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BiologyHSC CourseStage 6

Blueprint of life

Part 1: Evolution

Incorporating October 2002

AMENDMENTS

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Part 1: Evolution

Contents

Introduction ................................................................................2

Environment and evolution.........................................................5

Earth’s constantly changing environment ...........................................6

Modelling natural selection ..................................................................9

A case study .......................................................................................13

Evidence for evolution..............................................................14

Fossils ................................................................................................15

Transitional forms...............................................................................23

Biogeography .....................................................................................25

Comparative anatomy........................................................................29

Comparative embryology ...................................................................30

Biochemistry .......................................................................................32

Other evidence ...................................................................................33

The evolution of evolution ........................................................38

Additional resources ................................................................41

Suggested answers .................................................................51

Exercises – Part 1....................................................................57

2 Blueprint of life

Introduction

Popular culture often depicts the process of evolution as a development of organisms from

lower simple forms to higher and more sophisticated states of organisation. These

descriptions often place humans at the top of the evolutionary ladder. This is a notion as

outdated as the Earth being the centre of the universe.

The famous American evolutionary biologist, Stephen Jay Gould said:

Darwin’s revolution will be completed when we smash the pedestal

of arrogance and own the plain implications of evolution for life’s non-predictable

nondirectionality.

That is, evolution does not necessarily produce more complex and sophisticated organisms.

Rather, it produces different ones.

The evolution of species results from changes in the environment. Individual members of a

species that can survive the pressures of change have some special features, called

adaptations, which enable it to cope and to reproduce.

The first part of this unit deals with the nature of these environmental changes – be they

physical, chemical or a result of competition for scarce resources.

You will be asked to prepare a case study either on the evolution of the Australian megapods

(kangaroos) or the plant Nothofagus, showing how changes in the Australian environment

have led to changes in a species.

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Part 1: Evolution

Many sciences today describe and explain how present and past species are related to each

other. Evidence that species evolve from a common ancestor has come from studies such as

palaeontology (the study of fossils), comparative anatomy and embryology.

The sciences of biogeography (the study of the distribution of organisms) and biochemistry

(the study of molecules that make up living matter) also reinforce what is understood about

evolution. This part of the module will describe, using specific examples, how evolution is

supported by these studies.

To complete an activity in this unit you will need red and green food colouring, a packet of

toothpicks, two small plates, two forks and some paper towel. Please get them ready before

you start this part.

In this part you will have the opportunity to learn to:

• outline the impact on the evolution of plants and animals of:

– changes in physical conditions in the environment

– changes in chemical conditions in the environment

– competition for resources

• describe, using specific examples, how the theory of evolution is supported by the

following areas of study:

– palaeontology, including fossils that have been considered

transitional forms

– biogeography

– comparative embryology

– comparative anatomy

– biochemistry

• explain how Darwin/Wallace’s theory of evolution by natural selection and isolation

accounts for divergent evolution and convergent evolution.

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In this part you will have the opportunity to:

• plan, choose equipment or resources and perform a first-hand investigation to model

natural selection

• analyse information from secondary sources to prepare a case study to show how an

environmental change can lead to changes in a species

• perform a first-hand investigation or gather information from secondary sources (including

photographs/ diagrams/models) to observe, analyse and compare the structure of a range of

vertebrate forelimbs

• 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.

Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued 1999. The most

up-to-date version can be found on the Board's website at

http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html This version October

2002.

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Part 1: Evolution

Environment andevolution

The fact that species become extinct indicates that its members were not very successful at

coping with changes in their environment. Whether they were sudden or gradual changes, the

fact remains that the members of the species did not survive the pressures of change and were

not able to thrive and reproduce.

Adaptations to suit environments

Your experiences with nature and living things on Earth have probably come from reading

books, watching television and video, and going out in the bush or to the beach. You may

have had the opportunity to go to different environments around Australia or even to other

parts of the world. The Preliminary course must have also broadened your ideas about life on

Earth.

Whatever your experiences and observations have been, you would conclude that living

things survive best in the environment that they are most suited for. What is less obvious is

that all living things evolved to become suited to the environment that they live in. While

adaptations are easily observed and described, the evolution of these adaptive features is not

usually noticed in a human lifetime.

In past times, people thought that species never changed and neither did the environment.

Today we know that the environment is constantly changing and that species evolve to make

the most of conditions in their background. Species with features most suited to their

environment thrive and live to reproduce.

Environments on Earth are diverse; therefore there is a diverse range of life on the planet.

Some environments change periodically, for example, seasons. Some environments have

regular changes over longer periods of time. Sometimes environments change gradually over

millions of years; at other times, environments may undergo a sudden drastic change.

Whichever way the environment changes, the organisms living there have pressure put on

them to survive. The adaptive features of individuals give them survival value.

Environmental pressure selects those individuals with the greatest survival value.

Using the information you have just read, write a paragraph to state the link

between the environment and evolution of organisms.

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_________________________________________________________

_________________________________________________________

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Check your answer.

Earth’s constantly changing environment

Changes to the environment can be grouped into one of the following:

• changes in physical conditions

These include any non-living natural conditions such as wind, temperature and

availability of water. Some changes in physical conditions can occur suddenly or

annually.

• changes in chemical conditions

The concentration of chemicals in the environment that an organism uses or is adapted to

may change. For example, the salt concentration (salinity) in soil or in water might

increase.

• competition for resources

Changes to the amount of resources available affects the struggle for survival among the

species and within the species. Situations such as the introduction of a successful

competitor change the dynamics in a community, often causing a strain on resources.

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Part 1: Evolution

Think about all the possible changes that can happen in an environment.

For example, the climate may become warmer or a new species may be

introduced into an area.

1 List as many features in the environment that you can think of that change over a period

of time.

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2 Now group these changes into physical, chemical and ones caused by changes to

competition. List these in the table below.

Physical Chemical Changes to competition

3 A number of scenarios to do with environmental change are listed below. Describe an

adaptive feature of an animal and/or a plant that will help it to survive the change.

a) An area dries out because of climatic changes.

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b) A new species of frog moves in, reproducing and spreading rapidly. It is poisonous

to the predators of the new area.

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c) The salinity (amount of salt) of the soil of an area slowly increases.

__________________________________________________

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Check all your answers.

Most biologists today agree that major evolutionary changes have been associated with

dramatic changes to the Earth’s environment. These changes have mostly been brought about

by the drifting continents, causing ocean currents to change as well as affecting volcanic

activity and mountain building.

More recently, scientists have shown direct links between mass extinctions (where most

species on Earth become extinct over a short period of time) and collisions with

extraterrestrial objects such as comets and meteoroids.

Do Exercise 1.1 now.

Modelling natural selection

In the module called Evolution of Australian biota, you learnt that changes in a population are

due to selection pressures. Perhaps the best example of this is the classic study of the

peppered moth.

An example of natural selection

This is a historically interesting example of natural selection. The original experiment has

been criticised because there is some doubt as to whether the moths are found on tree trunks.

The moths are usually found under leaves and branches. Further discredit has come because

the original published photographs of the moths were achieved by gluing the moths to the

trunk of a tree. However it still serves as an example of how natural selection may occur.

