SB13U-C UNIT 1 – KEY QUESTIONS
Lesson 1 – Origins of Evolutionary Theory
1. What wat the original purpose of Darwin’s voyage on the HMS Beagle and what was the
ultimate significance of the voyage? (2 marks)
The stated intent of the voyage was to obtain evidence to support the biblical theory of
creation and to chart the South American coastline. Darwin’s job was to observe, record
and collect specimens of rocks, minerals, plants, and animals. The ultimate
significance of the voyage is that it was instrumental in proving the theory of
evolution.
2. Why does the antibiotic resistance problem present an example of evolution? (3 marks)
The antibiotic resistance problem shows that when the environment of organisms such as
bacteria changes, the weaker ones die off and the stronger ones take over and multiply
(natural selection). When the stronger ones adapt to the new environment, they become
very successful at surviving harsher conditions, in this case, antibiotics. The stronger
bacteria thus evolve to become superbugs which are very difficult to eradicate.
3. Using the material covered in this lesson, and your own research, describe how the work
of Charles Lyell impacted the development of Charles Darwin’s theory of evolution.
Include the major work done by Lyell and what it led Darwin to consider. (8 marks)
Charles Lyell was an English geologist who wrote the book “Principles of Geology”.
Darwin read this book on the voyage aboard the HMS Beagle. There were two main
ideas proposed by Lyell that help influence Darwin’s theory of evolution. One was that
the earth was far older than originally thought and the other was that the geological
processes that gradually change the surface of the Earth was still occurring. While on the
voyage Darwin saw evidence that species changed over time and from place to place. He
also observed that after an earthquake the shoreline lifted three metres. This was further
confirmed by the discovery of fossilized sea creatures high up in the Andes. He began to
consider that maybe earth was much older that the 6000 years, especially after the
discovery of fossils of the giant Glyptodon and Megatherium which was thought to have
been extinct for 10, 000 years but was very similar to the modern-day armadillo. Darwin
wondered if, just like the Earth’s gradual changing over long period, species would
change gradually as well and also if environmental changes could impact the evolution of
species. Darwin realized that much of what Lyell wrote about was true and he used Lyell
kind of logic to develop his own ideas.
Lesson 2 – Natural Selection and Evidence for Evolution
4. What role does natural variation play in the process of natural selection and, ultimately
evolution? (3 marks)
If individuals within a population vary extensively in terms of size, shape, behaviour, and
more importantly reproductive abilities, the greater the chance for natural selection.
Natural variation will ensure individuals with beneficial traits that are better suited to
survive their environment will adapt faster and eventually reproduce and become the
larger population, while those with the less beneficial traits will eventually die off,
ultimately evolving the species into a more adapted society.
5. Give three lines of evidence that Darwin used to support his theory of evolution by
natural selection, and briefly explain how each one provided support. (6 marks: 2 marks
for each)
a) Fossils:
Darwin viewed fossils as detailed records of evolution. Fossils showed gradual
changes in form as one progressed through the strata. Older fossils found in
deeper layers were simpler in structure, whereas the ones found in upper layers
were more complex, proving how species can change over a long period of time.
b) Comparative Embryology:
Study of the early development of fertilized eggs shows that vertebrates embryos
develop through similar stages. Vertebrate embryos shared a basic genetic plan
for development they inherited from ancestors millions of years ago. The more
similar the embryonic stages, the more closely related the individuals eg. Calf
embryo closely resembles that of a hog. Embryos of fish, turtles, chicken, mice
and even humans develop tails and gills arches in early development which
showed they all share a common ancestor, some more distant than others.
c) Artificial Selection
Darwin observed how desired features were bred into domestic animals and plants
and how relatively fast the heritable changes occur, within a few thousand years.
