Emp 1003 Evolution

2
There are innumerable varieties of lifeforms on Earth.

3
Possible answer:
All living things were created
at the same time in their
current form.
Basis: traditional biblical
interpretation.

4
Possible answer:
Different types of living things were created at different
times.
Basis: modified biblical interpretation

5
Possible answer:
Different types of living things
evolved from earlier types.
Basis: science
Evolution of whales

6
This presentation consists of six sections:
1. Evolution of Evolutionary Thought
2. Charles Darwin
3. The Theory of Evolution
4. Mechanisms of Evolution
5. Types of Evolution
6. Evidence of Evolution

8
Anaximander (c.610 BC–c. 546 BC)
A Greek philosopher who thought that the
universe was originally in a state of chaos
from which came all creatures.
Mankind sprung from some other species of
animals, probably aquatic, through
‘transmutations’ (i.e. changes).
For this, some people consider him to be
evolutionary theory's most ancient proponent.

9
Aristotle 384-322 BC
The father of animal biology, he established
basic principles of classification.
He believed that organisms were created
separately but developed from simple ones to
others ever more complex: continuity of
organization and unity of plan.
He developed the idea of the Scala Naturae
known also as the ‘Great Chain of Being’ (see
slides 10-12)

10
The Great Chain of Being or Scala
Naturae is a classical and western
conception of the order of the universe,
whose chief characteristic is a strict
hierarchical system.

11
The idea was accepted by most educated men from Roman
times until the Renaissance. It is composed of links, from the
most base elements up to the very highest perfection: God.
Perfection (God)
Angels
Humans
Beasts
Plants
RocksThe concept of "animal, vegetable, and
mineral" still survives and, importantly,
made up the "three kingdoms" of
Linnaeus's taxonomic system.

12
Two illustrations of the
Scala Naturae
proposed by Aristotle,
showing a passage from
the simple to the
complex and from the
base to the sublime.

13
Epicurus 341-270 BC
Believed he world has endured for an infinite
time and life developed without divine
intervention. He formulated the beginnings of a
theory of natural selection in evolution.
e.g.: “Many races of living things must have died out and
been unable to beget and continue their breed. For, in the
case of all things, either craft or courage or speed has
from the beginning of its existence prohibited and
preserved each particular race”.

14
Pliny the Elder 23-79 AD
A Roman scholar who was a “Natural
Philosopher” and wrote Naturalis
Historia, an encyclopedia of 37 books
dealing with subjects like geography,
biology, agriculture, anthropology,
mineralogy and other topics.
He described in detail what today would
be called biodiversity.

15
Matthew Hale (1609- 1676) was an English
judge and writer who is credited with having coined
the word ‘evolution’.
The word comes from the Latin word "evolutio",
meaning to "unroll like a scroll".

16
Ironically, Hale coined the
word evolution in a book he
wrote in 1677 to deny its
existence and to attack what
he called the ‘atheist’ ideas of
Epicurus and other classical
Greek thinkers. (slide 13)

17
With time however, there were some facts which came to
light and which seemed to challenge the idea of a world that
was unchanging since Creation.
One of these was the discovery of fossils.

18
It seemed obvious that there existed animals which were
different from those inhabiting the known world.
For a long time, these vaguely reptilian fossils were
explained as the remains of dragons and other mythological
creatures.

19
Dinosaur fossils had been known for
centuries as "dragon bones" or the
remains of giants.

20
Elephant and mammoth skulls had also been thought
to belong to a race of one-eyed giants which,
supposedly still existed, since even the concept of
extinction was not accepted widely.