There are two forms (light and dark) of the moth occurring naturally in the population. In

industrial areas the trees were blackened by soot from the factory chimneys. When the dark

moths rested on tree trunks during the day, they were less obvious to the birds that fed on

them, while the light variation was easily seen and more often taken by these predators. In

these areas, light coloured moths became less and less common.

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Part 1: Evolution

In the non-industrial areas the opposite was the case – the light coloured variation was harder

to see against the light backgrounds of the trees so fewer were taken by predators. These

were then able to reproduce and form the next generation. It was the dark coloured moths that

disappeared.

The light variation is easily seen on the dark background and the dark variation is easily seen on thelight background.

Biologists attempt to explain the evolution of camouflage by using the principles of natural

selection. If individuals of a population are obvious to their natural predators, then their

numbers would be fewer than those that blend into their environment.

An open-ended investigation of natural selection

In this experiment you are going to model natural selection by observing

which colours are most easily selected against different backgrounds.

Plan and perform your own activity if you can, or follow the instructions

provided on the following pages.

Aim

To demonstrate the process of natural selection

Equipment

You will need:

• small bottles of red and green food colouring from the supermarket

• a packet of about 100–200 toothpicks

• two small plates and two forks

• paper towel.

Method–preparation

1 Place 50 toothpicks in each plate. Colour one plate red and the other green by pouring

enough food colouring over the toothpicks so that they are immersed in the colouring

liquid.

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FOOD

COLOURING

fork

plate

toothpicks

2 Leave the toothpicks in the liquid for at least half an hour. Make sure the toothpicks are

stained all over by stirring them around with the fork.

3 Using the fork, scrape the toothpicks out of the plate and onto some paper towels to dry.

4 Once they are dry you should have a bunch of 100 toothpicks – 50 red, 50 green.

5 Shuffle these around in your hand so that they are randomly mixed.

6 Now you are going to model natural selection by observing which colours are selected

against different backgrounds.

7 You should choose either a member of your family or a friend to act as the predator. You

will do if you are unable to get anyone else. The toothpicks act as the prey and the

background colour will be the environment.

Steps

1 Sprinkle the random bunch of toothpicks over an area of green surface, such as a lawn or

a green blanket.

2 Get the predator to stand about 5 metres away. When you signal, the predator must run up

to the area and randomly pick 10 toothpicks in less than 10 seconds. The predator then

runs back, puts down what has been collected, and runs back to do it again. In total, the

predator picks up five bunches of 10 toothpicks (50 toothpicks all together).

3 Sort the toothpicks using their colour, count them and record the information in the table

below.

4 Do at least 5 trials.

5 Repeat the entire experiment on a neutral coloured background such as a concrete surface

or wooden floor. Record these results in the table below.

Results

Record your results in the table on the following page.

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Part 1: Evolution

On green background On neutral background

Trial Red Green Red Green

1

2

3

4

5

Average

Write a statement comparing the results for the green background and the neutral background.

_________________________________________________________

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Conclusion

You must account for the difference between the results obtained with the green background

compared with the neutral background. Answer the following questions.

1 Predict the results you would obtain if the experiment were repeated on a reddish pink

background.

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2 Assume that the predator is always present in this environment. If the toothpicks were

able to breed, what could be the most frequent colour found in a few generations when:

a) the background is reddish-pink

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b) the background is green.

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3 Write an explanation for selection by camouflage.

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_____________________________________________________

_____________________________________________________

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Do Exercise 1.2 now.

A case study

Your task in this case study is to show how changes in physical or

chemical conditions or increased competition for resources have led to

changes in an Australian species.

Use resources such as the Internet and books, as well as the information

given in the Additional resources section of this part.

Here are two possible case studies that you may choose for this activity.

Case study 1: The evolution of kangaroos

Australia has undergone changes in its climate over time. The kangaroo is a good example of

a species that has evolved over a long period of time in response to these climatic changes.

Case study 2: The distribution of the Southern Antarctic beech

This tree had a wide distribution in previous times. Now it is restricted to small pockets in

rainforests.

Prepare a short case study and present your report in Exercise 1.3.

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Part 1: Evolution

Evidence for evolution

For any real links between changes in the environment and the evolution of life, scientists

have to make observations that span many millions of years. This can only be done by

indirect methods.

Since Charles Darwin’s book, On the origin of species, was first published in 18 9,

overwhelming support for evolution has came from all areas of science.

The science of palaeontology (the study of fossils) has provided evidence for the evolution

and history of life on Earth. Palaeontologists have been documenting details of past life

forms (the fossil records) and working out when they existed and how they may have

evolved.

The science of anatomy shows similarities between closely related species by describing

features of their body structure that they have in common. Comparisons between the embryos

of related species is further support for the idea that species have common ancestors.

Advances in technology, especially in biochemical and DNA analysis, have given

biochemists the best tools yet to accurately describe the relationships between species. This

further supports the theory of evolution.

In summary, evidence for evolution comes from:

• palaeontology

• biogeography

• comparative anatomy

• comparative embryology

• biochemistry.

You will investigate some of this evidence in more detail on the following pages.

Fossils

A palaeontologist is a scientist who studies fossils. Since the movie, Jurassic Park,

palaeontology has become very glamorous but in reality only a few scientists get to study

exciting dinosaur fossils.

4 Blueprint of life

Reconstructed Tyrannosaurus Rex skeleton at the American Museum of Natural History, New York(Photo: R Caddy)

Most palaeontologists are busy trying to fill in missing details of the life histories of less

spectacular organisms.

Fossilised worm burrows (Photo: T Reid)

The fossil records have revealed a few interesting facts about the history and evolution of life

on Earth.

• All the species of living organisms on the Earth today represent only a minute number of

the species that have ever lived here over the past three and a half billion years.

• The species that exist on Earth today have similarities to some of the pre-existing life

forms found in the fossil records.

• New fossils are constantly being discovered and their clues are giving scientists a clearer

picture of the relationships between past and present life.

The work of a palaeontologist involves more than hunting for fossils, digging them out and

preparing them for exhibition in museums. Palaeontologists are also concerned with trying to

work out what changes took place in organisms over geological time, and what relationships

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Part 1: Evolution

the various fossils bear to one another. This requires careful study of large numbers of fossils

(often mere fragments) and detailed comparisons between the fossil material available.

Fossilised leaf of an extinct plant called Glossopteris (Photo: M Khun)

Palaeontologists, like most other scientists, usually record both their data and their

comparisons as measurements. Much of this work is done in the laboratory.

To better understand the information available from fossils, you are going to study some of

the fossil record of a group of organisms – horses.

The fossil record of horses

Some groups of organisms are very well represented in the fossil record. One of these groups

is the horse family, for which large numbers of fossils have been found in North America,

Europe and Asia. Their skeletal remains, particularly those of the teeth and toes, have given

important clues to the relationships between them. It has been possible to suggest the early

history of the horse family from this evidence.