He considered that if these selective traits can make such dramatic changes within
a few thousand years, then the evolution through natural selection given millions
of years would be even more dramatic
6. Imagine you are a farmer researching the impact of GMFs. What is one advantage and
one disadvantage that would be relevant to your work? Explain each. (4 marks)
As a farmer the advantage of disease resistance in GMF would be very relevant because
if crops can be made to fight off fungus, bacteria and viruses that would greatly reduce
the cost to producing crops. It would also limit how much pesticides that could enter the
environment. On the other hand, a GMF disadvantage that would really be concerning is
the issue of gene transfer to non-target species. The idea that invasive plants could
become superweeds by interbreeding with plants that can resist herbicides and pesticides
is alarming. This would mean that these superweeds could fight off natural enemies and
become even more impossible to eradicate, therefore, careful consideration must be taken
in the decision to use GMF.
7. Explain how natural selection could have produced the modern long-necked giraffe from
short-necked ancestors. (5 marks)
Natural selection produced long neck giraffe by the animal’s genotype for long neck.
Giraffes with natural variations including genes for short necks, short leg, short tongues
along with those with genes for longer necks, longer legs and longer tongues and any
other combination would have been in the original population. Eventually over a long
period of time the ones with shorter limbs which would prove an “injurious variation”
would die out because of their inability to reach food and those would longer limbs
would survive and successfully reproduce gradually making a combination of long necks,
legs and tongue to become the modern-day giraffe. The longer limbs and necks were
naturally selected by nature and in the words of Darwin “This preservation of favourable
variations and the rejection of injurious variations, I call Natural Selection”.
Lesson 3 – Evolutionary Mechanisms
(18 marks)
8. a)
Explain how genetic drift can lead to a reduction in the genetic variation within a
population. (3 marks)
Genetic drift can lead to reduced genetic variation within a population because
each subsequent reproduction from one generation to the next, results in offspring
with reduced traits or over represented traits from the original population.
Reduced traits are as a result of loss of alleles from a smaller gene pool which is
because of smaller population reproducing.
b)
Under what conditions is drift most likely to occur? (1 mark)
Drift is most likely to occur when there is a reduction in a population’s
ability to reproduce caused by either death of a large portion of the population or
disease limiting the population’s ability to reproduce.
c)
A flock of migrating birds is blown off course by a storm and carried towards a
small island that has no birds. Only three of the birds survive the storm and make
it to the island. They start to reproduce and, after several years, there are 500
birds on the island. Does the genetic variation in this population of birds result
from a population bottleneck or the founder effect? Explain. (2 marks)
The result is the founder effect because there is a new colony of birds on the
island started by only three birds (the founders). This population will have
reduced genetic variation from the original flock.
9. Describe the relationship between mutations, genetic variation and natural selection, and
evolution. Your description should include what a mutation is, which type of cells
mutations must occur in to increase genetic variations, and how variation is required for
natural selection. (4 marks)
Mutations are random changes that takes place in the genetic code or genotype of cells, it
occurs in both somatic and reproductive or sex cells. However, only mutations in sex
cells causes genetic variation as these cells are the only source of new alleles that pass on
traits from one generation to the next. Genetic variation and selection merely alter the
frequencies of existing genotype. The more mutations in the sex cells the more genetic
variations will be passed on to offspring.
Genetic variation produces individuals that are fittest to survive the environment by
natural selection. Natural selection means individuals with the best combination of
genetic variation will be favoured to survive and reproduce and those with injurious
variation will eventually die off. As the favoured individual reproduce and population
increases with more genetic variation, the population will evolve to become masters of
their environment, well adapted and that is evolution. Evolution is when mutation
increases the frequencies of different genotypes making a population change over a long
period of time to become well adapted to its environment and reproduce successfully.
10. Explain how natural selection and sexual selection can work together to cause the
evolution of large antlers on male moose. (4 marks)
Natural selection would have favoured the moose that is larger and with the largest
antlers to survive by being able to fight off predators and be more attractive to females,
for reproduction. Sexual attraction favours a trait that would encourage successful
mating. The female moose will be attracted to the larger males with larger antlers for
mating purposes. When they mate, they will produce males that are large and with larger
antlers as the gene will be passed on to the male offspring.