21
It wasn't until Dean William Buckland of
Oxford, described the carnivorous
"lizard" Megalosaurus (in 1824) that
“dragons” were formally studied as an
extinct group of giant reptiles.
Megalosaurus
Dean
William
Buckland
1784 - 1856

22
Even though Buckland’s
reconstruction was incorrect
he still has the great merit of
“discovering” dinosaurs.

23
Georges-Louis Leclerc, Comte de
Buffon (1707- 1788)
A French naturalist who influenced the next
two generations of naturalists, including
Lamarck, Wallace and Darwin, among
others.
(see slides 32 – 43)

24
His Histoire naturelle, générale et
particulière (36 volumes) included
everything known about the natural
world.

25
Buffon considered the similarities between humans and
apes, and the possibility of a common ancestry.

26
Buffon observed that some animals
retain parts that are vestigial and no
longer useful, suggesting that they
had evolved
rather than been
created
individually or
generated
spontaneously

27
Rev. Thomas Robert Malthus
(1766 - 1834)
Malthus was not a naturalist but an
economist who was interested in the way
that human populations regulated
themselves.
He is included here because his ideas had
a great influence on the development of
evolutionary thought.

28
He was responsible for the
concept of the struggle for
survival, or natural selection,
upon which theories of
biologists* later depended.
* including those of Spencer,
Darwin and Wallace

29
Georges Cuvier (1769-1832) proposed
the concept of what later became known
as Catastrophism, (the term itself was coined
later) which suggested the occurrence of
many violent supernatural catastrophes
that had occurred on earth since its
creation.

30
Each catastrophic event had wiped the earth clean of many
living creatures.
The survivors of these events then continued on - perhaps
with the aid of newly created animal species.

31
Although this theory is now known to be incorrect,
Cuvier has the merit of being one of the first to state
that species can become extinct.

32
Jean-Baptiste Lamarck (1744 - 1829) a
French naturalist, one of the first to use the
term biology in its modern sense.
He was an early proponent of the idea that
evolution occurred and proceeded in
accordance with natural laws.

33
Lamarck believed in spontaneous generation, with the
simple organisms thus created changing over time and
becoming gradually more complex and closer to
perfection as they evolved.

34
Lamarck is remembered today mainly in connection
with a discredited theory of heredity, the "inheritance
of acquired traits".
This theory states that if an
organism changes its shape
during its lifetime (i.e. acquires
new characteristics), these
changes will be carried on to
future generations.

35
Lamarck developed two laws:
1. Frequent use of any body structure strengthens, and
enlarges that structure while its permanent disuse weakens
it until it finally disappears.
2. All changes
acquired during
the lifetime of an
organism are
passed on to the
offspring.

36
Summary of Lamarck's evolutionary theory:
• Organisms progress towards “higher” forms
• Development follows desire or “will” use/disuse
• This leads to replacement or
extinction of organs
• “Acquired characteristics” are
passed on to offspring.
• Parallel evolutionary chains
are possible

37
1. Early giraffes had short necks that they stretched for
food
2. The longer necks were passed on to their offspring,
who then stretched them more
3. Eventually only long-necked giraffes existed
1 2 3

38
Wallace was an Englishman who
came from a family of modest
means.
He received a limited education,
worked many jobs: construction,
surveying, assistant, watchmaker,
teacher, and others
Alfred R. Wallace
1823 - 1913

39
Wallace loved natural history and
the outdoors. He travelled to
Brazil with Henry Bates, another
naturalist, and explored the
Amazon.
During this voyage he collected
and sold large numbers of
biological specimens, especially
insects.
Alfred R. Wallace
1823 - 1913

40
1848: Wallace and Bates
sailed for South America
and gathered large
collections of specimens.
Artist’s impression of Henry Bates
exploring the Amazon

41
1854: Wallace studied the
fauna of the Malay
Archipelago and realised
that the area was divided
biologically by a narrow
strait, separating Asian from
Australasian fauna.

42
This boundary is still
known as Wallace's
Line.
It lies just east of
Borneo, marking the
boundary between the
Asian and the
Australasian faunas.

43
Wallace applied the geological idea of Uniformitarianism to
biology.
This is the idea that the natural processes that have
operated in the past are the same that operate today and
apply everywhere in the universe

44
The term was coined in 1832 by William
Whewell who also coined the term
Catastrophism to define the religious idea
that life on Earth was periodically subjected
to catastrophes and re-created every time.
The idea had actually been conceived first
by James Hutton (right), a Scottish
geologist, in the late 18th century.

45
who supported Hutton’s idea that the earth was shaped by
slow-moving forces still in operation today.
Lyell was a geologist

46
Uniformitarianism implies that layers of silt and sand
are laid down slowly
and uniformly over long
periods of time.
These layers cover
dead creatures slowly
turning them into
fossils.