Background Information

Horses have their grinding teeth at the back of the mouth, separated from the front teeth by a

toothless space. Their grinding teeth (cheek teeth) consist of three premolars and three molars

on either side of the jaw. The skeletal characteristic to be used in this exercise is the distance

spanned by the cheek teeth.

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span of cheek teeth

premolars molars

Horse skull showing how the span of cheek teeth is measured.

Optional

This activity is designed to give you an idea about the way that

palaeontologists work out the changes that took place in organisms

over millions of years. (It is adapted from material by H Messel in

Science for High School Students.)

Aim

To infer likely relationships between various horses of the past, using some of the methods of

the palaeontologist

Procedure

The span of the cheek teeth has been measured in many fossil specimens of horses. The data

for seventeen of the twenty or so known genera are presented in the table on the following

page.

Genera of equidae Time of existence Span of cheek teeth (cm)

1 Hyracotherium Early Eocene 4.3

2 Orohippus Middle Eocene 4.3

3 Epihippus Late Eocene 4.7

Early Oligocene 7.24 Mesohippus

Middle Oligocene 7.3

Late Oligocene 8.45 Miohippus

Early Miocene 8.3

6 Parahippus Early Miocene 10.0

7 Anchitherium Early Miocene 11.3

8 Archaeoshippus Middle Miocene 6.5

Middle Miocene 10 29 Merychippus

Late Miocene 12.5

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Part 1: Evolution

10 Hypohippus Late Miocene 14.2

11 Megahippus Early Pliocene 21.5

Early Pliocene 15.512 Pliohippus

Middle Pliocene 15.6

Early Pliocene 11.013 Nannippus

Late Pliocene 10.7

14 Calippus Early Pliocene 9.3

15 Neohipparion Middle Pliocene 13.1

Middle Pliocene 11.816 Astrohippus

Late Pliocene 11.8

Late Pliocene 18.817 Equus

Pleistocene 17.6

Each measurement has been plotted as short bars on the graph grid below.

Beside each bar plotted, write the number from the table of the genus it

represents. The first one is done for you.

1

Early Middle Late Early Middle Late Early Middle Late Early Middle Late

EOCENE OLIGOCENE MIOCENE PLIOCENE

PLE

IST

OC

EN

E

24

20

16

12

8

4

0

M i l l i o n s o f y e a r s a g o

Sp

an

of

ch

ee

k t

ee

th (

in c

m)

60 40 30 10 1 0

Check your answer before proceeding.

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How have the spans of cheek teeth changed between genera living at different times? Find

out by following the instructions and answering the questions that follow.

Start at the oldest genus (Hyracotherium) and work towards the younger fossils. Draw pencil

lines between the bar representing each genus and the bar representing another younger

genus.

Connect the points representing the genera Hyracotherium, Orohippus, Epihippus,

Mesohippus, and Miohippus.

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Part 1: Evolution

1 Why can’t you join two or three genera that occurred at the same time?

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2 Determine what appears to have happened to the span of the cheek teeth in horses up to

late Oligocene times.

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3 Continue the graph by showing the relationship between late Oligocene and early

Miocene genera. The change in span of cheek teeth can be shown by a single line up to

the late Oligocene. What happens from that time to the early Miocene?

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4 What does this suggest about the origin of Parahippus and Anchitherium?

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5 Working with your pencil, complete the graph to the Pleistocene by indicating what you

consider to be the relationships between the various genera. What problem are you

confronted with?

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6 When you have completed your graph, compare it with the graphs drawn in the suggested

answers. What could you do to help decide which graph was best?

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Since the fossil material is abundant, particularly in western North America, palaeontologists

are able to consider a great many structural characteristics when working out relationships

between these horse-like animals. The relationships based on any single characteristic like the

span of cheek teeth may conflict with relationships worked out from other characteristics. The

20 Blueprint of life

most widely accepted hypothesis of relationships, based on all available data to date, is shown

in the figure following.

Calippus

NannippusMegahippus

Hypohippus

Anchitherium

Equus

Pliohippus

Merychippus

Parahippus

Miohippus

Mesohippus

Epihippus

Orohippus

Hyracatherium

Neohipparion

Astrohippus

Archaeohippus

Are all the relationships proposed by your graph the same as the relationships proposed in the

figure you have just studied? Consider any similarities or differences then answer the

questions below.

Conclusion

7 What was the approximate average change in cheek teeth span per million years from

Hyracotherium to Miohippus?

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8 What was the approximate average change in cheek teeth span per million years from

Miohippus to Equus?

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Part 1: Evolution

9 From these results, what generalisation can be made about the rate of evolution of

horses? (This may serve as an indication of the rates of evolution one might find in other

organisms.)

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10 There are countless millions of fossils in sedimentary rocks throughout the world. Yet

the history of life on Earth is still very incompletely known. List as many reasons as you

can why this is so.

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_____________________________________________________

_____________________________________________________

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Check all your answers.

Transitional forms

The example you have just examined of the evolution of the horse is well studied because

there is an abundance of fossil material.

Palaeontologists have been able to describe the relationships between these fossils because the

links between one form and another have been found. The ancestral tree of 60 million years

of horse evolution shows a gradual development from one genera to the next while giving rise

to other groups.

However most fossil records tracing the ancestors of groups of organisms are not as complete

as the horse. With no fossils showing features intermediate between two forms that are

believed to be linked, scientists have a hard time explaining natural selection.

You may have seen newspaper headlines like:

Scientists find fossil believed to be the missing link!

These refer to the discovery of human fossils believed to show our knowledge of human

evolution. Intermediate forms or links are called transitional forms.


Transitional fossils

A transitional fossil is the fossil of a transitional form. A transitional form, as traditionally

used, meant an organism halfway between two classes or kinds of organisms. Archaeopteryx

is often used as an example of an intermediate form between a reptile and bird.

Archaeopteryx was once believed to be an intermediate form between reptile and bird.

However, this view of evolution is outdated. Archaeopteryx is not a transitional form

between reptile and bird. It is both reptile and bird or a class of its own. (Remember that a

classification system is something invented by humans and imposed on nature.)

One of the problems Darwin had explaining natural selection was the big difference in

features between the classes. Transitional fossils were supposed to bridge the gap or be the

missing link in the fossil record.

Modern biologists explain these differences by saying there is a gap in the fossil record. As

more fossils are found, these gaps will be filled and the gradual progression of change will be

shown.

Why do palaeontologists continue to look for transitional forms in the

fossil record?

_________________________________________________________

_________________________________________________________

_________________________________________________________

Check your answer.

Equilibrium

In 1972, after studying many fossil observations, Eldredge and Gould claimed that most

species appear suddenly and their history shows little evidence of change. Individual

populations might change both genetically and structurally due to adaptation but overall a

species exhibits a net equilibrium. That is, it tends to stay much the same.

To explain why transitional fossils are not found, Niles Eldredge and Stephen Jay Gould

(1972) came up with the punctuated equilibrium model of evolution.

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Part 1: Evolution

Punctuated equilibrium

This view suggests that species originate suddenly whenever rapid changes in the

environment occur. This abrupt appearance of new species is a random event and is usually

associated with a large number of extinctions called mass extinction.

