Chapter 24: Evolution By Natural Selection
1. Define the term “evolution”.
- The idea that species change through time.
2. Why was Darwin’s book “On the Origin of Species” initially considered radical?
- His theory was inconsistent with the creation story in the Bible’s Book of Genesis; went against
prevailing scientific and world views held for centuries.
3. Briefly discuss the inheritance of acquired characteristics and identify its proponent.
- Individuals change as they develop in response to challenges posed by the environment, and
they pass on these phenotypic changes to offspring. For ex. Giraffes develop long necks as they
stretch to reach leaves high in treetops, and they then produce offspring with elongated necks
- Jean-Baptiste de Lemarck
4. Why is it wrong to say that “an individual evolves”?
- The population evolves, not the individual
5. Evolution operates upon what type of units?
6. Who was Alfred R. Wallace? How did Wallace influence Charles Darwin?
- Wallace independently formulated the theory of natural selection (evolution by natural
- He sent his article of natural selection to Darwin, who immediately recognised that they had
formulated the same explanation for how populations change through time. The two had their
papers read together and Darwin then rushed On The Origin of Species into publication a year
7. What was the “Evolutionary Turning Point”?
- Population genetics reconciled Mendelian genetics and Darwinian evolution
- An individual doesn’t evolve but populations do evolve
8. Discuss what is meant by “Modern Synthesis”.
- Genetic basis of variation and natural selection was examined
- Information from paleontology, taxonomy, biogeography, and population genetics emphasized
a. Populations are the units of evolution
b. Natural selection is the primary mechanism of evolutionary change
c. Gradualism – large changes result from the accumulation of small changes over long periods
9. Discuss the term “fitness” in Darwinian terms.
- The relative ability of an individual to produce viable offspring compared with other individuals
in the same population.
10. Discuss the term “adaptation”.
- A genetically coded trait (characteristic) that increases organism’s fitness, usually by helping the
organism to survive and reproduce in its natural environment; any heritable trait that increases
the fitness of an individual with that trait, compared with individuals without that trait, in a
particular environment 11. Discuss the sources of evidence, which support the theory of evolution. Include descriptive
examples to support your answer.
- Evidence for change through time: fossils found in sedimentary rocks
- Transitional forms: researchers found resemblances between the fossils found in rocks
underlying certain regions and the living species found in the same geographic areas; extinct
species in the fossil record were succeeded in the same region by similar species -> Darwin
pointed out that it provided strong evidence in favour of the hypothesis that species had
changed through time.
- Transitional forms document the changes that occurred as whales evolved from terrestrial
mammals to the aquatic mammals of today
12. Differentiate between the terms “ontogeny” and phylogeny”.
- Ontogeny: process of development of an individual organism; origin and development of an
individual organism from embryo to adult
- Phylogeny: evolutionary history of a species
13. What are vestigial structures? Describe examples of vestigial structures.
- Remnants of structures, which may be underdeveloped or seemingly useless
- Previously they may have had important functions in ancestors
- Examples in humans: chest hair, third molar, pointed canine
14. What are homologous structures? Discuss examples.
- Appear to have similar structural skeletal elements, but different functions
- Suggests support for a common ancestor
- For example, human hair and dog fur are homologous; humans have hair and dogs have hair
because they share a common ancestor that was a mammal and also had hair.
15. What are analogous structures? Discuss examples.
- Have similar functions, but found in animals that are not closely related
- These structures were not inherited from a common ancestor
- For example, wings of insects and wings of birds are both for a similar function – flight
- However, insect wings and bird wings are made of very different materials and are present in
more distantly related species
Chapter 25: Evolutionary Processes
1. Define the term “genetic drift” and “natural selection”.
- Natural selection increases the frequency of certain alleles – the ones that contribute to success
in survival and reproduction
- Genetic drift causes allele frequencies to change randomly. In some cases, drift may even cause
alleles that decrease fitness to increase in frequency.
2. State the Hardy-Weinberg equilibrium equation. Define each of the variables of the Hard-Weinberg
- Equation: p + 2pq + q = 12
- P is the frequency of the A1A1 genotype
- 2pq is the frequency of the A1A2 genotype - Q is the frequency of the A2A2 genotype
3. Discuss five conditions which must be satisfied for Hardy-Weinberg equilibrium. If a population
satisfies Hardy-Weinberg equilibrium, what may one conclude?
- 1. Population size is very large (low genetic drift)
- 2. No migration (population is isolated from other populations – low gene flow)
- 3. Mutations are rare and random (no net mutations)
- 4. Mating is random (maintaining random mixing of gametes)
- 5. No natural selection
- Allele and genotype frequencies within a population will remain constant from one generation
to the next as long as the conditions are met (no evolution will occur)
4. If a population does not satisfy the Hardy-Weinberg theorem, what may one conclude?
- If a population does not satisfy the theorem, then evolution is occurring. Nonrandom mating is
occurring, or allele frequencies are changing for some reason.
5. What can cause deviations from Hardy-Weinberg expectations?
- When non-random mating occurs, or allele frequencies are changing for some reason; or when
any of the five conditions are being violated.
6. Consider a population that is in Hardy-Weinberg equilibrium. The frequency of the allele ‘a’ is 0.3.
What is the percentage of the population that is heterozygous for this allele?
- p+q=1 p = .3 q = 1 - .3 = .7 2pq = 2(.7)(.3) = .42
7. Differentiate between stabilizing selection, directional selection, and disruptive selection. Use
labelled diagrams to support your answers. State an example for each of the three types of
- Stabilizing selection: selects against extreme phenotypes, favours intermediate variants,
reduces phenotypic variation with phenotypes suited to relatively stable environments
o Example: very small and very large babies are the most likely to die, leaving a narrower
distribution of birth weights
- Directional selection: favours one extreme, shifts frequency curve in one direction towards a
o Example: directional selection caused average body size to increase in a cliff swallow
population; larger birds survived because they had larger fat stores and did not get as
cold as the as the smaller birds
- Disruptive selection: opposite phenotype extremes are favoured over intermediate phenotypes
o Example: the bills of the black bellied seedcrackers; individuals with either very short or
very long beaks survive best. Only 2 sizes of seeds are available, big and small;
therefore, the intermediate beaks have trouble with both, so they are subject to
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8. Distinguish between intrasexual selection and intersexual selection.
- Intrasexual is male vs. male competition
o for ex. Male elephant seals fight for access to females (largest males do well)
- Intersexual is female choice
o Female long tailed widow birds choose males with the longest tails 9. Differentiate between the “bottleneck effect” and “the founder effect”.
- Bottleneck effect: presence of a bottlenecking event (natural disasters such as volcanoes,
earthquakes, floods, fires)
o As a result of the bottlenecking event the size of the population is reduced
o The surviving population is unlikely to represent the genetic composition of the original
- Founder effect: genetic drift in a new founder population (limited number of individuals) that
does not reflect the gene frequencies of the original (parent) population
o New founder population will be different
o When a group of individuals immigrates to a new geographic area and establishes a new
population founder event
10. Define “gene pool” and “gene flow”, and relate these terms to speciation.
- Gene pool: all of the alleles of all of the genes in a certain population