1. Evolution © Alan Richardson
The Chalk cliffs at Birling gap (East Sussex). The chalk was formed 100 million years ago, mainly from miniscule, finely sculptured chalky plates that enclosed the bodies of single-celled algae living in the plankton at that time.
© Alan Richardson

2. The theory of evolution offers an explanation for the existence of 2
The theory of evolution offers an explanation for the existence of
all living organisms on the Earth today and in the past
It supposes that present day organisms have all been derived
from organisms that lived in the past
By a series of very small changes over millions of years new
species have developed from previous species*
Over a period of about 3000 million years, many new species have
been produced and many have become extinct.
* In some cases it appears that evolution proceeded by periods of rapid change, interspersed with periods of little or no change,
We know a great deal about the organisms that lived millions
of years ago from studying their fossilised remains.
Theory of evolution

3. 3
Fossil formation
There are many ways in which an organism can be fossilised
One of these ways is shown in the next sequence of slides
In principle, a fossil is formed when an organism dies, its body is
enclosed in mud, or sand. The soft parts decay but some of
the hard parts (skeleton, shells, seeds) are preserved
The mud or sand eventually becomes rock and the hard parts of the
organism are mineralised.
Sometimes an organism dies in a situation which prevents its decay (e.g. being overwhelmed by a mud deposit). In this case the soft parts are often preserved as fossils and can be studied by cutting sections through the fossil. Whole organisms may be preserved in ice.
When the rock is exposed as a result of earth movements or erosion,
the fossil remains can be dug out and studied.

4. Process of fossilisation4
The sediment eventually becomes rock
Fish B becomes a fossil much later than fish A
The deeper the rock layer, the older the fossil
Living fish B
Dies
Enclosed in sediment
Hard parts fossilised
Living fish A
Dies
Enclosed in sediment
Hard parts fossilised
Process of fossilisation

5. fish skeleton partly buried by sediment5
living fish
sediment from river
fish skeleton partly buried by sediment
Sedimentation

6. more recent sediment collects6
more recent sediment collects
older sediment
becomes rock
fish skeleton fossilised
Layers of sediment

7. Earth’s crust movement7
land raised above
water level
recent rock
older rock
Earth’s crust movement

8. fossilised skeleton exposed8
fossilised skeleton exposed
earth movements
fracture rock
Fractured rock

9. When rock strata become exposed, it can be assumed that, 9
When rock strata become exposed, it can be assumed that,
in most cases, the lowest layers are the oldest*
This means that the fossils of organisms preserved in the lowest
layers represent animals and plants that lived many millions
of years ago
rock strata of
increasing age
Rock strata exposed at a cliff face. Each layer represents millions of years of deposition.
* The movements of the Earth’s crust may cause the strata to become distorted. Sometimes the strata are vertical or even turned upside down with the oldest rocks appearing on top. It is usually possible to tell when this has happened.
© Alan Richardson
Rock strata

10. This is a fossil of a fish which lived 40 million years ago10
This is a fossil of a fish which lived 40 million years ago
A fossil fish (Mioplosus labracoides) from the Eocene era (30 –50 million years ago.The fossil is obviously that of a fish, but the species is not represented among present day fish
© Alan Richardson
Fossil fish

11. Fossil fish reconstruction11
This is a reconstruction, from fossil remains, of an ‘armour-plated’
fish which lived 350 million years ago
dorsal fin
The fish which gave rise to fossils such as this, were very
different from today’s fish
Fossil fish reconstruction

12. By studying the type of fossils and the abundance of each species 12
By studying the type of fossils and the abundance of each species
in the different strata, it is possible to build up a picture of how the
populations of organisms changed over millions of years
The next slide shows how this picture appears for vertebrate animals
The width of each band represents the relative abundance of
the organisms as judged by their fossil remains.
For example, 100 million years ago there were many more species
of reptiles than there are today
Mammals do not appear at all in rocks older than about
3 million years
Vertebrate sequence

13. Vertebrate fossil record13
Relative number of species
mammals
birds
100 million
years ago
reptiles
amphibia
200 million
years ago o
fish
300 million
years ago
400 million
years ago
Possible lines of evolution
Vertebrate fossil record

14. Interpretation of the fossil record (1)14
Interpretation of the fossil record (1)
In interpreting the fossil record, it must be borne in mind that
fossils will be formed only in places and at times when conditions
are suitable for fossilization. So they may not be representative of
the organisms living at that time 1
only the skeletons, shells and other parts resistant to decay will
be preserved 2
fossils are found only if they are exposed by Earth movements or
erosion 3
1 A local flood may engulf a community of animals which are not abundant elsewhere.
2 There may be many soft-bodied organisms and non-woody plants living at that time which do not form fossils.
3 There may be millions of fossils lying undiscovered that might put a different interpretation on the kind of organisms living in the past.
4 If organisms were gradually changing, you might expect to find fossils remains showing intermediate stages in the change
very few fossils have been found which show intermediate
stages between different groups of organism 4
Interpretation (1)

15. Interpreting the fossil record (2)15
Interpreting the fossil record (2)
Despite its gaps, the fossil record does show that, over millions
of years,
organisms became more numerous and more diverse,
i.e. many more species came into existence 1
organisms became more complex 2
although very few organisms found as fossils are alive today,
there are many basic similarities in the body structure of the
fossils and similar organisms living today 3
1 For example, 500 million years ago (mya) there were no vertebrates; 350mya there were no reptiles;
200mya there were no birds
2 For example a fish is a more complex organism than a sea anemone
3 For example, fossil remains of fish are unmistakeably similar to present day fish. (See slides 10 & 11)
4 The classic example is Archaeopteryx which has features common to both birds and reptiles
There are many mammal-like reptiles in the fossil record and recently a fossil has been found that is intermediate between a fish and a land animal
although they are few, there are fossils which show characteristics
intermediate between major groups4
Interpretation 2

