From genetics…to evolution

What is the Theory of evolution?

Darwin’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”

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 mis-copy) will generate complexity, diversity, beauty and an illusion of design so persuasive that it is almost impossible to distinguish from deliberate

intelligent design’

How similar are we?

• How different are we?

• Gene comparison slider

Charles Darwin…

An introduction to Charles Darwin….

Opponents to The Theory of Evolution: The Blind Watchmaker

oh yeah, it's David Attenborough again...

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

How are we different?

Discontinuous variationPhenotype has distinct categories

There are no ‘in- betweens’• Blood types• Genetic diseases• ‘Traits’: tongue rolling,

hitch-hikers thumb

How are we different?

Continuous variation

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

1. Meiosis

2. Random fertilisation

3. Mutation

Affects BOTH continuous AND

discontinuous variation

Environmental effects on genotype

Tends to affect continuous variation

alone

Environmental effects on phenotype

Sequoia sempervirens tree

Meiosis and genetic variation

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

• Definition: A change in a gene or a chromosome

• ‘COPYING ERRORS’ OF DNA• Mutations are the source of brand-new characteristics in the

gene pool• They are the final source of all genetic variation• Mutations can occur WITHIN a chromosome• Another type of mutation affects whole chromosomes (non-

disjunction)• How mutation works

Causes of mutation (2)

• Radiation• Chemicals• Viruses• Diet• Stress• Lifestyle• ?Gamma radiati

on?....

‘Hiroshima – the most

cynical Biology experiment of all

time’

Evolution in response to environmental change

1. Peppered moths in Great Britain

2. Antibiotic resistance in tuberculosis

3. Sickle Cell anaemia

1. Peppered Moths in the UK

Peppered moth simulation

2. Antibiotic resistance in bacteria

3. Sickle Cell anaemia

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’

Evidence for Evolution

• 1. The Fossil Record• 2. Artifical Selection – breeding of plants and

domestic animals• 3. Geographical Distribution• 4. Homologous Structures

Using our genome to understand human evolution

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 1: 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

http://www.pbs.org/wgbh/evolution/sex/mating/index.html

Evidence for Evolution 2: Homologous structures

• Homologous traits have similar embryological origins and development

• Indicative of common acnestry: 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

Evidence for evolution: Geographical Distribution

• Before humans arrived, Australia had > 100 types of marsupials, but no placental mammals

• Hawai’I and New Zealand had unique biotic environments – plants, insects, birds but no placental mammals

Evidence for Evolution: Observable Changes

• Development of new species is RAPID in species with a short reproductive cycle: bacteria, viruses, parasites, moths etc etc etc