D4.1  Natural Selection

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.​

• What processes can cause changes in allele frequencies within a population?
• What is the role of reproduction in the process of natural selection?

​​
​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• How do intraspecific interactions differ from interspecific interactions? 
• What mechanisms minimize competition?

Resources:

• At SHS, Topic D4.1 is taught in the Natural Selection and Evolution of Gene Pools units. 
• Quizlet study set for this topic.  Coming soon!
• View the general sequence of the SHS course
• View the SHS units mapped to the IB Biology curriculum roadmap

D4.1.1— Natural selection as the mechanism driving evolutionary change.

• Define natural selection and fitness.
• Outline the process of natural selection and the resulting evolution of the population.
• Compare the reproductive success of better and less well-adapted individuals in a population.
• State that natural selection has operated continuously over billions of years, resulting in the biodiversity of life.
• Explain why Darwin’s evidence of evolution via natural selection resulted in a paradigm shift in the understanding of how life evolves.​

D4.1.2— Roles of mutation and sexual reproduction in generating the variation on which natural selection acts.

• Define biological variation.
• Explain why natural selection can only function if there is variation in a species.
• Outline sources of genetic variation (mutation, meiosis and sexual reproduction). 
• Compare variation that results from mutation to those that is generated from sexual reproduction.

D4.1.3-- Overproduction of offspring and competition for resources as factors that promote natural selection.

• State that species have the ability to produce more offspring than the environment can support.
• Use an example to illustrate the potential for overproduction of offspring in a population.
• Describe competition for resources as a consequence of overproduction of offspring.

D4.1.4--  Abiotic factors as selection pressures.

• Define selective pressure.
• Compare density-independent and density-dependent selective pressures.
• State example abiotic selective pressures.
• Outline how a selective pressure acts on the variation in a population.​

D4.1.5— Differences between individuals in adaptation, survival and reproduction as the basis for natural selection.  

• Define adaptation and fitness.
• Explain the effect of the selective pressure on the more and less adapted individuals in a population.
• Explain adaptation as a consequence of intraspecific competition. ​

D4.1.6- Requirement that traits are heritable for evolutionary change to occur.

• Explain why only heritable characteristics can be acted upon by natural selection.
  

 ​​​​D4.1.7- Sexual selection as a selection pressure in animal species.

• Outline the mechanism of sexual selection in evolution of courtship behavior and anatomical features. 
• Describe examples of sexual selection, including for color, size, and courtship behaviors.

D4.1.8- Modelling of sexual and natural selection based on experimental control of selection pressures.  

• Outline the selective pressures for and against coloration in guppies.
• Summarize John Endler’s experiments with guppies which demonstrate selection for and against coloration in different habitats.

AHL ​​​​​​​D4.1.9- Concept of the gene pool.

• Define gene pool, gene and allele.
• Describe how it is possible for multiple gene pools to exist in a single species.

AHL ​​​​​​​D4.1.10- Allele frequencies of geographically isolated populations.

• Define allele frequency.
• Calculate allele frequency from gene pool data. 
• Use a database to search for allele frequency of a human gene.​

AHL ​​​​​​​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.

• State that change in the allele frequencies of a gene is evidence of evolution.
• Explain how natural selection can lead to change in allele frequency in a gene pool. 
• Outline “neo-Darwinism” as the integration of genetic inheritance and the mechanism of natural selection.​

AHL ​​​​​​​D4.1.12- Differences between directional, disruptive and stabilizing selection.

• Outline the change in allele frequencies associated with stabilizing, disruptive and directional selection.
• Use graphs to illustrate or identify stabilizing, disruptive and directional selection.
• Outline an example of stabilizing, disruptive and directional selection.​

AHL ​​​​​​D4.1.13- Hardy–Weinberg equation and calculations of allele or genotype frequencies.

• State the Hardy-Weinberg equations.
• Given data, calculate allele frequencies of genes in a gene pool.
• Given data, calculate genotype frequencies of genes in a gene pool.​

AHL ​​​​​​D4.1.14- Hardy–Weinberg conditions that must be maintained for a population to be in genetic equilibrium.

• List the conditions under which populations maintain Hardy-Weinberg equilibrium.
• Explain how comparison of allele frequencies between two isolated populations of the same species can serve as evidence that divergence is (or is not) occurring).
• Explain how comparison of allele frequencies between one population at two points in time can serve as evidence that evolution is (or is not) occurring).​

AHL ​​​​​​D4.1.15- Artificial selection by deliberate choice of traits. 

• Define selective breeding and artificial selection.
• Outline the mechanism of artificial selection in evolution of crop plants and domestic animals,
• Describe an example of artificial selection of a crop plant or domestic animal.​