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Evolution
Lesson objectives
By the end of this lesson you should know
that
• Variation is the result of sexual
reproduction and mutations.
• Discuss two agents responsible for
increased mutation rates.
Variation
“Variation means that
there are differences
between the members of
a species”
• Only inherited (genetic)
variations are considered
here
• Acquired variations are
not passed onto the next
generation
• Genetic variation is
caused by sexual
reproduction and by
mutations
Mutations
“A mutation is a change
in the amount or structure
of DNA”
• Mutations happen
naturally when DNA fails
to replicate properly – this
rate of mutation is
normally very low
• In addition, DNA has
enzymes that repair the
vast majority of mutated
genes
• Mutations occur at
random locations on the
chromosome
• The change in DNA
normally means the
protein cannot be made
• This can mean there will
be serious problems if the
protein is important for
the cell
• Mutations in somatic cells
may be sometimes
serious – cancer
• Mutations in gametes are
very serious because the
mutation may be passed
onto the cells of the
offspring
Causes of mutations
•
Agents called
mutagens can increase
the natural rate of
mutations
• Mutagens that cause
cancer are called
carcinogens
• Mutagens include:
1. Ionising radiation such
as X-rays, gamma rays
and ultra-violet radiation
2. Chemicals such as
cigarette smoke,
caffeine and
formaldehyde
Types of mutations – 2 types
Gene mutations
• Gene mutations affect
only small sections of
DNA (i.e. affect only 1
gene)
• These mutations
cannot be seen but
their effects can
• Examples: albinism,
cystic fibrosis, sickle
cell anaemia
Types of mutations – 2 types
Chromosome mutations
• Chromosome mutations affect large areas
of a chromosome or can involve an entire
chromosome and sets of chromosomes
• Examples Down’s Syndrome (results
normally from the egg containing 24
chromosomes combining with a normal
gamete of 23 chromosomes)
What do you know?
Do you know that . . .
• Variation is the result of sexual
reproduction and mutations.
• Discuss two agents responsible for
increased mutation rates.
Lesson objectives
By the end of this lesson you should
know the:
• Definition of "evolution".
• Theory of Natural Selection. Evidence
from any one source.
Evolution
•
•
•
•
•
“Evolution is the way in
which living things change
genetically to produce new
species over long periods
of time”
Theory proposed by Charles
Darwin in 1858
Got many of his ideas when
he worked on board the HMS
Beagle
The ship sailed around the
Galapagos islands in the
1830’s
Alfred Russel Wallace has
come up with the same ideas
around the same time
Wallace stimulated Darwin to
publish their joint theory
Charles Darwin
• English naturalist
• Born 1809
• While studying
theology he became
interested in natural
history
• 1831 - invited to join
an expedition to map
coastline of South
America
HMS Beagle
The Voyage
The Voyage
In Brazil he saw his first tropical forest
The Voyage (Argentina)
• In Argentina he found
his first fossils –
sloths, mastodons,
and horses
The Voyage (Chile)
• In Chile, Darwin witnessed an earthquake
and observed both its effects in raising
the level of the land and its connection
with volcanic eruption. Repeatedly when
ashore he went on long, arduous, and
dangerous expeditions on horseback,
collecting and shooting, which showed that
his addiction to sport had not been
useless.
The Galapagos Islands
The Galapagos
Islands are located
650 miles west of
Ecuador in the Pacific
Ocean.
Species on the islands
• Dozens of unique species of both plants
and animals found nowhere else in the
world
• Giant tortoises
• A comorant that has lost its ability to fly
• The only lizard that feeds in the sea
• The only equatorial penguin in the world
Galapagos reptiles
Giant Tortoises
Harriet – she didn’t look a day
over 154
• Harriet was one of three
tortoises Darwin brought
back from the Galapagos
Islands to England
• Subsequently, he gave
Harriet to a friend
heading for Australia
• Harriet was mistakenly
considered a male for
over 100 years
• She died in June, 2006 at
an Australian Zoo where
she’s been a key
attraction for years
Galapagos birds
Galapagos birds
A unique form of giant cactus
Darwin’s visit to the Galapagos
• Darwin’s visit to the Galapagos for 5
weeks in 1835 provided the starting
point for his theory of natural selection
• He did not understand a great deal of what
he was seeing when he was there
• It wasn’t until he got back to England and
had ornithologist John Gould and other
experts look at the finches that he
realized he had discovered something big
The different types of finch
• The diversity of beak
structure and feeding
habits within the group of
finches is remarkable
• The different species are
adapted to feed in a
variety of ways
• Some eat seeds
• Some eat insects
• Some remove ticks from
tortoises
• Some eat leaves
• Some eat flowers
• Some drink blood from
seabirds
• Some use twigs to
extract insect larvae
Back Home
• At first his interests were geological e.g. he
discovered in the Andes – at an altitude of 7000
feet – a fossil forest overlain by thousands of
feet of sedimentary deposits laid down by the
sea, thus proving the occurrence of earlier earth
movements of the order of 10,000 feet vertical
height
• In 1856 Darwin started to put on paper his
discoveries about evolution and natural selection
Back Home
• In 1858 out of the blue, he received from Alfred
Wallace, a naturalist then in the Malay
Archipelago, a succinct but complete statement
of his own conclusions on evolution and natural
selection
• A joint paper by both was read to the Linnean
Society of London in 1858
• Darwin then made an abstract of the work on
which he had been engaged for 20 years
• This abstract was called the Origin of Species
which was published on November 24, 1859,
and sold out immediately
“Origin of Species”
• In the eyes of posterity, his publications on
geology were so eclipsed by the
bombshell on evolution that they have
been neglected
• With his book Darwin brought down on
himself enemies of two kinds. Scientists
(Adam Sedgwick and Richard Owen) and
upholders of orthodox religious beliefs e.g.
