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YEAR 12 BIOLOGY
1.
LESSON 1: EVOLUTION
History of Evolution
Students learn to:


Analyse information from secondary sources on the historical development of theories of evolution
and use available evidence to assess social and political influences on these developments.
Quick Review of Evolution

In a very broad sense, evolution simply means ‘change over time’.
However, this is not a very good working definition for purposes of Biology.

This is because many processes in nature involve ‘change over time’,
yet we would not classify them as ‘evolution’. Can you think of any
examples?1
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
A better, but still very simple, definition of biological evolution is descent
with modification.

This involves heritable changes to the gene pool that are passed on
when an organism reproduces.

Over time, these changes accumulate and can quite drastically alter
the morphology, physiology, and behaviour of an entire species.

This brings us to modern evolutionary theory which holds that all organisms
descended from a single common ancestor.

This means that all organisms are related, if very distantly in some
cases.

This concept is often referred to as the ‘Tree of Life’.
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YEAR 12 BIOLOGY
LESSON 1: EVOLUTION
Source: http://tbi.montana.edu/outreach/hotscience/materials/

Recall that the three main branches above are the three ‘Domains’ of life.

All three of them can then be categorised as consisting of one of two
types of cells: prokaryotic cells or eukaryotic cells.

Can you remember the difference between these types of cells?2
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
In the diagram above, where would the common ancestor be? Label it in
the appropriate place on the tree.3

Watch a VIDEO (Length 6:29) about the Tree of Life (David Attenborough).

When is life first thought to have begun? What kind of cell would it likely
have been?4
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
16th Century

Andreas Vesalius

Vesalius was an anatomist born in the Netherlands who sought to
understand the world through careful observation.

He noticed and documented many similarities between various
organisms, and made special note of the extensive list of physical
features that humans have in common with many other animals.
Source: http://warforscience.wordpress.com/2009/12/20/answering-creationist-claims-part-2awe-dont-jumble-fossils-together/
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
17th Century

Nicolas Steno

Steno was an anatomist from Denmark. He was the first scientist to
realise and document the importance of fossils.

He believed that fossils were the preserved remains of ancient
organisms, and could actually tell us something significant about the
evolution of past life on earth.
Source: http://science.nationalgeographic.com/wallpaper/science/photos/permian-period/trilobite-fossil/
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
18th Century

Karl von Linné

Swedish botanist Karl von Linné (also known as Linnaeus) noted that
plant hybrids could be created by cross pollination.

Although such pollination produced varieties that had not existed before,
he distinguished this process from the process of evolution.

What is Linnaeus famous for? (Hint: think back to Year 11)5
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Source: http://www.nma.gov.au/collections/collection_interactives/european_voyages/

Erasmus Darwin

Erasmus Darwin was the Grandfather of Charles Darwin.

He was a well-respected English scientist who wrote poems
suggesting that evolution had occurred in living organisms, including
humans.

However, he did not propose any mechanism for how evolution could
occur.

Why do you think Erasmus Darwin did not publish his ideas openly?6
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
19th Century

Jean Baptiste Lamarck

Lamarck was a French naturalist who made important early
contributions to evolutionary theory.

He believed that adaptations were developed by individual organisms
based on inner ‘need’, becoming acquired characteristics which were
passed on to offspring directly.

For example, Lamarck thought that giraffes’ necks became longer
between generations if parent giraffes had to stretch their neck further
to reach higher leaves on trees.
Source: http://sabrinafair2.tripod.com/evolutionproject/id9.html

Based on Lamarckian theory, describe what your offspring would look
like if you went to the gym every day and became a bodybuilder.7
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
Generally speaking, Lamarck’s theory has been proven to be incorrect
and has been largely replaced by Darwin’s theory.

However, scientists have recently found a few examples of evolutionary
processes that seem to somewhat support Lamarck’s theory. An
example of this is the new field called ‘Epigenetics’. If interested, you
can watch this brief VIDEO (Length 1:47).