You will learn more about this concept when you do part 4 of this module.

Biogeography

Biogeography (sometimes called zoogeography) is the study of the distribution of organisms.

It is a science that describes where plant and animal families are found on the Earth today and

tries to explain how they came to be where they are. Biogeography explains these

distributions by bringing together concepts from biology, geology, palaeontology and

chemistry.

The science of biogeography had its beginnings in the early part of the last century and

depends heavily on the work of Charles Darwin and Alfred Russel Wallace, among others.

Notice that these same individuals were prominent in developing the theory of evolution by

natural selection.

Biogeography as evidence for evolution

Each region has similar species occupying similar niches within its borders. However, the

species are clearly different from those in adjacent areas.

The boundaries between biogeographic zones are drawn according to the distribution of

vertebrate groups (in particular, families). The regions are based on the relationships of birds;

but the same regional limits work well enough for fish, amphibians, reptiles and mammals.

There are six biogeographical zones (or provinces), each with distinct flora and fauna. Theyare:

• Palaearctic – North Africa, North Europe and Northern Asia

• Ethiopian – Africa below the Sahara desert

• Australian – Australia

• Nearctic – North America

• Neotropical – South America

• Oriental – Southeast Asia and India.

These zones are shown on the map of the world following.


2

3

3

3

N

Australian

Ethiopian

Oriental

Neotropical

PalaearcticNearctic

Biogeographic zones of the world.

Look at the map of biogeographic zones above.

With what physical features of the Earth do the borders coincide?

_________________________________________________________

_________________________________________________________

Check your answer.

Populations that become geographically isolated by means of a barrier will tend to change.

These barriers include seaways, rivers, mountain ranges, deserts and other hostile

environments. They put a wedge between whole groups of organisms, eventually causing

related organisms – species, genera, families and so on – to diverge.

Wallace’s line

Alfred Russel Wallace, the so-called father of animal geography, formulated his ideas on

evolution by natural selection while observing and collecting wildlife in the islands of

Southeast Asia. He was particularly impressed by the sudden difference in bird families he

encountered when he sailed some twenty miles east of the island of Bali and landed on

Lombok.

On Bali the birds were clearly related to those of the larger islands of Java and Sumatra and

mainland Malaysia. On Lombok the birds were clearly related to those of New Guinea and

Australia. He marked the channel between Bali and Lombok as the divide between the

Oriental and Australian biogeographic zones.

In his honour this dividing line, which extends northward between Borneo and Sulawesi, is

still referred to today as Wallace’s Line.

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Part 1: Evolution

P a c i f i c O c e a n

I n d i a n O c e a n

S o u t h C h i n a S e a

B a n d a S e a

0 100 200 300 400 500 Kms

Irian Jaya

Timor

Gulf ofCarpentaria

Australia

Singapore

Sumatra

J a v a S e a

Flores

Thailand

M a l a y s i a Brune i

A r a f u r a S e a

T i m o r S e a

C e l e b e sS e a

Sabah

PapuaNew Guinea

B a l i

Wallace’s Line

Phi l ipp ines

Borneo

Kal imantan

J a v a

Halmahera

Lombok

Sulawes i

Map of South-East Asia showing Wallace’s line.

To the west, the Asian animal community includes such mammals as the rhinoceros,

orangutan, tapir, tiger and elephant. To the east are found animals related to Australian fauna.

They include birds such as cockatoos, bowerbirds and birds of paradise as well as marsupials

such as bandicoots and cuscus.

The core areas of the Oriental and Australian provinces are clearly distinct but overlaps exist

on the edges of the boarders. Thus some biogeographers recognise the region of islands

between Java and New Guinea as a mixing zone of Oriental and Australian fauna.

Rather than try to fix where the line between these two realms should lie, most modern

biologists recognise that the whole Indonesian archipelago region represents a zone of

changeover. Within this zone, the two faunas progressively replace one another.

This changeover zone exists because, as the Asian and Australian landmasses drifted closer

together, organisms were able to move out of the places where they originated into new

territories.

When the world is divided into zones using the distribution of flowering

plant groups, the resulting zones do not coincide with biogeographic zones

based on vertebrates. What factors could account for the differences in the

distribution patterns of vertebrates and flowering plants?

_________________________________________________________

_________________________________________________________

Check your answer.

Biogeographic distributions

There are three important principles used to determine a biogeographic zone.

• Environment cannot account for either similarity or dissimilarity, since similar

environments can harbour entirely different species groups.

• Affinity or similarity of groups on the same continent (or sea) is closer than between

continents (or seas).

• Geographical barriers, such as seas, oceans and mountain chains, usually divide these

different groups. The degree of difference between families relates to the rate of

migration or ability to disperse across the barriers.


Look back at the world map that shows the biogeographic zones of the world. Think about

the different kinds of plants and animals in each zone. Think about the different

environmental conditions in each zone. Try to think of some examples to illustrate each of

the principles above.

For example, environmental conditions in parts of the Ethiopian zone are similar to conditions

in the Australian zone. Some organisms in these zones, such as arid area plants, are very

similar. However, some organisms, such as gazelle and kangaroos, are very different. Within

the Australian zone, species of kangaroo and wallaby are much more similar to each other

than they are to organisms in other zones. And notice the positions of the lines separating

zones – oceans separate the Australian zone from other zones, whereas the Oriental and

Palaearctic zones are separated from each other by the Himalayas.

Six degrees of separation

Remember that the degree of separation is the amount of difference between similar groups of

organisms. Three criteria of mammalian families and their distribution patterns are used to

delineate the six regions known as biogeographic zones, or provinces. These are:

• the total number of families

• the number of families originating from (endemic to) this province. This is a measure of

uniqueness of the mammalian fauna

• the number and location of other regions with which mammalian families are shared.

Rank the biogeographic zones by dividing the number of endemic families

by the number of shared families. (Hint: Australia would be first because

it only has eight endemic families and only one shared family.

The calculations have been done in the first row as an example.)

eographic Total number offamilies

Number ofendemic families

Number ofshared families

Endemic familiesshared families

pian 38 12 2 12

2= 6

opical 32 16 3

al 30 4 3

arctic 28 2 3

tic 24 4 3

alian 9 8 1

Check your answers.

The comparison of endemic to shared families is used as a measure of how much biological

separation exists between mammals of the biogeographic zones.

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Part 1: Evolution

Now complete Exercise 1.4.

Comparative anatomy

Different groups of organisms often have similar structural features. This observation is also

used as evidence that species can evolve from a common ancestor.

Comparing the mouthparts of insects

The mouthparts of insects are an example of a similar structure modified for its function. In

various insects, the same basic plan has been functionally modified for biting, piercing,

chewing or sucking.

Vestigial structures

Those structures that functioned in ancestral organisms but are reduced (in structure andfunction) in the descendant are called vestigial structures. Some examples in humans includevertebrae of coccyx (tailbone) and the appendix on the intestines. In some other mammals,

the appendix is a larger organ with a function in digestion.