47
This gave an idea how fossils
were formed and showed how
organisms developed through
time.

48
As sediments are laid down chronologically, the
fossils found in
lower layers are
older than those
found in layers
above them.

49
Wallace also realised that the
classification chart of a species might
look more like a tree than a straight
line.
No species came into existence unless
it was derived from another similar one
that was its predecessor.
The tree of human evolution according to the
biologist Haeckel (1891)

50
In 1855, Wallace anonymously
wrote a paper, “On the Law Which
Has Regulated the Introduction of
New Species”,
arguing that some kind of evolution
of species must have occurred and
searching for a mechanism (the
same thing that Darwin was
saying).

51
In this he was inspired by the
work of Malthus, a British
economist.
In An Essay on The Principle of
Population (1797), Malthus had
observed that most organisms
produced far more offspring than
could possibly survive.

52
When resources are plentiful, the
size of a population tends to
increase until it outstrips its food
supply.
This led Malthus to believe that
poverty, disease, and famine were
a phenomenon of nature, leading
to a "struggle for existence".

54
Born in England, son of a wealthy doctor,
he studied medicine but dropped out, then
tried theology, but was much more
interested in natural history.
Charles Darwin
(1809-1882)

55
After university, Darwin signed on as unpaid ‘naturalist’ on the
Royal Navy ship Beagle and took a 5-year trip around the
world (1831-1836).

56
The ship’s mission was to map the coast of South America, but it
travelled around the world, including the Galapagos Islands, of
volcanic (hence recent) origin off the coast of Ecuador.

57
Darwin was struck by the diversity of animals
on the Galápagos Islands.
He thought of adaptation to the environment
and the origin of new species as closely related
processes.
As populations, separated by a geographic
barriers, adapted to
local environments,
they became
separate species.

58
During the voyage Darwin noted many things that suggested
evolution must have taken place. These observations, taken
together, suggested that species change over time, i.e. evolution
occurs.

59
South American fossils resembled living animals.
Glyptodont (2000 kgs)
is a fossil mammal that
looked like the modern
day armadillo (2 kgs)

60
Parts of the world with similar
climates (e.g. South America,
Australia) have very different
organisms.
It did not seem to make sense if
the organisms were created.
Why create different animals for
similar climates?

61
Two dog-like
medium-sized
predators filling
the same
ecological niche: a
marsupial (left) and
a placental (right).

62
Meanwhile certain plants and animals on each
continent are different and distinctive and found
only there.

63
Many species on oceanic islands are
found only there (endemic). Often
groups of very similar species are
found on these islands.
e.g. Galapagos iguanas and finches.

64
On Galapagos Islands there are 13 species of anatomically very different,
but closely related species of finch. They differ greatly in beak size and
diet, having evolved very different lifestyles.

65
Darwin asked himself why there
was such tremendous diversity
among these small birds.
Why did they have physical
similarities to the mainland species
but had many more forms?

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Darwin concluded that these island birds had originated from
the same species but had then adapted themselves to living in
different habitats.

67
Some 10,000 years ago a number of
small finches, probably grassquits,
made their way from South America
to the Galapagos Islands.
The small birds happened across a
landscape relatively free of
competitors. The isolated location of
the islands meant that new species
arrived relatively infrequently.

68
Geographically isolated and without competition from similar
species, these finches developed distinctive
anatomy (particularly
beak size and shape)
and behaviour, with
each species
exploiting a unique
feeding niche.

69
Bills are adapted in
different species for
different purposes, such
as crushing seeds,
pecking wood, and
probing flowers for nectar.

73
This Galapagos finch is one of the few birds
in the world to use “tools” when feeding, in
this case a twig or cactus spine. It uses
cactus spines or twigs to pry insects &
larvae from cacti or from beneath bark.

75
Besides the voyage on
the Beagle and the
observations made,
another issue
influenced Darwin:
Artificial Selection.

76
Darwin studied pigeon-breeding and
realised that the domestic types of pigeon,
which were all derived from the wild
species, had different body forms because
the breeders had selected particular birds
to produce offspring.