Charles Robert Darwin

Darwin was an English naturalist with an intense passion for studying
the natural world.

Darwin developed his ideas and gathered evidence while aboard the
H.M.S. Beagle on a British science expedition around the world.

In South America, Darwin found fossils of extinct animals that were
similar to modern species. On the Galapagos Islands he noticed
many variations among plants and animals of the same general type
as those in South America.

His real legacy was not proposing the idea of evolution; that was old
news.

Darwin’s real breakthrough came in proposing a mechanism for
evolution: the process of natural selection.
Source: http://beforeitsnews.com/science-and-technology/2012/03/darwins-h-index-1847177.html
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
Upon his return to London, Darwin theorised that:
a)
gradual change over time did occur
b)
evolutionary change was very slow, requiring thousands to millions of
years
c)
variation in a species occurs randomly
d)
the survival of each organism is due to its ability to cope in a
changing environment i.e. the primary mechanism for evolution was
natural selection
e)
the millions of species alive today all arose from a single original life
form through a branching process called speciation

In 1859, Darwin wrote his famous book called On the Origin of Species.

Watch a short VIDEO (Length 3:37) on Darwin. How do you think
society and politics affected the development of the theory of evolution
over time?8
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
Watch this VIDEO (Length 4:25) of the Huxley-Wilberforce debate in
1860 which highlights the social and political reactions to Darwin’s
theory of evolution in the 19th Century.
Source: http://www.mun.ca/biology/scarr/Mans_Place_in_Nature.html
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
Alfred Russel Wallace

Wallace was a British naturalist who postulated, independently from
Darwin, the theory of evolution by natural selection.

In 1858, Wallace actually sent Darwin a draft of his ideas, and Darwin
was quite shocked to see that they were virtually identical to his own.

Darwin and Wallace then arranged to present a joint paper together to
the Linnaean Society later that year outlining their ideas.

Wallace went on to later focus on biogeography, while Darwin published
a much larger version of their joint paper: On the Origin of Species.
Source: http://www.theguardian.com/science/2013/aug/09/charles-darwin-alfred-russel-wallace
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YEAR 12 BIOLOGY
LESSON 1: EVOLUTION
Summarise in the following table the ideas of various scientists regarding evolution.9
Date
Theorist/Scientist
16th Century
Andreas Vesalius
17th Century
Nicolas Steno
18th Century
Karl von Linné
18th Century
Erasmus Darwin
19th Century
Jean Baptiste Lamarck
19th Century
Charles Darwin
19th Century
Alfred Wallace
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YEAR 12 BIOLOGY
LESSON 1: EVOLUTION
2.
Wallace-Darwinian Evolution

Darwinian Theory of Evolution

The Darwinian Theory of Evolution proposes that evolution occurs as a
function of “survival of the fittest”.

How do you think we measure fitness though? What would be the
single most important factor for scientists in determining if an organism
is ‘fit’?10
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
This theory states that:

More offspring are produced than can survive in a population, and, as
population size tends to remain relatively constant, many offspring
must die.
Source: http://evolution.berkeley.edu/evolibrary/article/evo_25

Thus, there is a struggle for existence where the better-adapted
individuals will survive so that they have the opportunity to reproduce
and pass on their genes to their offspring.
Source: http://evolution.berkeley.edu/evolibrary/article/evo_25
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
Over long periods of time (remember, life is thought to be 3.5 billion
years old!), the more suited adaptations or favourable traits of
individuals will become prevalent in the population.
Source: http://evolution.berkeley.edu/evolibrary/article/evo_25

Gradually, as new adaptations accumulate, the population will become
very different – maybe even with new species.
How would you be able to tell if the changed population was a new
species?11
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Note to Students

Be very careful when answering evolution questions. Your answer can NEVER
sound Lamarckian, or you won’t gain the marks.

Things which may sound Lamarckian include saying that an organism changes over
time (instead of a population of organisms changes over time) and that organisms
‘adapt’ to their environment (species can change over generations to possess
adaptations which help to ensure survival, but individual organisms do not ‘adapt’
as adaptations have a genetic basis).

