be maintained for a population to be in genetic equilibrium

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  Students should understand that if genotype frequencies in a population do not fit the Hardy–Weinberg equation, this indicates that one or more of the conditions is not being met, for example mating is non- random or survival rates vary between genotypes.
  

• D4.1.15

  Artificial selection by deliberate choice of traits

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  Artificial selection is carried out in crop plants and domesticated animals by choosing individuals for breeding that have desirable traits. Unintended consequences of human actions, such as the evolution of resistance in bacteria when an antibiotic is used, are due to natural rather than artificial selection.