77
Darwin imagined a process similar to artificial selection but carried out by
nature and producing the wild organisms we see today. He called it
Natural Selection.
Darwin’s idea was based on some
preliminary generalisations, made after
he observed plants and animals both
during his Beagle voyage and in
England itself.
Tree trunks grew darker with soot from pollution. Therefore, the light-
coloured moths were more visible to predators, and since they were
more easily caught, their numbers declined. The numbers of dark
moths, however, increased. When pollution decreased, the opposite
happened.

78
Darwin’s generalisations (today accepted as true) are:
1. Individuals in species vary (random genetic differences)
2. Some of these variations are passed on (hereditable)
3. More offspring are produced that can survive each generation
(struggle for existence)
4. Survival and reproduction are not random (the favourable
variants are naturally selected)

79
When Darwin returned home he worked for many years
analysing his data.
In 1844 he wrote a long essay on the origin
of species and natural selection but did not
publish it immediately because he was
wary of the reaction it would provoke.

80
In June 1858 Darwin received a manuscript from Alfred
Wallace who had developed a theory of natural selection
similar to his own.
Darwin quickly finished his own book and published it the
next year.

81
On the Origin of Species by
Means of Natural Selection (1859)
became one of the most
influential scientific texts of all
times.
(The entire printing of 2500 copies
was sold that same day!)

82
After ‘Origin of Species’ Darwin
published various other books
including one to show the variations
that existed among domestic plants
and livestock.

84
After Darwin observed
plants and animals both
during his voyage on the
Beagle and in England itself
he reached certain
conclusions (general
assumptions) which are
today accepted as true.

85
1. There is variation in populations.
2. This variation is heritable.
3. In every generation some organisms are more
successful at surviving and reproducing than others.
4. Finally, survival and reproduction are not random,
but related to the variations among individuals.
Organisms with the best characteristics are ‘selected
by nature.’

86
This is the logical result of four
features of all living systems:
• Variation
• Inheritance
• Selection
• Time

87
Individuals in any population vary
from one another.

88
Parents pass on their traits to their
offspring genetically.

89
Some variants manage to reproduce more
than others.

90
Successful variations accumulate over many generations.

91
1. In a population individuals vary from each other –
have different characters.
2. These different characters are passed on from
parents to offspring.
3. Because of these inherited characters, certain
individuals are more successful at surviving and
reproducing than others.
4. In time, this will influence and determine the
characters of the whole population.

92
These points, taken
together are
basicallywhat evolution
is all about: descent with
change.
Important: Individuals do
not evolve, only
populations do.

94
As explained in the previous section, evolution is a
process by which populations change over time.
How does this come about?
Evolution of the camel

95
As Darwin theorised, the main stimulus to change is a
process known as Natural Selection.
We might consider it the motor, the energy, which
drives evolution.

96
We have already seen how Natural Selection works:
organisms belonging to the same population are
different from each other and the environment ‘selects’
the ones which are better suited.
The tail spines give this
stegosaurus a better chance
to survive an attack by a
predator.

97
Organisms that are best suited to their environment as
said to be “adapted” and the process known as
adaptation.
Flightless Birds
Adapted to running
Adapted to swimming

98
Among the animals seen by
Darwin at the Galapagos
were cormorants which had
lost the power of flight.

99
They had no predators from whom
they had to escape by flying and,
at the same time, the stubby wings
gave them an advantage as it
made them better swimmers (like
penguins).

100
Darwin saw the transformation of wings into “flippers” as a
case of adaptation to a particular environment.

101
The idea that the environment, or ‘nature’ as they called
it in the 19th century, has an effect on evolution was
also proposed by Lamarck but he had a different
mechanism in mind.
According to
Lamarck
According to
Darwin

102
1. Early giraffes had necks of various lengths.
2. Natural selection due to competition led to survival of the
longer-necked animals and their offspring.
3. Eventually only long-necked giraffes survived the competition.
1 2 3

104
We have seen that
“nature” selects certain
individuals who survive
and reproduce instead
of others.

105
This is a phrase which refers to the
competition for survival or dominance.
Although it is now used especially for
evolution, it was originally applied to socio-
economics by philosopher Herbert Spencer
who, in 1864, drew parallels with Charles
Darwin's theories about natural selection.