An alternative way to convey these ideas is stating that organisms possess
‘favourable traits’ or ‘favourable characteristics’ that help to ensure survival.
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
The following flow-chart should be used when answering questions on
evolution.
VARIATION in population
SELECTION PRESSURE
DEATH of poorly adapted
organisms (with
unfavourable
characteristics)
SURVIVAL of well-adapted
organisms (with favourabe
characteristics)
REPRODUCTION - passing
on the favourable
characteristics to offspring
DOMINANCE - majority of
the population contains the
favourable characteristics
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YEAR 12 BIOLOGY
LESSON 1: EVOLUTION
[CSSA 2008 Q21]
Whales have an external covering that contains a thick layer of fat called blubber. Scientists
have noted that whales living in colder waters have thicker blubber than those in the warmer
tropical waters.
Explain how an increase in the water temperature due to global warming may affect the
evolution of whales in the long term.12
3


Criteria
Identifies there is variation in a population and that an environment
selection pressure exists.
Describes the process of natural selection whereby organisms with suitable
characteristics survive and pass on their traits.
Describes the increase in prevalence of this characteristic over time.
Any TWO of the above.

Only ONE of the above.


Marks
3
2
1
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YEAR 12 BIOLOGY
LESSON 1: EVOLUTION
3.
Origin of Life VS Origin of Species

Evolution versus Abiogenesis

Evolution is the theory which explains how species evolve over time.

It is not a theory which explains the origins of life.

This is a common misconception both among scientist and theologians
in the ongoing debate of creation versus evolution.

Recall that abiogenesis is the idea that life could have originated from
inorganic molecules.

The origin of life remains a very problematic field of research, and is far
from being a settled theory.
Source: http://evolution.berkeley.edu/evosite/evo101/IIE2bStudyorigins.shtml
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YEAR 12 BIOLOGY
4.
LESSON 1: EVOLUTION
First-Hand Investigation: Modelling Evolution
Students learn to:
 Plan, choose equipment or resources and perform a first-hand investigation to model natural
selection

Introduction

What is the basis on which natural selection works?13
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
How can environments change?14
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
What happens to some organisms when there is a change in the
environment?15
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
What do all organisms do to continue their species?16
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
How do the organisms which reproduce affect their offspring?17
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
Over time and many generations, what happens to the population of
organisms?18
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
If one part of the population is cut off from the rest, they may evolve in
different directions until they can no longer reproduce and produce fertile
offspring. What is this called?19
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
You may use this SIMULATION to model natural selection and help clarify
the process a bit more. Alternatively, you may proceed to the jellybean
model on the following pages.
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
The Jellybean Model of Evolution
Source: http://beckyandthebeanstock.com/wp-content/uploads/2008/03/jellybeans4.jpg

Introduction: The jellybean model uses the idea of predators (humans) and
prey (jellybeans).

Aim: To model evolution by natural selection.

Method

Each student in a group is given a different implement, e.g. a fork, a
spoon, a knife, a single chopstick, or a skewer.

A bag of jellybeans is spilled onto the floor.

Each student has 30 seconds to use their implement to obtain as many
jellybeans as possible.

At the end of the 30 seconds, each student counts the number of
jellybeans they collected.

At the end of each round, the student who collected the least number of
jellybeans is removed from the game.

