From genetics…to evolution…’endless
forms most beautiful…’
Darwin (and Wallace) ’s Theory of
Evolution
• "the single best idea anybody
ever had” (Daniel Dennet, Philosopher)
• “a big idea, arguably the most
powerful idea ever “ (Richard Dawkins,
Philosopher)
• “Its
publication (The Origin if
Species) changed the world”
Some reminders (from genetics…)
How do we express difference?
Continuous/discontinuous variation
Discontinuous variation
Single gene traits
Phenotype has distinct
categories
There are no ‘in- betweens’
• Blood types
• Genetic diseases
How are we different?
Continuous variation
Due to contribution
from multiple genes
The variation in phenotype
follows a ‘normal-type’
distribution, with most
individuals falling in the
‘middle of the range’
Skin colour is another example of
continuous variation
What makes us different?
Genetic variation
Environmental effects on genotype
Environmental effects on
phenotype
Sequoia sempervirens tree
Meiosis and genetic variation
Genes are changed by
mutation
• The basis of
genetics
• ‘ the fuel for
evolution’
• ‘the destroyer
and creator of
life’
• ‘Thanks to
mutation, we’re
not all still in the
primordial soup’
Gene mutation
• A change in a gene or a chromosome
• Caused by ‘COPYING ERRORS’ OF DNA or ‘external’
damage to DNA
• Mutations are the source of brand-new
characteristics in the gene pool
• They are the final source of all genetic variation
• How mutation works
What is the Theory of evolution?
Evolution
Synonyms:
• Charles Darwin used ‘Descent with modification’
• ‘Survival of the fittest’
• ‘Theory of Natural selection’
Richard Dawkins’ Theory of
Evolution
‘Given sufficient time, the non –random survival of
hereditary entities (which will occasionally miscopy) will generate complexity, diversity, beauty
and an illusion of design so persuasive that it is
almost impossible to distinguish from deliberate
intelligent design’
• Gene comparison slider
Charles Darwin…
An introduction to Charles Darwin….
The Mechanism of Evolution:
Natural Selection
How does natural selection work?
1. Too many offspring (‘over-production’)
2. Genetic variation (sex and mutation)
3. Competition: the Struggle for survival
4. Differential survival and reproduction
(‘survival of the genetically fittest’)
5. Advantageous characteristics passed on
to offspring
6. GRADUAL change over many generations
Too many offspring
Results in competition for available resources –
food, shelter, mates, water, sunlight
Darwin’s Theory of Evolution by
Natural Selection can be
summarized with the simple
acronym VISTA:
Variation
Inheritance
Selection
Time
Adaptation)
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Natural selection takes several
forms
• ‘Stabilising’ selection in a stable environment
• ‘Directional’ selection in a gradually changing
environment
• ‘Disruptive’ selection in a fluctuating
environment
Natural selection does not always
cause change
• Change will only occur when there is
environmental change, or when a brand new
‘advantageous’ mutation arises
• Most of the time, natural selection keeps
populations stable over the generations: and
is considered as ‘stabilising selection’
• Extreme variations are eliminated and the
established phenotype is maintained
Directional selection
• Results in evolution of a population
• Associated with gradually changing conditions
• The phenotype gradually shifts towards the
‘better adapted’ variety
1. Peppered Moths in the UK
Peppered moth simulation
2. Antibiotic resistance in bacteria
Disruptive selection
• Favours two extremes of a trait at the expense
of the intermediate form
• Associated with a fluctuating environment
• Gives ‘balanced polymorphism’ (a balance of
different types)
Disruptive (diversifying) selection
Heterozygous advantage in natural
selection: Sickle Cell anaemia
Natural selection can lead to
speciation…
Natural selection can lead to
extinction…
You need to be familiar with the
evidence for evolution
Evidence for Evolution
1. The GENOME
2. The Fossil Record
3. Geographical Distribution
4. Artificial Selection – breeding of plants
and domestic animals
5. Homologous Structures
6. Embryological development
7. Adaptive radiation
Opponents to The Theory of
Evolution: The Blind Watchmaker
oh yeah, it's David Attenborough again...
Evidence for Evolution 1: DNA
By sequencing and databasing
genes, we can see similarities and
differences between species
• The closer the genome match, the
closer their evolutionary history
• Human Chromosome 2 came from
fusion of two great ape
chromosomes
• Karl Miller on human evolution
• The time-tree of evolution
Evidence for Evolution 2: The
Fossil Record
The Fossil Record
• Palaeontologists uncover
fossilised remains in
sedimentary rock deposits
and use the information to
create timelines
• Organic matter trapped in
sand/ silt/fossils
• Compressed over time
• Dated by isotopic carbon
(50,000 years),
potassium40 (1.28 Billion
years), 238 Uranium
• Oldest fossils are at the
bottom, youngest at the
top
Other methods for dating fossils
• Dating Methods
Fossil Evidence for Evolution
whale valley
Whale evolution
Evidence for evolution:
Geographical Distribution
• Before humans arrived, Australia had > 100 types of
marsupials, but no placental mammals
• Hawai’I and New Zealand have unique biotic
environments – plants, insects, birds but no placental
mammals
Adaptive radiation
The diversificaiton
(speciation) of a group
of organisms into
different types
specialised for different
ecological niches
Darwin’s finches….
Evidence for Evolution 2:
Homologous structures
• Homologous traits have
similar embryological
origins and development
• Indicative of common
ancestry: what Darwin
called ‘Unity of Type’
• Indicative of adaptive
radiation
• Pentadactyl limb
• Human appendix
• Whale pelvic and thigh
bone
Homologous structures:
Pentadactyl Limb
Homologous structures: Whale
Pelvic bone
Homologous structures: Human
appendix
Evidence for evolution 3: Artificial
Selection
Evidence for evolution: Artificial
selection
Artificial Selection
An avid pigeon breeder, Darwin knew that breeders
could change a species by choosing individuals with
interesting traits that occurred at random and by
allowing those individuals to breed. Over
generations, those traits become more common and
the population changes over time.
5
3
Darwin’s Observations
In addition to traits intentionally chosen by
breeders, Darwin noted this observation in The
Origin of Species
“. . . not a single domestic animal can be named
which has not in some country developed
drooping ears.”
54
Traits Common In Domesticated Species
Not only drooping ears, but also:
• piebald coloration, forehead star
• wavy hair
• rolled, shorter tails
• changes in reproductive cycles
What could this mean?
55
Wolves, Dogs, & Domestication
Dogs, the first domesticated animal species, were
domesticated from gray wolves in Southwest Asia
over 15,000 years ago.
Canis lupus
Canis lupus familiaris
56
Wolves, Dogs, & Domestication
• Morphologically, dogs and
wolves share a number of
traits because they are
canids.
• Genetically, they are 99.8%
similar in their mtDNA,
which strongly indicated
dogs were domesticated
from wolves. Wolves and
coyotes are only 96%
similar.
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Evidence for evolution: Embryology
Evidence for Evolution: Observable
changes in response to
environmental changes
Development of new species is RAPID in
species with a short reproductive cycle: bacteria,
viruses, parasites, moths…
Evolution in response to
environmental change
1. Peppered moths in Great Britain
2. Antibiotic resistance in
tuberculosis
3. Sickle Cell anaemia