Comparing vertebrate forelimbs

The skeletons of vertebrates provide a clear example of structural similarities. The five

fingered limbs (called pentadactyl limbs) of vertebrates are considered to be similar

structures. The hand of a human, the forefoot of a horse, the flipper of a dolphin and the wing

of a bat all have the five-fingered plan. The same basic plan is modified to serve a different

function for each type of vertebrate.

In your next exercise you will need to observe, analyse and compare the structure of a range

of vertebrate forelimbs. You can do this by looking at some in a museum, looking them up

on the Internet and/or using information in the diagram in Exercise 1.5.

You will find some helpful starting points on the Science online webpage at:

http://www.lmpc.edu.au/science

Now complete the tasks in Exercise 1.5.

Comparative embryology

Embryology is the study of embryos and their development. Embryologists have discovered

that all vertebrate embryos look alike during their early development. It is almost impossible

to distinguish between the early embryos of fish, chickens and humans. They become

recognisable later in their development.


The common features of embryo development

found throughout the vertebrate group include:

• gill slits appear even in embryos of fully

terrestrial organisms with no sign of gills

as adults.

• tail

• notochord develops into vertebrae in

all vertebrates.

gill slits

notochord

tail

A vertebrate embryo.(Adapted from Messel, Science forHigh School Students)

Study the following diagram showing the stages of development of four

vertebrate groups and determine which row shows the most similarity.

man pig salamander fowl

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Part 1: Evolution

Stages of development of four vertebrate groups.

(Adapted from Messel, Science for High School Students)

Check your answer.

Biochemistry

The building blocks of life are fundamentally the same for all living things and they use thesame basic biological molecules for similar functions. For example, the amino acid building

block molecules are the same in all known species. Biochemists can analyse the sequence of

amino acids of a protein common to many species, match the similarities and then compare

them with other species.

The table below shows the number of amino acids for a common protein called cytochrome c

that are different in humans and another species.

Species compared Number of different amino acids

human/chimpanzee 0

human/horse 7

human/snake 11

human/fly 13

human/cauliflower 19

human/yeast 26

1 Based on the similarities between amino acid sequences for

cytochrome c:

a) which species is the most similar to humans? _____________

b) which is the least similar to humans? ____________________

2 What can you infer from this information?

_____________________________________________________

_____________________________________________________

_____________________________________________________

Check your answers.

There are many more techniques used by biochemists and molecular biologists for showing

similarities between species. A good example is DNA sequencing. These techniques are

better explained further on in the module after you have learnt about DNA and biotechnology

in Part 4.


Other evidence

There are two other ways to organise evidence that are used to support the theory of

evolution. These use observations from the areas you have already considered (comparative

anatomy and so on).

These other ways are:

• divergent evolution

• convergent evolution.

Divergent evolutionWhen a new area, such as an island, appears or something causes an area to become vacant,

colonising organisms move in. Those with features best suited to the new environment will

function more efficiently, thrive and produce offspring because there will be little competition

for resources. Adaptations make it possible for these colonising organisms to cope with the

new (changed) environmental conditions.

Because organisms in a population are slightly different from each other, groups within the

population will be able to thrive and reproduce best in different parts of the new environment,

so the groups will gradually become different from each other. Or, different species could

become more alike to better use the same environment. This is divergent radiation.

Divergent radiation commonly occurs immediately following an evolutionary breakthrough.

This means a population with an innovative, better adapted feature colonises a vacant

ecosystem, speciates (forms species) and radiates to occupy the available space. (Speciation

can also occur in the same environment.)

An example of divergent radiation – dinosaurs and mammals

At the beginning of the Triassic period, some 250 million years ago, the terrestrial surface of

Earth had many environments unoccupied by vertebrates. The only vertebrates living on land

were amphibians and these were restricted to wet areas close to rivers, lakes and the coast.

1 Why didn’t the amphibians venture inland?

_____________________________________________________

_____________________________________________________

_____________________________________________________

2 Which group of animals would have lived inland?

_____________________________________________________

By the middle and toward the end of the Triassic period, a variety of

egg-laying vertebrates evolved and diversified to occupy every environment on Earth,

including the seas. They were, of course, the dinosaurs. They are well documented in books,

museums, videos and movies. Their dominance on the planet was to span the Jurassic period

and last some 200 million years.

3 What feature did dinosaurs possess that enabled them to venture away from water?

_____________________________________________________

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Part 1: Evolution

_____________________________________________________

Mammals evolved during the Triassic period but had to be content with occupying the nooks

and crannies of a planet dominated by dinosaurs. Fossils of mammals from around these

times show them to be small

rat-like creatures with little variation among them. They remained this way for 100 million

years.

A mass extinction event, believed to be due to a collision with an asteroid, caused the dinosaurs to

rapidly disappear from their dominant position. Only one variety is thought to have survived to

become the ancestor of birds.

Around 60 million years ago, with the dinosaurs out of the way, the mammals began to

occupy environments and niches left vacant by their previous occupants. The fossil record

shows a sudden increase in diversity of mammal forms. Eventually millions of mammals

ended up dominating almost every environment on Earth. Some varieties occupying the seas

and oceans gradually changed to become the whales and dolphins of today.

4 What factors lead to the sudden increase in mammal’s diversity?

_____________________________________________________

_____________________________________________________

_____________________________________________________

5 Explain what divergent radiation means in your own words.

_____________________________________________________

_____________________________________________________

_____________________________________________________

Check your answers.

Darwin’s finches

The finches of the Galapagos Islands are examples of many species evolving from one, to

take advantage of the available environments.

Diversity in a species may eventually result in speciation, which is the creation of new

species, when an area or environment has not reached its potential or been fully colonised.

The kind of adaptive radiation that leads to the evolution of many divergent forms from one

species is called divergent evolution.

It is believed that one species of finch may have arrived on a Galapagos island and then

divergent evolution lead to the many different species of finch found on the Galapagos Islands

today.


Different beak structures in finches found on different islands in the Galapagos.This illustrates how thespecies has diverged from the original form .

Charles Darwin explained divergent radiation by using the finches of the

Galapagos Islands as an example. Look up this work in a biology book at

your local library or on the Internet (use the words Galapagos, finches and

Darwin in a search engine). Then complete Exercise 1.6.

Convergent evolution

Today there is a staggering array of life forms on the Earth and each reflects diverse ways of

life. There are probably as many ways of life as there are species.

Many organisms that have evolved independently now live in very similar ways. Organisms

that live in similar environments have the same selective pressures applied to them. In the

example below there are three different vertebrates groups, all showing a similar body

structure. This is called convergent evolution.

mammal

reptile

fish

The diagrams above show major vertebrate groups that occupied the seas.

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Part 1: Evolution

1 What physical features do all these animals have in common?

_____________________________________________________

_____________________________________________________

_____________________________________________________

2 Although each sea creature represents a completely different vertebrate group, they all

look very similar. How would the theory of natural selection (by Darwin and Wallace)

explain what caused each of these vertebrate groups to have the same body shape?

_____________________________________________________

_____________________________________________________

_____________________________________________________

Check your answers.