After many rounds, only the person with the most effectively-shaped
implement for collecting jellybeans should be left.
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
Results and Discussion

What do the different implements represent in the model?20
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
What do the jelly beans model?21
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
What does removing one player/implement from the game each round
model?22
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
What do the rounds model?23
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
What does the final result model?24
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
What important part of evolution is NOT shown in this model?25
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YEAR 12 BIOLOGY
LESSON 1: EVOLUTION
[HSC 2003 Q25]
You have carried out first-hand investigations that have attempted to model biological
concepts.
Discuss the use and limitations of models when illustrating biological concepts.26









Criteria
Identifies at least TWO limitations in using model(s).
Provides TWO reasons for the use of model(s).
4
Marks
4
Identifies TWO limitations and provides one reason for using model(s).
OR
Provides TWO reasons for using models and one against.
Identifies ONE limitation but has made one point for use of model(s).
OR
Identifies TWO limitations in using model(s).
OR
Provides TWOpoints for using model(s).
Identifies ONE limitation.
OR
ONE point for use.
3
2
1
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YEAR 12 BIOLOGY
5.
LESSON 1: EVOLUTION
Divergent and Convergent Evolution
Students learn to:


Explain how Darwin/Wallace’s theory of evolution by natural selection and isolation accounts for
divergent evolution and convergent evolution.
What is a ‘Species’?

The word ‘species’ gets thrown around quite a lot, but surprisingly it is often
misunderstood. See if you can write a definition for species below:27
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
Determination of a species strictly on something like appearance can be
quite problematic.

The butterflies below undergo drastic seasonal changes that could be
easily mistaken for separate species.
Source: http://www.nature.com/scitable/content/variation-within-species-4308521

Within the same species, individual organisms can look quite different.
For these three species of butterflies, wing colour and pattern varies
depending on the season during which they were born.

The butterflies at the top were born under different temperature and
light conditions than the ones at the bottom.
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
Alternatively, distinct species can look quite similar or even almost identical,
yet they are classified as separate species such as the Meadowlarks below.
Source: http://www.nature.com/scitable/content/western-meadowlark-and-easternmeadowlark-two-distinct-4257520

Even though they look similar and have overlapping ranges, the
western meadowlark (left), and the eastern meadowlark (right), have
distinctly different songs.

As a result, they do not interbreed and are classified as separate
species.

So why does all this detailed information about a ‘species’ matter? Recall
that Darwin’s 1859 publication was called On the Origin of Species.28
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
You need understand two important processes that are often discussed
when mentioning species:
(i)
Divergent evolution and;
(ii)
Convergent evolution.
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
Divergent Evolution

Divergent evolution is the process where two or more related species
become less similar – that is, they diverge.

It can develop to the point where one species slowly evolves over time
into two (or more) different species.

The process of forming a new species is known as speciation.

Speciation can occur by two basic mechanisms:
(i)
Allopatric speciation and;
(ii)
Sympatric speciation.
Source:
http://science.kennesaw.edu/~jdirnber/Bio2108/Lecture/LecEvolution/Evol4MacroEvol.html

From the diagram, what appears to be the main difference between
allopatric and sympatric speciation?29
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
Allopatric Speciation: an ancestral species becomes physically or
geographically separated and each group evolves independently of the
other, leading to separate species.

Example: Californian salamanders have been separated and
reproductively isolated in different rivers resulting in separate species.
Source: http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ev/m3/s2/evm3s2_4.htm

What environmental changes or factors (other than those in the picture
above) can isolate a small group or divide a population?30
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
Sympatric Speciation: an ancestral species evolves into two separate
species within the same physical or geographical location due to slight
behavioural modifications (e.g. selection of a new food source by a group
of individuals).

Example: Cichlids in Lake Victoria, East Africa have evolved into
separate species within the same lake by specialising on different foods.
Source: http://faculty.southwest.tn.edu/rburkett/GB%20Properties%20of%20Life.htm

What other factors could drive sympatric speciation other than specialised
on certain food sources?31
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
If this process of divergent evolution continues to the extent of creating a
number of distinct species from a single common ancestor, the process
is referred to as adaptive radiation.

The ancestral species have been subjected to divergent evolutionary
mechanisms a number of times and each new species has ‘adapted’
and ‘radiated’ out to fill specific ecological niches (e.g. eating from
specific food sources).

Darwin’s Galapagos finches are the prime example.
Source: http://mayhewbiology.com/Biology%20notes/speciation%20notes.htm

Watch a VIDEO (Length 2:09) on Darwin’s finches.

