Natural Selection (IB Topic D4.1)

Essential Idea(s): Life evolves. Variations in genes result in variations in traits. Some of those traits end up giving certain organisms an advantage at survival. Environments change, too – so the ability to adapt and evolve is essential for life on earth.

Unit Length: 3 Lessons (+2 AHL)

  Guiding Questions

◊ What processes can cause changes in allele frequencies within a population?

◊ What is the role of reproduction in the process of natural selection?

Materials:

Self-Teaching Slides (SL) / Self-Teaching Slides (AHL) Quizlet Vocab Set
Notes Template (SL) / Notes Template (AHL)

 

IB Statement(s) and Objective(s)

 

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

  • Define natural selection
  • Outline Lamarckism as a mechanism to explain evolution
  • Contrast Darwinism (natural selection) with Lamarckism
  • Explain the concept of natural selection as a mechanism for evolutionary change
  • NOS: Outline the theory of evolution by natural selection as an example of the correspondence, coherence and pragmatic theories of truth

 

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

  • Explain why natural selection can only function if there is variation in a species
  • Outline genetic mutations as a source of genetic variation
  • Outline meiosis as a source of genetic variation
  • Outline sexual reproduction as a source of genetic variation
  • Outline gene flow as a source of genetic variation

 

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

  • Use an example to illustrate the potential for overproduction of offspring in a population
  • State two evolutionary benefits of overproduction of offspring
  • Describe competition for resources as a consequence of overproduction of offspring
  • Explain the Darwinian concept of “survival of the fittest”
  • List examples of resources that may limit population size

 

D4.1.4: Abiotic factors as selection pressures

  • Define selective pressure
  • Compare density-dependent to density-independent selection pressures
  • State that abiotic selection pressures are typically density independent

 

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 natural selection

 

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

  • Distinguish between heritable and acquired characteristics
  • Explain why only heritable characteristics can be acted upon by natural selection

 

D4.1.7: Sexual selection as a selection pressure in animal species

  • Define sexual selection
  • 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

  • NOS Concept: Explain what models are and their purposes in science
  • Summarize John Endler’s experiments with guppies which demonstrate selection for and against coloration in different habitats

Additional Higher Level Topics

D4.1.9: Concept of the gene pool

  • Define gene pool
  • Describe how it is possible for multiple gene pools to exist in a single species
  • Define gene flow
  • Outline the effects of gene flow on genetic diversity

 

D4.1.10: Allele frequencies of geographically isolated populations

  • Define allele frequency
  • Outline how to calculate allele frequencies
  • Use a database to search for allele frequency of a human gene

 

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

  • Define “neo-Darwinism”
  • State that change in the allele frequencies of a gene is evidence of evolution
  • List processes that can change allele frequency in a population
  • Outline mutation / gene-flow / non-random mating / genetic drift and/or selection as mechanisms that can cause change to allele frequencies  

 

D4.1.12: Differences between directional, disruptive and stabilizing selection

  • Outline the change in allele frequencies associated with stabilizing, disruptive and directional selection
  • Give an example each of stabilizing, disruptive, and directional selection

 

D4.1.13: Hardy–Weinberg equation and calculations of allele or genotype frequencies

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

  • State the Hardy-Weinberg equation and outline its use in ecological investigations 
  • Explain how the Hardy-Weinberg equation can be used to infer the presence of evolutionary forces for a specific trait in a population
  • Given data, calculate allele frequencies of genes in a gene pool
  • Outline conditions necessary for the Hardy-Weinberg equation to be at equilibrium

 

D4.1.15: Artificial selection by deliberate choice of traits

  • Define artificial selection
  • Use an example to explain how selective breeding has led to evolution in a species
  • Explain the process of artificial selection using selective breeding
Activities: ⓟ = podcast / ⍰ = inquiry 5 / ⓦ = Write it /  Ӕ = The academy  / Ⓡ = Read it

ⓟ/ⓦ: Fox Farm – The Experiment to Turn Wild Foxes into Domesticated Pets (👫 max 3)

Starting in the 1960s, Russian geneticist Dmitry Belyaev started an experiment to see how many generations it would take to turn wild foxes into loveable, cuddly domesticated pets – just like dogs. It happened surprisingly quickly. Watch this video to learn about the experiment, and discuss: 1) How and why natural selection created the fearful and aggressive foxes found in the wild; and 2) how the process of artificial selection worked in Belyaev’s fox population. Make sure you mention genes, and the potential to select for both tame and aggressive foxes. 