Another example of convergent evolution can be seen in the shape of wings for flying. The

diagram below illustrates this example.

pterosaur

bat

bird

Adaptation to flight is an example of convergent evolution.


The evolution of evolution

A requirement for this part of the course is that you

assess the social and political influences on the historical development of theories of

evolution.

What does this mean? You can find out by reading the information below and answering the

questions. Then you will have a clearer understanding of how and why theories of evolution

develop.

Introducing the idea of evolution

It is one thing to discover and explain the workings of nature but the rest of society has to

understand and accept it. Developing an understanding of how species evolve has been one

of the greatest human intellectual endeavours throughout history.

This long journey of discovery took humans from considering themselves as the most

magnificent of God’s creations to just another species of animal and a very recent arrival at

that. The problem with the scientific explanation for evolution is that it challenged the

foundations upon which western culture is based.

Western societies were governed by religious institutions that controlled not only politics but

also the way people viewed nature. The idea that God made ‘man’ in his image to rule over

all other living things was indisputable. Therefore any challenge to this idea was seen as a

threat to the establishment.

What restrictions were there in society to alternative explanations for the

nature of life on Earth?

_________________________________________________________

_________________________________________________________

Check your answer.

A variation in viewpoint

The two statements below contrast the way ‘variations among individuals in a population’

was viewed during ancient Greek times in comparison with modern biology today.

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Part 1: Evolution

Ancient Greek – Plato’s view from ‘The Republic’

Each species is a fixed entity that never changes. All individual variations in a population are

unimportant imperfections of the ideal form. The perfect ‘essence of form’ is made up of the

best parts of the various individuals.

Nineteenth century – Darwin’s view from ‘On the origin of species’

Species have always been changing and always will. Variations among individuals of a

population are necessary for natural selection – the chief agent of change. It is these very

differences between individuals that make evolution possible and inevitable.

The current view

Since Darwin/Wallace’s explanations for evolution were first proposed, the science of modern

biology was born. Today, biologists use the principles of evolution by natural selection in

their everyday work.

In the Additional resources section, there is a summary of the major scientific thinkers who

have contributed to the modern theory of evolution. Read these now.

Then complete Exercise 1.7.

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Part 1: Evolution

Additional resources

Case study 1: The evolution of kangaroos

Based upon research in Kangaroos: 15 Million years of Australian bounders by Tim Flannery

“The kangaroos offer a unique opportunity to study evolutionary changes within a group of

Australian mammals”. This is because they have “the best known fossil record and are the

most extensively studied of all Australian mammals”. Also because they have undergone

rapid evolutionary change and are “commonly good indicators of restricted environments”.

Tim Flannery

The earliest record of kangaroos is found among the fossils of the Etadunna formation in

central Australia. These deposits were formed during the late Oligocene to early Miocene

epoch, some 25–15 million years ago.

This region, now a hot dry desert, was cool to temperate and the rainfall was consistently

moderate, with many freshwater lakes and rivers.

It was heavily forested and supported a wide variety of faunas including many types of

marsupials, crocodiles, flamingoes and even freshwater dolphins.

These early kangaroos were tiny (about the size of a rabbit) and are believed to have

descended from arboreal (tree dwelling) ancestors.

The Musky-rat kangaroo, which lives in the rainforests of north Queensland, still retains this

way of life.

By the middle of the Miocene some 10-12 million years ago, Australia began to warm up. As

time progressed and Australia moved further north, aridity (dryness) increased and rainfall

became seasonal. Forests began to change and were dominated by eucalypts with some

pockets of open forests and grasslands thriving in the drier conditions. Kangaroos became

abundant, evolving to take advantage of the variety of new environments emerging from these

changes.

They dominated these emerging grassland areas, increasing in size and rapidly diversifying.

The kangaroo fossils of this age show some evidence of hopping. The fifth toe, which is an

adaptation to an arboreal way of life, has been lost. This can be seen in the diagram of the

fossils showing the paw and toes of a middle Miocene kangaroo.


0

3cm

A B

Kangaroo fossils of the middle Miocene showing the paw on the left and toes adapted for hopping onthe right (A, B).

These and other fossils from this period show adaptations to a grazing mode of life. Among

some of these habitats, the modern types of kangaroo developed.

During the Pliocene period, 5–2 million years ago, the continent continued to dry out at a

faster rate. Rainforests became restricted to the coastal regions of Victoria, NSW and

Queensland. In central Australia and some coastal areas, woodlands and grasslands had

replaced the rainforests.

The following drawing of a fossil shows the side and top view of kangaroo molars. Scientists

say that they are an adaptation to grazing.

molar

0 3

cm

A

B

molar

molar

Top and side view of Pliocene fossil, showing molars adapted to grazing.

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By the end of the Pliocene and early Pleistocene times, conditions were even drier than today.

Kangaroos evolved bounding strides to take advantage of the vast grassland plains that had

taken over in the arid areas. This adaptation was to become more important as grasslands

emerged.

The Pleistocene, 1.6 million years ago to the present, saw the evolution of vegetation that

gave rise to the flora that dominates the continent today. Ice ages were a feature of this period

of time. Effects on the Australian environment were not as dramatic as in the Northern

Hemisphere but they did influence sea levels, which may have fluctuated some 200 metres.

This is significant when considering land bridges, especially to the north.

This was the time when the well known marsupial megafauna had evolved. Kangaroos were

at their most diverse. They varied from the giant kangaroos to small types, being adapted to a

variety of environments. As the drying continued, adaptations to overcome long periods of

drought evolved.

Giant kangaroos, wallabies and wombats and the huge Diprotodon would have been quite a

familiar sight among the first humans when they arrived some 40 000 to 60 000 years ago.

Their presence is believed to have influenced the demise of the megafauna. The Aboriginal

practice of burning further changed the vegetation and favoured grazing species.

European settlers have been responsible for further extinctions, both because of hunting and

through habitat destruction.

Case study 2: Southern Antarctic Beech

Forests dominated by southern Antarctic Beech, Nothofagus fusca, persisted in coastal regions

of the Antarctic continent until the late Oligocene. They co-existed with the emerging glaciers

(similar to the way they exist today in southern Chile) until Antarctica froze over completely.

0

90

0

SouthAmerica

Africa

India

AustraliaAntarctica

New Guinea

New Zealand

0S

Distribution of Nothofagus during the Oligocene.

The diagram following shows the distribution pattern of the Southern Antarctic Beech

(Nothofagus) as it is today. It is found in rainforests in Tasmania and in the south-eastern

Australian mainland. There are also populations in New Zealand, New Caladonia and New

Guinea and also on the southern tip of western South America.


tor

New Guinea

New Caledonia

New Zealand

Antarctica

South America

Australia

Present day distribution of Nothofagus.

Fossil records and the modern distribution pattern of the Southern Beech (Nothofagus) show

that it originated on the outer edge of Gondwana during the late Cretaceous period, around 70

million years ago.

Theories about evolution

For thousands of years, people accepted that living things never change. There was no need

to explain evolution until the evidence that creatures have changed became overwhelming.