What do you suppose was the primary mechanism (allopatric or
sympatric speciation) in the formation of so many different finch
species?32
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YEAR 12 BIOLOGY
LESSON 1: EVOLUTION
Explain how the different finch species evolved.33
3
Note to Students
Recall that when answering questions on evolution, you MUST always include:
1. Variation within the population
2. Selection pressure causes the survival of some with the beneficial characteristics,
death of others without replacing it
3. Reproducing
4. Passing on the characteristics to the next generation
5. Over long periods of time/many generations
6. Population develops to mostly contain the beneficial characteristic
Most students forget to talk about variation within the population or that evolution occurs
over long periods of time.
Criteria
Clearly relates cause and effect of evolution by natural selection of Darwin’s
finches using all SIX key points above.
Marks
3

Relates cause and effect of evolution by natural selection of Darwin’s finches
including THREE to FOUR key points above.
2

Identifies some link between cause and effects of evolution by natural
selection of Darwin’s finches using only ONE to TWO key points above.
1

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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
Convergent Evolution

Convergent evolution is the process by which unrelated (or only distantly
related) organisms evolve to become more similar in some regard (e.g.
body form, colour, behaviour, organs, etc.).

This is caused by the unrelated organisms being subjected to similar
environmental conditions or ecological niches.

A classic example of convergent evolution is the presence of wings in
bats, birds, and insects.
Source: http://archive.peabody.yale.edu/exhibits/treeoflife/convergent.html

These organisms are only very distantly related as their last ‘common
ancestor’ would have been a very simple multicellular organism from
many hundreds of millions of years ago WITHOUT any wings.

This means the wings have arisen independently in each group of
organisms (bats, birds, and insects) due to environmental conditions,
allowing them to exhibit similar behaviours (flying).
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
PLEASE NOTE: Convergent evolution does NOT state that the organisms
are evolving into one another – bats are not slowly becoming birds or even
more ‘bird-like’.

Convergent evolution simply states that birds and bats have developed
a similar trait (wings) and behaviour (flying) as a response to similar
environmental conditions and to fill specific ecological niches.

Another good example of convergent evolution is the long list of similarities
between various marsupial and placental mammals. See the table below.

These mammals are similar in body form as well as habitat
requirements.
Source: http://home.comcast.net/~mjmayhew42/Biology%20notes/patterns%20notes.htm
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YEAR 12 BIOLOGY

LESSON 1: EVOLUTION
Watch VIDEO 1 (Length 3:05) and VIDEO 2 (Length 2:26) about
convergent evolution and answer the following questions.