106
The phrase is often felt to be unhelpful - biologists almost
exclusively use ‘natural selection’ instead. The term
‘fitness’ is a subjective one, i.e. there is no way to
measure ‘fitness’.
If it is measured in terms of
survival, the phrase becomes
“survival of the survivors” which
doesn’t make sense.

107
In early Victorian times, the concept of survival of the
fittest was used to justify social inequality and the great
disparity between classes.
The 1850s and 1860s were the
decades when Charles Dickens was
writing and his novels describe the
social injustice that existed at the
time.
Charles Dickens 1812 - 1870

108
A weak point of Darwin’s theory was that
nobody knew exactly how different
characters came into being because
genetics hadn’t yet been developed as a
science..

109
Today we know that the main factors which bring about
variants are:
• Mutations
• Genetic Drift
• Gene flow
There are some other ways
(e.g. so-called gene hitchhiking)
that will be discussed as part
of genetics.

110
These are random changes in the DNA. A single
mutation can sometimes have a large effect, but
usually, evolution depends on the
accumulation of several mutations.
Left mutated whippet -
increase of muscle mass
and twice the size of
normal whippet (right)

111
Most mutations are harmful (even
lethal) or of no significance but
sometimes they give an organism
the edge when competing against
other individuals

112
Not all morphological
changes are due to
mutations; they may also
have environmental
causes.
Cold temperatures during the embryonic
stage caused this ‘doubling’ of the front
legs of this mite.

113
This is the random change of gene frequency between
one generation and the next, due to the random of gene
distribution uring reproduction.
The ratio of brown to green marbles “drifts” around (5:5, 6:4, 7:3, 4:6 . . .)

114
This is different from
classical natural selection
because it is random while
natural selection is
essentially non-random.

115
This is the transfer of genes from one population to
another through interbreeding. If it occurs between
species it is better known as gene transfer.

117
After Darwin, many scientists
contributed to understand
better the process of
evolution and, as new
information is acquired,
different facets begin to
emerge.

118
Microevolution
Changes in gene frequency in a
population that give rise to
relatively small modifications over
a short period of time.

119
Macroevolution
The descent of different species
from a common ancestor over
many generations.

120
Macroevolution
on the left-hand
panel shows the
development of
new species.

121
Microevolution on
the right shows
changes
undergone by a
single ancestral
species to give
rise to closely
related ones.

122
This occurs when two distinct
species with differing
ancestries evolve to display
similar physical features.
Dolphin (mammal), ichthyosaur (reptile),
swordfish (fish) and penguin (bird) all show a
similar shape (morphology) because they all live
in the sea.

124
This is said of an organ or structure that appears similar in
unrelated organisms.
All animals which fly
have wings which are
superficially similar,
even though the
animals themselves
are unrelated.

125
This occurs when two independent species evolve
together at the same time in the same eco-space and
acquire similar characters.

126
Non-related species acquire similar characteristics
through in similar ecosystems but at different times— e.g.
the dorsal fins of ichthyosaurs and sharks.
The ichthyosaur (top) is a reptile, the
shark (left) a fish but the two animals
are similar body shapes.

127
This is when related species evolve different traits. The
accumulation of such differences can eventually lead to
the formation of new species.
Creation of botanical
variants of Brassica
oleracea. In this case the
different types are not
species but varieties.

129
This is when the same organ or structure takes on a
different shape in different organisms. This is considered
one of the main pieces of evidence in favour of evolution.

130
The skeleton of the upper limb in different mammals shows the same
bones, though modified in shape.

131
This refers to changes in
which two opposing
characters are both
favoured over the others
and the population is
divided into two distinct
groups.

132
In this process, diversity
decreases as new
characters are not beneficial
and die out. The population
is thus stable and does not
undergo changes.

133
This happens when a
single set of characters is
favoured over all others so
that the population as a
whole undergoes change.

134
This is when two or
more species inluence
the evolution of each
other.
E.g. The evolution of a
parasite and its host or
that of flying insects
and flowering plants.

