VCE BIOLOGY – UNIT 4 – AOS 2 – OUTCOME 2 – SAC
EVOLUTIONARY THEORY AND RELATIONSHIPS
VCE Biology Study Design Links Outcome 2
On completion of this unit the student should be able to analyse and evaluate evidence for
evolutionary change and evolutionary relationships, and describe mechanisms for change including
the effect of human intervention on evolutionary processes.
School-Assessed Coursework Task
An oral or written report that demonstrates evolutionary relationships using first- or second-hand
data.
SAC PREPARATION
Prior to this task, define / explain the following terms and concepts. This must be completed before
attempting the SAC.
Adaptation
Niche
Adaptive Radiation
Recent Common Ancestor
Selective Pressures
Natural Selection
Evolution
Species
Speciation
Phylogenetic Tree
Microsatellites
Please read through the following article and investigate any terms that you do not understand. You
may also wish to research information relating to the SAC prior to completing it. You should be able
to provide two examples to demonstrate how Darwin and Lamarck explained ‘changes’ in an
organisms characteristics over time. Also ensure that you are comfortable in deciphering phylogenetic
trees.
SAC TASK
You will be provided with an article which examines the evolution of Galapagos finches in regards to
the research conducted by Charles Darwin. You will be given opportunities to research this paper
further prior to completing the SAC. You will then be given a series of questions to answer which will
assess your understanding of evolutionary processes in regards to this article and also your prior
research. You will have one period to complete this scaffolded written report.
Did Darwin get it wrong? Searching for the ancestor of Darwin's finches.
Article by Dr George Johnson.
Accessed from – http://go.hrw.com/resources/go_sc/bpe/HX10GJ13.PDF
Darwin first became convinced that evolution occurs when he collected a variety of small
birds on the Galapagos islands off the west coast of South America. All these birds proved to
be finches, a cluster of species closely related to one another and all resembling the finches of
the South American mainland. The simplest explanation, Darwin thought, was that a single
ancestor species of finch had migrated to the islands in the past, flying across the ocean from
South America. This one ancestral species then evolved into the 14 different species found on
the islands now. Darwin called this process "descent with modification" and regarded it as
key evidence for his theory of evolution by natural selection.
In the 140 years since, scientists have wondered about the identity of this ancestral species.
Did it come from South America, as Darwin proposed? The nearest point on the mainland is
Ecuador. To reach the Galapagos Islands from there, the ancestor of Darwin's finches would
have had to travel 900 km over the open ocean, a very long migration.
Using molecular data to test Darwin's hypothesis
There have been many attempts by scientists to confirm Darwin's hypothesis. Studies of the
birds' body shape and color are not conclusive, as differences are not distinctive. More recent
studies have focused on molecular data. A change in a protein or in DNA is like a unique
fingerprint, preserved from one generation to the next. Looking at these distinctive
differences, we should be able to see clearly who is related to who. But what molecular data
to use? You can't study variation among genes affecting proteins, mitochondrial DNA, or
nuclear DNA -- the 14 Galapagos finch species are so new (less than 3 million years old) that
too few protein or DNA differences have accumulated to make a reliable evolutionary tree.
A breakthrough in using molecular data to test the Darwin's proposal has been achieved this
year by examining variation in the length of microsatellite DNA sequences. Microsatellites
are highly-repeated gene sequences of a few thousand bases. Thousands of copies of them are
scattered about the chromosomes more or less at random. Microsatellite sequences have very
high mutation rates, and so are often used in DNA tests of paternity or for forensic
identification, as in the O J Simpson murder trial. Because of these very high mutation rates,
microsatellites would seem to be an ideal way to compare clusters of recently-formed species
such as Darwin's finches, as many DNA differences can be expected to have accumulated
even over a relatively short span of time. Evolutionary ecologist Ken Petren, with Peter and
Rosemary Grant of Princeton University, have examined 16 microsatellite markers on
genomic DNA drawn from the bird's blood. The markers show variation on exactly the
correct time scale to distinguish between the species.
What the molecular tree tells us
The evolutionary tree they obtained based on microsatellite length variation provides for the
first time a clear picture of the evolutionary history of Darwin's finches. In this tree,
horizontal branch lengths are proportional to genetics distance -- the longer the horizontal
line, the more different the DNA. Because their DNA is very similar, Geospiza scandens and
Geospiza conirostris share a branch line from other ground finches that is very short. Because
it's DNA is very different from the others, Certhidea olivacea shares a branch line with all the
other finches that is quite long.