16. Replica of Archaeopteryx fossil; half bird half reptile16
claws
wing-like
forelimbs
teeth
thin
ribs
long tail
feathers
Replica of Archaeopteryx fossil;
half bird half reptile
© Alan Richardson
Reptile-like features
Bird-like features

17. Evidence from comparative anatomy18
Evidence from comparative anatomy
Fish, amphibia, reptiles, birds and mammals all have vertebral columns, skulls, brains, circulatory systems and many other features in common
This suggests that they all arose from a common ancestral form rather than arising independently.
The same reasoning can be applied to other groups of organisms such as insects which have most of their anatomical features in common
Although these features are superficially different there is a basic pattern underlying them all
Comparative anatomy

18. 17
Vertebrate limbs
The basic pattern of the vertebrate limb is represented by the human arm skeleton shown below
group of small bones
ball and
socket joint
hinge joint
single bone
two bones
five jointed digits
Vertebrate forelimb

19. The basic pattern suggests they have evolved from a common ancestor19
The forelimbs of the following vertebrates show the basic pattern of limb bones with modifications which are adapted to their methods of locomotion.
The basic pattern suggests they have evolved from a common ancestor
Lizard
Bird
Dolphin
Bat
Modified limbs

20. 20
DNA evidence
Another important line of evidence for evolution comes from DNA analysis
Any permanent change in form or function of an organism must be preceded by a change in its DNA
Organisms which have much of their DNA in common must be closely related, i.e. they have split from a common ancestor comparatively recently (in geological terms)
For example, humans and chimpanzees have 99% of their DNA in common which suggests a close relationship and relatively ‘recent’ divergence from a common ancestor
DNA evidence

21. Evolutionary pathways21
Evolutionary pathways
The next slide shows the widely accepted pathway of evolution for plants and animals
Only a few of the main types of organisms are shown

22. Evolutionary pathways 2
Monocots
Herbs
Shrubs
Trees 22
Mammals
Birds
Reptiles
Conifers
Amphibia
Dicots
Fish
Flowering plants
Mosses
Insects
Ferns
Crustacea
Liverworts
Annelids
Flatworms
Mollusc
Algae
Fungi
Coelenterates
Multicellular
plants
Multicellular
animals
Single celled
organisms
Evolutionary pathways 2

23. Mick. ‘What were we before that?’23
Dave. ‘A bloke on the telly just said that before we were humans we were monkeys’.
Mick. ‘What were we before that?’
Dave. ‘ I don’t know. I can’t even remember being a monkey’
Dave and Mick

24. Incorrect evolutionary sequence24
Dave is wrong
Dave’s view of evolution
Incorrect evolutionary sequence

25. 25
Dave seems to think that evolution can take place in a person’s lifetime. This is pretty bizarre, even for Dave.
He has also confused monkeys with apes. Our nearest relatives are apes (chimpanzees and gorillas), not monkeys
He makes the common error that, e.g. fish, as we know them today gave rise to amphibia and, by the same reasoning, apes, as we know them, gave rise to humans
The correct interpretation of the evidence is that apes and humans had a common ancestor which was neither ape nor human
In the course of evolution, this common ancestor produced two lines of descendants, culminating in modern day humans and modern day apes
Discussion

26. ‘Correct’ evolutionary sequence26
The accepted view of evolution
‘Correct’ evolutionary sequence

27. Question 1 Evolution has taken place over (a) hundreds (b) thousands28
Question 1
Evolution has taken place over
(a) hundreds
(b) thousands
(c) millions
(d) billions
of years

28. Fossils can be formed only if total decay29
Question 2
Fossils can be formed only if total decay
(a) is prevented
(b) is accelerated
(c) is slowed up
(d) is immediate

29. Question 3 Older fossils are found (a) in the deepest rock layers30
Question 3
Older fossils are found
(a) in the deepest rock layers
(b) in the shallowest rock layers
(c) only in rocks over 1 million years old
(d) evenly dispersed in all rock layers

30. (d) are never related to other fossilised organisms31
Question 4
Which of these statements is correct ? Fossilised organisms
(a) are all totally different from present-day species
(b) are much the same as present-day species
(c) often show strong resemblances to present-day species
(d) are never related to other fossilised organisms

31. (a) Birds and mammals; reptiles; amphibians; fish32
Question 5
The order of appearance of vertebrates in the fossil record is
(a) Birds and mammals; reptiles; amphibians; fish
(b) Fish; amphibians; reptiles; birds and mammals
(c) Fish; reptiles; amphibians; birds and mammals
(d) Amphibians; fish; reptiles; birds and mammals

32. Reptiles were most abundant33
Question 6
Reptiles were most abundant
(a) 400 million years ago
(b) 300 million years ago
(c) 200 million years ago
(d) 100 million years ago

33. 34
Question 7
Archaeopteryx is a fossil which shows features intermediate between
(a) reptiles and mammals
(b) reptiles and birds
(c) birds and mammals
(d) reptiles and amphibians

34. Question 8 Which statement is correct ?35
Question 8
Which statement is correct ?
(a) Amphibia are derived from fish
(b) Amphibia evolved into reptiles
(c) Amphibia and fish share a common ancestor
(d) Reptiles evolved into mammals

35. 36
Answer
Correct

36. 37
Answer
Incorrect