Leonardo Da Vinci (1452–1519)

Leonardo made geological and palaeontologic observations of rocks and fossils found in

north Italy. The fossils were mostly of Cenozoic molluscs found on the tops of mountains.

Leonardo hypothesised these shell fossils had once been living things and that they had been

buried at a time before the mountains were raised.

It must be presumed that in those places there were sea coasts, where all the shell were

thrown up, broken and divided.

Leonardo’s contribution to our understanding of life was to suggest that fossils indicated the

history of the Earth far beyond human records.

Robert Hooke (1635–1703)

Robert Hooke observed fossils with a microscope and concluded that shell-like fossils really

were ‘the shells of certain shell-fishes.’ He also observed that many fossils represented

extinct organisms. Palaeontology had become the science that can be used to help understand

the history of life on Earth.

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George-Louis Buffon (1707–1778)

George-Louis Buffon published Les Epoques de Ja Nature (1788), where he suggested that

life was much older than 6 000 years as suggested by the Bible. In his 44 volume publication,

Histome Naturelle, Buffon questioned the Church’s doctrines by proposing that organisms

changed. He did not suggest how but noted that the environment acted directly on organisms.

Buffon goes down in history as having paved the way for others.

Carolus Linnaeus (1707–1778)

A Swedish botanist who was the founder of the binomial (two name) system contributed to

evolution by suggesting that species in a genus have arisen through hybridisation. This is

where two different individuals produce a new kind of offspring.

He originally fought the idea that species had changed and believed they were all created in

the beginning and none had become extinct. Later in life, he showed that his ideas were

changing.

Erasmus Darwin (1731–1802)

A leading eighteenth century intellectual and naturalist, Erasmus Darwin formulated the first

modern theory of evolution in his book, The laws of organic life.

Describing how one species could evolve into another, he suggested that sexual selection and

competition could cause changes in species.

He wrote:

the final course of this contest among males seems to be that the strongest and most active

animal should propagate the species which should thus be improved.

He also helped to introduce the concept of adaptation by saying that organisms are fit for the

environment in which they live and that their structure reflects the functions they perform

throughout their lives.

Jean-Baptiste de Lamarck (1744–1829)

Lamarck is always associated with the discredited theory of evolution where features

‘acquired’ throughout an individual lifetime are inherited by offspring. Lamarck proposed

that an organism develops features by use or disuse throughout its lifetime. For example, a

giraffe develops a long neck by stretching to eat the leaves of tall trees. This acquired feature

is then passed on to its offspring.

Although wrong, Lamarck’s ideas did pave the way for natural selection and made a major

contribution to the development of evolutionary thought.

Sadly his theories were ignored and Lamarck died a poor man.

His colleagues even used the eulogy at his funeral to discredit him.


Alfred Russel Wallace (1823–1913)

Just north of Australia, through the middle of Indonesia and between the islands of Borneo

and Sulawesi, is an imaginary line. This line separates the islands of Bali and Lombok and is

called the Wallace line.

Biologists use this line to describe the separation of Australia flora and fauna from Asian flora

and fauna. It was named after Wallace because of the observations he did in this region. It

was in Indonesia that Alfred Wallace concluded that species evolved by a process called

natural selection. He wrote to Charles Darwin.

Charles Darwin had independently arrived at the same conclusion after his extensive

observations and work at the Galapagos Islands. The theory of natural selection was actually

proposed by Wallace but has historically become known as the Darwin/Wallace theory of

natural selection to incorporate the work done by Charles Darwin.

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Part 1: Evolution

Charles Darwin (1809–1882)

Charles Darwin was a founder of modern biology and author of the famous book, On the

origin of species. He suggested that plants and animals in nature produce far more offspring

than can survive. Each individual has its own variety of features. There is a continual

struggle for existence. Those individuals with variations that increase their chance of survival

(the fittest) reproduce more. Hence, this interaction between a variety of individuals and the

harsh environment is the direct cause of change in species and explains evolution.

Charles Darwin was aware of the social and political upheaval his ideas may cause. He did

not publish his famous book about evolution for almost 25 years, until Wallace suggested the

theory, and Darwin felt more confident about presenting his observations and thoughts.

Viewpoints about evolution

From the time that the theory of evolution was first presented, it has met with opposition and

misunderstanding. People have tended to react to it emotionally and philosophically, rather

than assessing it as a scientific explanation that seeks to best explain available evidence.

The theory of evolution does not attempt to undermine religious beliefs or ideas about the

worth of people. Instead, these are non-scientific arguments that are separate from the debate

about whether the theory of evolution is supported by sufficient scientific evidence and

whether it is, indeed, the best explanation of that evidence.

The theory of evolution has continued to develop and be refined throughout the twentieth

century, as more and more evidence has been collected. The theory will continued to be used

and examined into the twenty first century because it remains, to date, the best scientific

explanation of many observations of changes in living things, both past and present.

Here are some examples of social and political thinking about evolution for you to evaluate.


Example 1: Cartoons

Cartoons are a common way that social comment is made in newspapers and magazines.

There have been many cartoons drawn about evolution. Some show organisms slowly

changing form over time. For example, look back at the cartoon in the introduction to this

part.

Other cartoons were drawn to ridicule evolutionists. (And some have been drawn to ridicule

people who oppose evolution too.) A famous cartoon from the 1800s shows Charles Darwin

looking like an ape.

From "Darwin as an Ape." Cartoon. 1871.

Example 2: A view of a nineteenth century scientist

What is man? A profound thinker, Cardinal de Bonald, has said, ‘Man is an intelligence

assisted by organs.’ We would fain adopt this definition, which brings into relief the true

attribute of man, intelligence, were it not defective in drawing no sufficient distinction

between man and the brute. It is a fact that animals are intelligent, and that their intelligence

is assisted by organs; but their intelligence is infinitely inferior to that of man.

…whence comes man? Wherefore does he exist? …the problem is beyond the reach of

human thought. …but it will be sufficient for our present purpose to say that it can be shown

that man is not derived, by a process of organic transformation, from any animal, and that he

includes the ape not more than the whale among his ancestry; but that he is the product of a

special creation.

…Let us say that the creation of the human species was an act of God, that man is one of the

children of the great Arbiter of the universe, and we shall have given to this question the

only response which can content at once our feelings and our reason.

Louis Figuier in his nineteenth century book, The human race.

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Part 1: Evolution

Example 3: A modern view

You may be able to borrow a book by Stephen J Gould that includes information about some

of these social and political influences.

You could also look at some of the many Internet sites on this subject.

You’ll find plenty of information in favour of and opposed to the theory of

evolution. You will find some helpful starting points on the Science online

webpage at: http://www.lmpc.edu.au/science


Suggested answers

Adaptations to suit environments

Changes in the environment put pressure on the species living there. Species with features

that enable them to survive will thrive and reproduce while those without the adaptations for

survival become extinct.

Earth’s constantly changing environment1 Features of the environment that may change include:

• available water – wetter or drier

• temperature – hotter or colder

• pH – more acidic or more alkaline

• available space - less space or more space

• concentration of dissolved minerals

• introduction of a new more competitive species

• competition from members of the same species.