11. Suggest two ways a synthetic biologist can change the course of evolution. (4 marks: 2
marks for each)
Evolution is the process by which organisms change by mutation and adapt to its
environment to survive and successfully reproduce over a long period of time. Synthetic
biologists no longer need to wait for mutations to occur to make changes in cells.
Synthetic scientists are able to manipulate genes to do what ever they want, speeding up
processes that would take a long time, so they can speed up evolution. They can also use
their ability to manipulate genes to save lives by curing diseases, maybe even cancer, to
grow crops that are resistant to disease and pest and be more nutritious, and in general
increase and exponentially improve human lives.
Lesson 4 – Speciation
12.
Name the reproductive isolating mechanism operating in each situation below.
(5 marks: 1 mark for each)
a) One species of frog mates in April, but another mates in May.
Reproductive
Isolating
Mechanism
Temporal
b) Two fruit flies of different species produce sterile offspring.
Hybrid Sterility
c) The sperm of a marine worm penetrates eggs of the same
species only.
Gametic
d) One species of flower grows in forested areas, another in
meadows.
Habitat
e) Two species of pheasant perform different courtship dances.
Behavioural
Situation
13.
Describe the steps necessary for geographic isolation to lead to speciation. (4 marks)
First, a population needs to become isolated because of some physical barrier like an
ocean or desert. Then as many, many years go by, the separate smaller populations
become reproductively isolated and evolve separately into new species distinct from each
other, with the ability to successfully reproduce. Once new species evolve, this is
speciation and even if the isolated populations are re-introduced to each other by
removing the barriers, they will be unable to interbreed and successfully reproduce
because of how great the genetic differences evolve. Darwin’s finches are an example of
geographical isolation. A few finches came to the Galapagos from the south
American mainland and because of natural selection pressures, they evolved into
different species of birds on different islands adapting to their particular conditions on
each island.
14.
As a result of human activity (such as logging), large forests are becoming fragmented
into several smaller forests.
a) How might the increasing isolation of populations in these forests influence their
evolution? (3 marks)
Habitat isolation is most like to influence the evolution of forest that become
fragmented. As the forest breaks up the trees are more exposed to strong winds,
warmer temperatures, and less humidity which will affect the original
biodiversity. This can cause many species of trees and animals to die out and
become extinct. Each smaller sub-population will eventually evolve to adapt to
what ever environment they occupy to become different species, with trees being
unable to cross pollinate. Animals will be less likely to meet for mating, their food
source and type may change, and so selection pressures will force adaptations that
will cause species to evolve into different species. For the one that are favoured,
they will survive and reproduce and those with weaker fitness will die out.
b) How might the fragmentation affect the evolution of a large mammal, like a
moose, compared to a small invertebrate, like a worm? (2 marks)
When the forest is fragmented it becomes smaller with geographical barriers that
can separate the moose population. Selection pressures and restricted gene flow
may cause the moose to evolve into different organisms, some may even become
extinct. Smaller forest for large mammals may mean exposure, making them
easier game for hunting. The invertebrates, however, would most likely be
unaffected as they live in the earth and there will not be any barriers in the earth.
15.
Identify and explain the type of natural selection that accounts for the evolution of the
hollow bones of birds, which make flight possible. (4 marks)
Natural selection creates either a divergence or convergence of traits leading to the
change in population and possible speciation. Birds evolved from or diverged from traits
of larger organisms that were earthbound. Then selection towards or converged on traits
such as being smaller and having wings that would give them the ability to take flight to
escape predators. Directional selection favoured birds with the alleles for hollow bones
over solid as the hollow bones would make them lighter to fly easily. Directional
selection would keep pushing for the lighter, hollow bones, with the average dense bone
progressively trending towards hollow in subsequent generations, gradually evolving
birds into species that can fly efficiently.