natural selection and evolution

• What is evolution?


  A gradual change in the inherited traits within a population over time
• What causes evolution to occur?

  It occurs due to natural selection
• What are the steps of the theory of natural selection?

  1. Genetic variation exists due to spontaneous mutations
  2. Selection pressures (e.g. competition, disease) exist
  3. Random mutation gives an organism a selective advantage
  4. Organism is better adapted to the environment and survives
  5. Organism reproduces, passing on its beneficial alleles
  6. Frequency of advantageous alleles increases
• Why does competition between organisms in a habitat exist?

  The resources within a habitat required for survival are limited
• What are some examples of competition between organisms within a habitat?

  • Competition between animals for food, shelter, mates, etc.
  • Competition between plants for light, water, minerals, etc.
• How does antibiotic resistance in bacteria illustrate the process of evolution?

  1. Genetic variation exists due to spontaneous mutations
  2. Antibiotics act as a selection pressure
  3. Mutations give a bacterium antibiotic-resistance
  4. If an antibiotic is administered, the bacterium survives while others are killed
  5. Bacterium reproduces, passing on its resistant variant
  6. Frequency of antibiotic-resistant allele increases
• Why is the development of antibiotic resistance in bacteria a good study for evolution?

  Bacteria reproduce very rapidly, allowing the first-hand observation of evolution
• How can the observation of fossils provide evidence for evolution?

  • Older fossils contain simpler organisms, while newer fossils contain more complex organisms
  • Fossils can be organized into chronological order, showing changes in organisms over time
• What was Darwin's role in the development of the theory of evolution by natural selection?

  • Studied a variety of organisms while traveling on the HMS Beagle
  • Noted that traits can be passed from parents to offspring
  • Proposed the idea of ‘survival of the fittest’
  • Established the theory of natural selection and published his ideas in ‘On the Origin of Species’
• What was Wallace's contribution to the theory of evolution by natural selection?

  • Proposed a theory of natural selection similar to Darwin’s, with different mechanisms
  • Gathered greater evidence (e.g. studying warning coloration in butterflies) to support the theory
• How has the theory of evolution by natural selection impacted modern biology and society?

  • Enables the classification of organisms into taxa
  • Influences modern medicine by emphasizing the importance of finishing antibiotic treatments
  • Highlights the importance of high genetic diversity in habitats for conservation projects
• What fossils have provided evidence for human evolution?

  • ‘Ardi’ - 4.4 million years old
  • ‘Lucy’ - 3.2 million years old
  • Leakey discovered 1.6 million year old fossils
• What clues does ‘Ardi’ give scientists about human evolution?

  • Female hominid fossil showing traits of both humans and apes:
  • Ape-like characteristics: long arms, large big toes
  • Human-like characteristics: structure of bones suggests upright walking
• What clues does ‘Lucy’ give scientists about human evolution?

  • Female hominid fossil showing more human-like traits than ‘Ardi’:
  • Structure of legs and feet adapted for walking
  • Brain size closer to that of an ape’s
• How did Leakey’s findings provide evidence for human evolution?

  • Discovered many hominid fossils
  • The 1.6 million year old fossil ‘Turkana Boy’ showed traits comparable to modern-day humans, e.g. similar brain size
• How has the development of stone tools provided evidence for evolution?

  • Correlation between the development of more complex tools and an increase in brain size
  • Primitive tools are older than more complex tools, indicating advancements in tool use as brain size increased
• What methods do scientists use to date tools?

  • Carbon-14 dating: estimating the age of carbon-containing material found in tools
  • Stratigraphy: using the age of sediment layers surrounding the tool as an indication of its age
• What is a pentadactyl limb?

  A limb with five digits present in animals, birds, reptiles, and amphibians
• How does the pentadactyl limb provide evidence for evolution?

  The presence of the pentadactyl limb suggests that all species with it have descended from a common ancestor
• What is classification?

  The organisation of organisms into groups
• What is taxonomy?

  The classification of organisms into taxa: kingdom, phylum, class, order, family, genus, species
• Name the five kingdoms.

  Animals, plants, fungi, protists, prokaryotes
• What happens to the number of organisms in each taxon as you move down the hierarchy?

  The number of organisms in each taxon group decreases
• What is the problem with grouping organisms based on similarities and differences in their anatomy and behavior?


  • Organisms that are not closely related may look alike (e.g., sharks and dolphins)
  • Closely related species may look very different (e.g., queen ants and worker ants)
• What advancements in science have led scientists to reconsider the five kingdoms classification system?

  • Microscopes
  • Biochemistry
  • DNA and RNA analysis
• Describe the three domains system of classification.

  • Organisms are divided into three groups: Archaea, Bacteria, Eukarya
  • Classification hierarchy: domain, kingdom, phylum, class, order, family, genus, species
• Which domain do eukaryotic organisms belong to?

  Eukarya
• Which domains do prokaryotic organisms belong to?

  Archaea and Bacteria
• Describe the domain Bacteria.

  Consists of true bacteria e.g. E.coli
• Describe the domain Archaea.


  • Consists of primitive microorganisms
  • Contains extremophiles adapted to live in extreme conditions (e.g., hot springs)
• What is selective breeding?

  The process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes.
• What are the main steps involved in selective breeding?

  1. Identify a desired characteristic (e.g., disease resistance).
  2. Select parent organisms that show the desired traits and breed them together.
  3. Select offspring with the desired traits and breed them together.
  4. Repeat the process until all offspring have the desired traits.
• What is the main advantage of selective breeding?

  It creates organisms with desirable features such as higher crop yields and increased milk production.
• Where else is selective breeding useful other than in agriculture?

  • In medical research
  • In sports (e.g., horse racing)
• What are the disadvantages of selective breeding?


  • Reduction in the gene pool, which can be harmful if sudden environmental changes occur.
  • Inbreeding can result in genetic disorders.
  • Development of physical problems (e.g., respiratory issues in bulldogs).
  • Potential to unknowingly select harmful recessive alleles.
• How can plants be cloned?

  • Taking plant cuttings
  • Tissue culture
• What is tissue culture?


  A method of growing living tissue in a suitable medium.
• Describe how plants are grown using tissue culture.

  1. Select a plant that shows desired characteristics.
  2. Cut multiple small sample pieces from meristem tissue.
  3. Grow in a petri dish containing growth medium.
  4. Transfer to compost for further growth.
• What must be ensured when preparing tissue cultures?

  Aseptic conditions must be ensured to prevent contamination by microorganisms.
• What does the growth medium contain?

  Nutrients and growth hormones.