136
There is a very large amount of
information and scientific fact to
prove that evolution has and is still
occurring.
Moreover such evidence also
shows us how takes evolution
place.

137
All the evidence available may be grouped in these five
sections:
1. Evidence from palaeontology
2. Evidence from comparative anatomy
3. Evidence from comparative embryology
4. Evidence from geographical distribution
5. Evidence from comparative physiology and
biochemistry

138
sections:
biochemistry

139
The study of past life based on fossil records and their
relations to different geological time and layers provides
us with information on the evolutionary history of life on
Earth.
• Fossil records
• Development of
species
• Living fossils

140
Fossils show us what kind of organisms were alive
hundreds of thousands or millions of years ago.

141
The number and complexity of
different fossils at different rock
levels show that:
Older fossil-bearing rocks contain
fewer types of fossilized
organisms and they all have a
more simple structure.
Younger rocks contain a greater
variety of fossils with structures
which are increasingly complex.

142
Sedimentary rock is made up of a series of horizontal layers or
strata, each containing fossils typical for that time period when
they were laid down.
The lowest strata, i.e. the oldest
rocks, have the earliest fossils
while higher strata contain
younger rocks with more recent
fossils.

143
A succession of organisms can be seen from fossils which supports a
theory of progressive increase in complexity of these organisms.

144
Sedimentary rocks, such as
fossil-bearing limestone, can
also help geologists determine
geologic time. Because the
bottom layers were deposited
first, the oldest fossils are
found there.

145
The accumulation of shells or
other fossils in limestone provides
us with a record of the organisms
that used to live in the ancient
oceans.
Fossil from Gozo

146
One of the first fossils ever described in
scientific literature had been discovered
in Malta.
In 1670, Agostino Scilla illustrated three
teeth in a fossil whale jaw from Malta.
It represents the species
Squalodon melitensis, a
shark-like whale.

147
Scilla's illustration, (top,) shows three
molar teeth with triangular crowns with
many small projecting denticles. Each
tooth has two roots.
The fossil is still in existence in the
Sedgwick Museum at Cambridge
(bottom)

148
It is possible to find out how a particular group of organisms
evolved by arranging its fossil records in a geological
sequence.

149
Such a sequence can be worked out because fossils are
mainly found in sedimentary rock.

154
A particularly well-
documented case of
evolution within a group.

155
But, the standard diagram of the
previous slide does does not
clearly show transitional stages
whereby the four-toed foot of
Hyracotherium, otherwise
known as Eohippus, became
the single-toed foot of Equus.
Fossils show that the
transitional forms predicted by
evolution did indeed exist.

157
The teeth of extinct animals allow us to find out what
they were eating and how they lived.

158
sections:
biochemistry

159
Comparing the anatomy
of groups of organisms
reveals that certain
structural features are
basically similar.

160
The basic structure of all flowers consists of
the same parts but the size,
colour, number and shape of each
part are different for each individual
species

161
When widely separated groups of organisms
originate from a common ancestry, they
are expected to have
certain basic features in
common. The degree of
resemblance between
organisms should
indicate how closely
related they are in
evolution.

162
A giraffe (left) and goat (right)
both have cloven even-
numbered hooves, showing
they are related.
A rhino (left) and horse (right) both have
hooves with an odd number (3 and 1) showing
they are related.

163
Do the stripes on a tiger
and a zebra indicate that
the two animals are
related?

164
In comparative anatomy we have to consider the
following aspects:
• Homologous structures
• Analogous structures
• Vestigial organs

165
Forelimbs of mammals have the same bones but modified
for different uses. It would make no sense if the organisms
were specially created, but is logical if they share a
common ancestor.

167
Homologous structures having common origin. Even though the forelimbs
have evolved to carry out different tasks they are all constructed from the
same bones.

168
Under similar environmental conditions,
different structures in different groups of
organisms may undergo changes to serve
similar functions. This phenomenon is
called convergent evolution.

169
The dorsal fin of a
shark has a
different origin to
that of a dolphin.

170
Similar structures in organisms apparently
bearing no close phylogenetic links but showing
similar adaptions to perform similar functions are
described as analogous.