 

ⓟ/ⓦ: Far from Perfect – When Evolution Isn’t So Impressive (👫 max 3)

Biology teachers and hippies alike both love to talk about the perfection of the human body. In reality, nature can be pretty sloppy. Just look at us: humans breathe and eat with the same tube – which enables choking. Until recently, humans died during childbirth more often (and experienced more pain) than almost any other animal – a result of narrowed hips from evolving to walk on two legs. Human knees, for whatever reason, only move in 2 directions, making knee injuries all too common and painful. Read the article, and highlight some of evolution’s greatest foul-ups in humans. In doing so, explain how evolution does not “give organisms what they need,” but instead is a random and selective process.

 

Ⓛ (Simulation): Hawks vs. Mice (👫 max 2)

Play with this simulation so that you feel confident in how it works. Record a screencast of the simulation in action, explaining the key steps of Natural Selection as you go (cover all of the ICE AGE components). Make sure you also explore the alleles of the mice populations — show how one allele becomes the most frequent, depending on the beach vs. field environment.  

 

Ⓛ (Simulation): What Happens if They All Survive? (👫 max 2)

What happens when all the offspring of a species survive, AND there are unlimited resources? Explore the concepts of carrying capacity, exponential growth and logistical growth with this simulation task. Complete the attached worksheet using the website linked within.

 

Ⓛ (Simulation): The Rabbits vs. the Wolves (👫 max 2)

Play with this simulation until you are confident with how it works. Then, complete this accompanying worksheet. Make sure you track all the data and thoroughly answer the questions at the end. 

 

Ⓛ (Simulation): Modeling Darwin’s Finches (👫 max 2)

To begin, print out this sheet (or ask me to) – you will use the (+) and (-) as representations of alleles within a finch population. See how they evolve when you simulate a change in the environment. Follow the instructions to complete the lab and answer all accompanying questions.

 

ⓟ (or role play): Misconception City (👫 max 3)

“Evolution is just a theory.” “We evolved from apes.” “Evolution can’t explain complex organs”. “Evolution can’t be proven.” 

There are dozens of misconceptions about evolution, especially among groups of people that have been actively taught against it. Together with a partner, make a podcast/vlog to debunk the top misconceptions about evolution provided in the link. Choose enough to explain all of the elements of ICE AGE.

 

ⓟ/ⓦ: The Antibiotic Apocalypse (👫 max 2)

The discovery of antibiotics saved hundreds of millions of lives in the 20th century. Unfortunately, their widespread use is also the root of their demise – more and more bacteria are evolving into “superbugs” that are resistant to all of our antibiotic treatments. It will only get worse with time. Watch this quality Kurzgesagt video on antibiotics, then use VISTA to explain how superbugs evolved alongside our overuse of antibiotics, and what can be done about this dark side of evolution.

 

📄: Out of the Ashes: The Dawn of Mammals (💁)

The violent meteor impact 65 million years ago was a bad thing for dinosaurs – it marked the end of their very long dominance of Earth. It was – fortunately for us – a very good thing for the future of mammals. Watch this 15-minute video to find out how mammals became the dominant creatures following the impact, and complete this accompanying worksheet.

 

Ӕ: The Academy – Natural Selection (💁)

Although students feel like they understand natural selection quite easily, they often find it quite difficult to explain clearly when speaking or writing. Create a Khan-academy style video to help address this (go here for inspiration). Explain natural selection and the steps summarized in ICE AGE, using examples of specific species.