2 Some other features are also included in the following table.

Physical Chemical Changes to competition

• changes intemperature

• changes inpressure

• changes inlight

• availability ofgases such asoxygen orcarbon dioxide

• changes to pH

• changes tosalinity

• predatory competition introductionof prey/predator

• lack of space

• competition from members of thesame species

• disease

3 a) Adaptations for an area drying out include: a skin coating or cover to prevent

desiccation, more concentrated urine and less surface area of leaves in plants.

b) Adaptations for a new species of poisonous frog include: resistance to the poison and

seeking alternative food sources.

c) Adaptations for increased salinity include: the ability to absorb water by active

transport and the ability to excrete salt as a waste.

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Part 1: Evolution

The fossil record of horses



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1 They have descended from a common ancestor and did not give rise to one another at the

same time.

2 The span is becoming longer in length.

3 There is diversity in the teeth span: some less, some more.

4 They may have originated from the same ancestor as Miohippus.

5 There are many valid interpretations.


6 Here are two possible alternative answers.

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6 To decide which graph is best (yours or either of the ones above), you would need to use

data from other characteristics of these organisms, not just the span of their cheek teeth.

Your answers for the following questions depend upon how similar your graph is to the ones

shown.

7 4 cm

8 About 10.5 cm

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Part 1: Evolution

9 The horse evolves slowly at first, then, after a series of rapid diversifications, evolves

quickly.

10 Many organisms don’t preserve very well. Life forms, as recorded in fossils, are still

only a fraction of the number that have ever lived. We are only just finding new

techniques for determining the makeup of past life forms. With further development in

these areas, more knowledge will be obtained.

Transitional fossils

Scientists want to find the steps that led from one life form to another. Although most

modern scientists do not expect to find real transitional forms – in between organisms – they

continue to search for evidence of evolution.

Biogeography as evidence for evolution

The borders of the biogeographic zones are oceans and mountain ranges.

Wallace’s line

Most vertebrates, apart from birds and bats, are restricted to regions bordered by coastlines

and mountain ranges. Flowering plants have dispersal methods which enable them to be

distributed beyond these limiting barriers.

Six degrees of separation

In order from most different to least different are: 1 Australian (8), 2 Ethiopian (6), 3

Neotropical (5.3), 4 Nearctic (1.3) and Oriental (1.3), and 6 Palaearctic (0.6).

Comparative embryology

The middle row is the most similar.

Biochemistry1 a) chimpanzee

b) yeast

2 The more closely related the species, the fewer number of amino acid differences.

Other evidence – divergent evolution1 Amphibians reproduce in water and their early stages of development require a life in

water.

2 Insects and other arthropod groups could live inland.

3 Dinosaurs reproduced by internal fertilization and laid eggs.

4 Ecosystems left vacant by the perishing dinosaurs enabled mammals to diversify and

establish themselves in new specialised niches. They had plenty of food and little

competition for resources.


5 Divergent evolution is when one group or species evolves into two or more groups to

occupy new niches.

Convergent evolution1 The physical feature that they all have is a streamlined body. This is an adaptation for

overcoming the viscosity of water.

2 Moving about through water swiftly is important for the survival of these animals.

Natural selection has selected animals which have evolved to this shape so these very

different animals look much the same.

The evolution of evolution

Politics was centred around the beliefs of the church. Alternative explanations were against

the dogma of the church; therefore they challenged the establishment.

Accepting an idea such as evolution of species required people, including scientists, to sort

through many issues, including what science is, what religion is and why human society is

organised in particular ways.

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Part 1: Evolution


Exercises – Part 1

Exercises 1.1 to 1.7 Name: _________________________________

Exercise 1.1: Earth’s constantly changing environmenta) List some physical conditions that might change in the environment.

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b) List some chemical conditions that may change in the environment.

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c) How might these changes impact on the evolution of plants and animals? Choose two

physical changes and two chemical changes that you have listed and outline their effects.

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Exercise 1.2: An open-ended investigation of natural selection

Describe an open-ended investigation that you have done that illustrates natural selection.

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Part 1: Evolution

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Exercise 1.3: A case study

Name of Australian species studied: ___________________________

Describe changes in this species that have occurred over time because of environmental

changes.

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Exercise 1.4: Wallace’s line

The Wallace line falls between Borneo and Sulawesi and between the tiny islands of Bali and

Lombok. The latter pair of islands is separated by a mere 30 km, but for the most part they

are inhabited by different families of mammals and even different birds.


Australia

0 1000 km

Irian Jaya

Australia

Ph i l ipp ines

Sumbawa

P a c i f i c O c e a n

B a n d a S e a

Timor

Gulf ofCarpentaria

Flores

Borneo

A r a f u r a S e a

T i m o r S e a

C e l e b e sS e aSabah

PapuaNew Guinea

Halmahera

Sulawes i

Limit of nat ive placentalmammals other than bats,Muridea, Sus and Cervus

Limit of marsupialsW

all

ac

e’s

Lin

e

a) How would you account for these differences?

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b) How did these observations influence Wallace to propose his theory of evolution?

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Exercise 1.5: Comparative anatomya) Compare the finger bones labelled 1, 2, 3, 4 and 5 for a bat, human, whale, lizard, cat,

frog and bird by filling in the following tables. The first entry in each table is done for

you.

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Part 1: Evolution

humerus

ulna

radius

carpal

1

234

5

Lizard

Human

humerus

ulnaradius

carpal

1

2 34

5

Bat

1

2

3

4

5

humerus

ulna

radius

carpal

Bird

humerus

ulna

radius

carpal

1

23

Cat

humerus

ulna

radius

carpal

1

23 4 5

Frog

humerus

ulnaradius

carpal1

2

3

45

Whale

humerus

ulnaradius

carpal

1

2

3

4

5

Fingerbones of vertebrates.


Organism Fingerbone present ( ) or absent (x)

1 2 3 4 5

frog

lizard

bird

cat

bat

whale

human

Analyse how the structure is related to the function of each by filling in the following table.

Organism Function of limb

frog limb used for support and cleaning

lizard

bird

cat

bat

whale

human

b) Compare the structure of the pentadactyl limb for three of the above vertebrates.

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c) How would an evolutionary biologist explain the pentadactyl features?

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Exercise 1.6: Other evidence

Describe how the finches of the Galapagos Islands are an example of divergent evolution.

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Part 1: Evolution

Exercise 1.7: The evolution of evolutiona) Do your own research on the historical development of theories of evolution. You can

also use the material in the Additional resources section titled ‘Theories about

Evolution’. Present your information in the table below.

Identify the data source(s) you used.

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Name of scientist Dates Contribution

Leonardo Da Vinci

Robert Hooke

George-Louis Buffon

Carolus Linnaeus

Erasmus Darwin

Jean-Baptiste de

Lamarck

Alfred Russel Wallace

Charles Darwin

b) Do your own research on social and political influences on the development of the theory

of evolution. (You can also read the information in the Additional resources section.)

How do you think social conditions and political ideas have affected the development and

acceptance of an evolutionary explanation for life on Earth?

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