171
This happens when organisms which are not related but
which live in similar habitats eventually acquire similar
structures and morphology. It is the origin of analogous
structures

172
Organs that are smaller and simpler in structure than
corresponding
parts in the
ancestral species
are called vestigial
organs. They are
usually degenerated
or underdeveloped.

173
These can be explained by changes in the modes of life
or environment of the species. They are thought to have
been functional in the ancestral species but have now
become unnecessary and non-functional.
Vestigial limbs in whale (left)
and snake (right)

174
All organisms contain
some vestigial structures
that give clues to the
past.

175
Wisdom
teeth
Appendix
Tailbone

176
Whale embryo
Modern whale Fossil whale

177
Appendix
Nictating membrane in eye
Arrector pili muscle at base of hair follicles makes hair stand up.

178
sections:
biochemistry

179
Embryos of many vertebrates
are very similar during early
development, suggesting
common descent.

180
For example, adult vertebrates are diverse, yet their
embryos are quite similar at very early stages. Fishlike
structures still form in early embryos of reptiles, birds,
and mammals. In fish embryos, a two-chambered heart,
some veins, and parts of arteries develop and persist in
adult fishes. The same structures form early in human
embryos but do not persist as such in adults.

181
Comparative embryology shows how embryos start
off looking the same.
As they develop, their
similarities slowly
decrease until they
take the form of their
particular class.
Homologous structures in
adults develop from
homologous groups of cells
in embryos: they share
developmental pathways.

182
sections:
biochemistry

183
Biologists have discovered
many puzzling facts about
the presence of certain
species on various
continents and islands
(biogeography).

184
It is not only living animals; fossils are also distributed
geographically in ways that indicate that evolution has
taken place. The same kinds of fossils are found from
areas known to be adjacent to one another in the past
but which, through the process of continental drift, are
now in widely divergent geographic locations.

185
For example, fossils of the same types of ancient
amphibians, arthropods and ferns are found in South
America, Africa, India, Australia and Antarctica, which
can be dated to the Paleozoic Era, at which time these
regions were united as a single landmass called
Gondwana.

186
Sometimes the descendants of these organisms can be
identified and show unmistakable similarity to each
other, even though they now inhabit very different
regions and climates.

193
Map showing distribution of present members of the
camel family (in blue)
Solid black
lines
indicate
possible
migration
routes

194
Fossil records show that evolution of camels started in N. America,
from where they migrated to S. America and Asia and then Africa.

195
Once each population was isolated it evolved along different lines,
giving the modern camel in Asia and Africa and llama in South
America

196
sections:
biochemistry

197
In all organisms, genetic hereditary information is
passed from one geration to the next through a
very long complex molecule
called DNA.
Strands of DNA make up
structures called
chromosomes.

198
The DNA strand making up the chromosome is
subdivided into sections called genes which
determine the characters of
the organism.

199
Among the building blocks of DNA are smaller molecules
(amino-acids) known as bases . There are
only four bases and they are found in all
organisms, from bacteria to humans

200
Darwin predicted that humans and primates would be found
to be closely related. Today we can test this hypothesis:
humans and chimpanzees share 98% of the DNA.
The DNA of nonhuman primate species is remarkably similar
to those found in human DNA.

201
Apart from DNA, there are many other molecules which are
shared by different organisms. Sometimes these molecules
are identical and,
at other times, they are slightly
different.
Both similarities and differences
can be used to prove that
organisms share a common
ancestor.
A model of a protein molecule.

202
An example is the variance of the protein known as
Cytochrome c. This protein has undergone mutations and is
slightly different in different species. By looking at the
differences between variants of the same protein therefore, it
is possible to count how many mutations have occurred. (see
example on next slide)

203
The protein known as cytochrome c of humans and
monkeys is different only because of one single
mutation that is generally
accepted to have occurred
4 million years ago.

204
Besides visible organs which have become vestigial,
humans also possess genes which are no
longer functional but similar
genes are still active in other
animals. It is thought that such
non-functional genes are
‘vestiges’.

Emp 1003 Evolution

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