What factors were driving the process of evolution in the various
organisms discussed in the first video?34
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
What about the Mako Shark in the second video?35
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YEAR 12 BIOLOGY
LESSON 1: EVOLUTION
Complete the following table:36
Type of
Examples
Description
Evolution
Divergent
Convergent
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YEAR 12 BIOLOGY
LESSON 1: EVOLUTION
[HSC 2004 Q18]
A plant species found in the area immediately around Sydney has also been found in a small
area in the Gibraltar Range in the far north of NSW.
Predict what might happen to the TWO populations over the next 5 million years, in terms of
Darwin/Wallace’s theory of evolution.37
3
Criteria
• Makes a valid prediction for BOTH populations in terms of Darwin/Wallace Theory
of Evolution
Marks
3
• Makes a valid prediction for ONE population in terms of Darwin/Wallace Theory of
Evolution
2
• Makes one valid prediction without making reference to Darwin/Wallace Theory of
Evolution
OR
• Provides correct information about Darwin/Wallace Theory of Evolution without
making a prediction
1
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YEAR 12 BIOLOGY
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LESSON 1: EVOLUTION
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YEAR 12 BIOLOGY
LESSON 1: EVOLUTION
ANSWERS
Generally speaking, all organisms change over time… from an embryotic state to a full adult state.
More specifically, you might change quite significantly by added more muscle mass from working out
or a tree might change seasonally by losing its leaves. However, neither of these processes
represents evolution in the biological sense.
2 Prokaryotic cells lack any membrane bound organelles whereas eukaryotic cells contain membrane
bound organelles such as the nucleus.
1
3
4
Life is thought to have begun 3-3.5 billion years ago. The first cell was likely to have been
prokaryotic.
5 Linnaeus is famous for developing the binomial system of classification.
6 He did not publish his ideas due to social and political factors such as the prevalence of religion at
the time. The theory of evolution conflicted with existing religious beliefs and gave importance to
scientific thought which threatened the power of religious institutions which had long held political and
social power.
7 According to Lamarck’s theory, your offspring would directly inherit the muscular, built physique that
you have acquired.
8 The theory of evolution caused political and social reactions. Religious beliefs stated that each
species was created in present form by God and remained unchanged and that humans had a special
place in the world. The idea of evolution went against this, stating that organisms have changed over
millions of years and implying that humans were descendants of apes which reduced humans to the
same level as every other organism. As such, the development and acceptance of the theory of
evolution was difficult due to social and political conflicts.
9
Date
Theorist/Scientist
Theory/Observation
Andreas Vesalius
Noticed similarities between various organisms.
Special note of physical features that humans have
with other organisms.
Nicolas Steno
Realised importance of fossils could tell us
something significant about past life on earth.
16th Century
17th Century
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YEAR 12 BIOLOGY
18th Century
Karl von Linné
18th Century
Erasmus Darwin
LESSON 1: EVOLUTION
Distinguished hybrids and cross pollination from
evolution.
Proposed that evolution occurred. But did not come
up with any mechanism for its occurrence.
Jean Baptiste Lamarck
Proposed theory of evolution by acquired
characteristics whereby adaptations developed
based on inner need.
Charles Darwin
Proposed theory of evolution by natural selection
which is the accepted mechanism today.
Alfred Wallace
Observed the same mechanism of natural selection
as Darwin.
19th Century
19th Century
19th Century
An organisms’ ability to reproduce is the best measurement of its ‘fitness’ from an evolutionary
perspective. If an organism can successfully reproduce, that means it has survived whatever harsh
environmental conditions might be present, it has found sufficient food and water, has mated, etc.
11 A new species would not be able to interbreed and produce fertile offspring with the original
population.
12 Variation in blubber thickness exists naturally within the whale population. The increase in water
temperature caused by global warming represents an environmental selection pressure. As such,
whales with thinner blubber (favourable in warm waters) will be naturally selected to survive at a
higher frequency than those with thick blubber. These whales with thinner blubber will survive to pass
on their traits to their offspring. Over time, the trait of thin blubber will become more prevalent in the
population. Thus, the whale population has evolved to have, on average, thinner blubbers than
previously.
13 All populations or groups of organisms have variation within the group (e.g. some giraffes have
longer necks than other giraffes). These changes can be caused by mutations in the genes of the
organism.
14Physically e.g. a river cuts through a valley and isolates two halves of the population, chemically e.g.
a new insecticide or antibiotic, and increased competition for resources e.g. drought, flood, new
predators.
15 Some organisms survive while others die out.
16 Reproduce.
17 They pass on their genes i.e. their characteristics. These may help their offspring to survive in the
changing environment (it may also cause them to die, depending on the change in the environment!).
18 Population will change to have the characteristics that allow survival to become more common e.g.