Samuel Wilberforce, bishop of Oxford
What was in the book?
• In it, Darwin makes one long argument
with copious examples as support, for his
theory that organisms gradually evolve not
individually but in groups through the
process of natural selection, a
mechanism the book effectively introduced
to the public.
Summary – statements 1 and 2
• S1 Organisms produce far more
offspring than ever give rise to adult
individuals
• S2 The numbers of individuals of a
species remain more or less the same (in
a particular ecosystem)
Deduction 1
• Therefore there must be a high death
rate, resulting from the constant struggle
taking place between all organisms for
food, in avoiding predators and disease,
and in coping with climatic conditions
Statement 3
• S3 The individuals in a species are not all
identical, but show variations in their
characteristics that have arisen, by
chance, through sexual reproduction and
mutations
Deduction 2
• In the competition for survival, variations
allow some individuals to adapt, survive
and reproduce better than others, so
passing on these ‘successful’ traits to
their offspring. Over many generations,
these small changes accumulate until two
groupings within the population can no
longer interbreed and a new species is
formed
Evolution
“Evolution is the changing of
one species into another
that takes place through
natural selection”
Evidence for evolution
•
•
•
•
Palaeontology: The study of fossils
Comparative Embryology
Comparative Anatomy
Comparative Biochemistry
Palaeontology
• Fossil Record ( Palaeontology)
• Fossil = Remains of an organism or evidence that it once
existed
Fossils
• Actual remains e.g. Bones and Teeth
• Rock Fossils e.g. Casts or impressions of organisms
and petrifaction of organisms
• Ice Fossils e.g. Woolly Mammoths in Siberia
• Amber Fossils e.g. flies trapped in resin which becomes
amber.
Palaeontology
• Sedimentary rocks are laid down in layers making it
possible to date the fossils in each layer. The
organisms in the lower layers being older than those
in the top layers. The changes which occurred over
time can clearly be seen in clear, simple and
sequential fossil records
Comparative embryology
• Embryos of different
species tend to pass
through the same stages
of development e.g.
Human embryos have gill
slits at an early stage
• The similarities in the
these stages of
development can reflect
the evolutionary
relationships between
organisms
• The genes for basic
embryo development e.g.
Hox genes are shared by
many complex animals
Comparative anatomy
Biochemistry
• If you compare the chemicals e.g. DNA,
Haemoglobin, ATP found in different
animals and plants, the degree of similarity
between these organisms can be
measured
• There is a 1% difference between our DNA
and that of Chimpanzees
Famous debate at Oxford 1860
• Thomas Huxley “Darwin’s bulldog” vs
Archbishop Samuel Wilberforce “Soapy Sam”
• Wilberforce was coached against Huxley by
Richard Owen , a biologist
• Wilberforce ridiculed evolution and asked Huxley
whether he was descended from an ape on
his grandmother’s side or his grandfather’s
• One account has it that Huxley concluded his
brilliant defence of Darwin’s theory, by saying “ I
would rather be the offspring of two apes
than be a man and afraid to face the truth”
Evolution
• Note: there is no direction or plan
to Evolution; it is merely the rule
book for the game of life.
• As Darwin concluded his book
“The Origin of Species by Natural
Selection “
• “There is a grandeur in this view
of life, with its several powers,
having been originally breathed by
the Creator in a few forms or into
one ; and that, whilst this planet
has gone cycling on according to
the fixed law of gravity, from so
simple a beginning endless forms
most beautiful and most wondrous
have been and are been evolved”
Other examples of Natural
Selection in action include:
• Evolution of pesticide resistance in
beetles, incidence of sickle cell anaemia in
areas which historically had malaria and
the evolution of antibiotic resistance in
bacteria.
How Evolution Works - Natural Selection
Both –
unpolluted area
Both – polluted area
Biston
Betularia,had
the
•• The
environment
Peppered
Moth
changed
and
now
for themoth
black
• selected
The peppered
form
of the
moth,
so by
comes
as two
forms,
a
1898
in one
the polluted
typical
which is areas
of
Englandcoloured
like
peppered
to
Manchester
black
camouflage the
itself
on the
form
made
up over
95%
lichen
covered
barks
of
of
the and
moths
population
trees
a mutant
black
and
peppered
form
formthe
which
was first
less
thanin5%
noticed
1848 in
Manchester
• This
process is known as
Selection
• Natural
Pollution
from the
Industrial Revolution in
England killed the lichens
on the trees and covered
their barks with soot
making them black
Religious problems
• The issues for religious believers were two fold
• If evolution was true, the account of the Creation
in the Book of Genesis was false or, at least not
literally true
• If evolution worked automatically by natural
selection, there was no room for divine
guidance and design in the production of living
plants and animals, including man on earth.
• Darwin’s findings became well known but
eventually gave Fitzroy great distress because
he was a creationist
Darwin’s Theory of
Evolution
o Many are born
o Not all survive
o Individuals vary
o Variations are inherited
o ‘Useful’ variations increase
What do you know?
Can you . . .
• Define "evolution".
• Discuss the theory of Natural Selection
and give evidence from any one source.