Most importantly, the evolutionary tree obtained by this analysis of finch microsatellite DNA
is monophyletic. That is, all of the different Galapagos finches turn out to be descended from
a single ancestral form. At the base of the tree, the ancestor to all the other finches, is a
pointy-beaked warbler finch, Certhidea olivacea, with DNA very similar to warbler finches
on Ecuador, 900 km away. Darwin was right.
The subsequent evolutionary history of the 14 finch species can be clearly seen in the
microsatellite DNA tree. Galapagos finch evolution seems to have been driven largely by
diet. The long, pointy beaks of Warbler finches are generally associated with an insectivorous
diet. The first finches to reach the islands were insect eaters.
Two novel blunt-beaked forms evolved later, ground and tree finches, each opening up a new
ecological niche. In one innovation, the broad, stout beak of the Geospiza ground finch is
well suited for crushing seeds with the base of the beak. In the other innovation, the blunt
beak of the Camarhynchus tree finch focuses greater biting strength at the tip for tearing
vegetation.
Once these two novel beak shapes evolved, they each engendered a series of new species. In
these diverging species of Darwin's finches, the beak shapes remained relatively constant,
while body and beak size evolved to fill the new ecological niche. The microsatellite DNA
tree reveals these family relationships clearly. All the ground finches are more closely related
to each other than to any other finch. Similarly, all the tree finches prove to be more like each
other than like any other finch.
The DNA of the Galapagos finches contains preserved within it the traces of their
evolutionary history, a story which we have now learned to read.
VCE Biology – Unit 4 – AOS 2 – SAC TASK
“Did Darwin Get It Wrong? – The Finches of the Galapagos Islands”
Question 1. List and explain the factors which cause variation in a population?
(4 Marks)
Question 2. Describe the variations that exist within the populations of finches on the
Galapagos Islands?
(3 Marks)
Question 3. How can two or more species of finch co-exist without much competition in the
same habitat?
(3 Marks)
Question 4. Why is the large ground finch not in competition for food with the smaller
ground finch?
(2 Marks)
Question 5. Using dot points, describe the steps that might have lead to the evolution of
different finch species from an ancestral population on the Galapagos Islands?
(3 Marks)
Question 6. Describe the isolating mechanisms that need to be investigated to ensure that
the different populations are in fact distinct species. Include in your answer the
definition of a species.
(3 Marks)
Question 7. Using examples of your choosing, suggest how explanations from Charles
Darwin and Jean Baptiste Lamarck may have differed when linking variation,
natural selection and evolution?
(4 Marks)
Question 8.
(3 Marks)
Microsatellites are a recent development in evolutionary biotechnology.
Explain how this technology has provided evidence of evolutionary
relationships amongst species? Use the phylogenetic tree associated with the
article to support your answer.
GRADE
RANGE
1-5
6-10
11-15
16-20
21-25
DESCRIPTOR
Minimal reference to evolutionary theory. Includes some references to the aims
and methodologies of the investigation. Knowledge and understanding of data is
minimal, as are the identification and description of the practical investigation
procedures. Uses some terms and concepts related to evolutionary relationships
but a limited understanding is demonstrated.
Some understanding of evolutionary theory. Evidence of relevant discussion of
investigations aims and methodologies. Shows knowledge and understanding of
data, including the identification of correct procedures used throughout the
investigation. Some knowledge of evolutionary relationships terms and concepts
is demonstrated.
Mostly accurate understanding of evolutionary theory. Mostly accurate
explanation of the aims and methodologies of the investigation. Some detailed
analysis, evaluation and interpretation of the data provided. Identifies and
evaluates the procedures utilized during the practical investigation. Some
detailed knowledge provided concerning terminology, concepts and
understanding of evolutionary relationships.
Thorough understanding of evolutionary theory. Detailed examination and
understanding of aims and methodology. Detailed analysis, evaluation and
interpretation of data provided. Detailed evaluation of the practical investigation
procedures. Detailed knowledge of terminology and concepts associated with
evolutionary relationships.
Complex understanding of evolutionary theory. Very detailed understanding of
the aims and methodology of the investigation. Comprehensive analysis,
evaluation and interpretation of the data. A very well thought out and structured
evaluation of the practical investigation procedures. Comprehensive and detailed
knowledge of the terminology and concepts associated with evolutionary
relationships.
N.B. The descriptors have been adapted from the Victorian Curriculum and Assessment Authority guidelines.