if a longer neck allows organisms to reach food better, then the population will slowly change to
include more long-necked organisms.
19 Speciation.
20 Variation within the species e.g. different beak shapes on predators.
21 The prey.
22 The organisms with the least food do not survive.
23 Generations or periods of time.
24 The predator with the beak shape that is most suited to catching prey will survive and the
population, over many generations, will slowly attain this beak shape.
25 The predators do not reproduce and pass on their characteristics to their offspring.
10
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YEAR 12 BIOLOGY
LESSON 1: EVOLUTION
26
Models are advantageous because they are simple demonstrations which assist in the
understanding of biological concepts. They also allow for demonstration of concepts which would
otherwise be difficult to observe e.g. evolution as this occurs over extended periods of time (millions
of years).
However, there are limitations in regards to the use of models. Firstly, models can tend to over-simply
complex biological concepts which may lead to misunderstandings. Furthermore, they may be unable
to account for some important details e.g. models of evolution are unable to demonstrate reproduction
and passing on of traits to successive offspring.
Despite these limitations, models of biological concepts generally provide a useful means improving
understanding.
27 The most widely held definition of species is that proposed by the famous biologist Ernst Mayr in
the 1940s - a species is an actually or potentially interbreeding population that does not interbreed
with other such populations when there is opportunity to do so.
28
Evolutionary biology is all about trying to determine how so many ‘species’ came about, and to do
that, you must have a good working definition of ‘species’ to start with.
29 There appears to be physical separation in allopatric speciation unlike sympatric speciation.
30 Isolation of part of a species can occur in a number of ways. Organisms can be cut off from the
main group by geological changes such as the drifting of continents, the formation of mountain
chains, the formation of canyons and rivers, or the formation of new islands and environments. It can
also be caused by climate changes e.g. the formation of deserts or rainforests, or by sudden natural
events such as floods, volcanoes or earthquakes.
31 Other behavioral changes, such as a modified bird song, could help drive the formation of a new
species within the same range. Genetic alterations and mutations can also give rise to new species
within the same range.
32 As each species of finch essentially inhabits a distinct island, the process would probably be best
described as allopatric. However, the birds are not necessarily ‘physically separated’ as they could
potentially fly from island to island. This does not usually take place though, and as their ranges do
not overlap, they are considered geographically distinct.
33 There was natural variation within the ancestral finch population; some had larger beaks, some had
smaller beaks. On the islands where many nuts were available, birds with larger beaks that could
crack and eat the nuts were able to survive, while others with smaller beaks were less likely to
survive. The large-beaked birds reproduced, and bred more large-beaked birds. Over time, the
population on these islands developed to mostly have large beaks.
On another island, there may have been many insects that hid in crevices, and not many nuts. Here,
birds that had small, sharp beaks were able to catch the insects, while others could not. Thus they
survived, reproduced, and passed on the small, sharp beak characteristic to their offspring. Over time,
the population changed to mostly contain sharp beaked birds.
Over many generations, the different finches’ genes became different enough that if they were placed
in the same mainland environment again, they could no longer breed and produce fertile offspring.
34 Protection from predators (spiny skin of hedgehog and echidna); running and hunting prey using
similar methods (Tasmania tiger and dogs).
35 This is due to the predator-prey relationship whereby Mako needs to be able to swim at least as
fast as the tuna, thus the similarity in tail muscles.
36
Type of
Evolution
Divergent
Convergent
Description
Examples
Process where two or more related species
become less similar, which may result in two or
more species.
Process where unrelated organisms evolve to
become more similar e.g. physical similarities
such as body form, colour as well as behavior.
Galapagos Finches, Californian
salamanders (allopatric), Cichlids
(sympatric).
Shark and dolphin, wings in bats and
birds.
37
Sydney has a milder climate than far north NSW which is expected to be hotter and drier. As such,
under Darwin/Wallace’s theory of evolution by natural selection, divergent evolution may occur.
Firstly, these plants have natural variation e.g. in colour, size, roots. Therefore, in Sydney, plants
more suited to a mild climate will survive and reproduce to increase the frequency of these types of
plants. In far north NSW, those plants with traits that are suitable to a drier hotter, climate e.g. deep
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YEAR 12 BIOLOGY
LESSON 1: EVOLUTION
roots to reach water sources underground, will survive and reproduce, eventually increasing the
prevalence of these traits. Over time, the characteristic differences between the plants in each area
can become so pronounced that they may no longer interbreed and as such they would have
diverged into two separate species suited to each environment.
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