Lecture 2 Flashcards
George Cuvier 1726-1832
- Identified basic morphological plans
(bauplans) - Saw history as a series of creation
periods and extinctions through
natural catastrophe: catastrophism - No change: just extinction and
replacement
Jean Baptiste Lamarck 1744-1829
- Variation acquired over an organism’s
lifetime is passed on - Inherent tendency towards complexity
over time - Didn’t believe in extinction
Alfred Russell Wallace
(1823 – 1913)
- Independently developed a
very similar theory to Darwin’s - Corresponded with Darwin to
discuss their ideas - Had work published alongside
one another - This prompted Charles Darwin
to publish his book - Arguably had a greater impact
on evolutionary theory e.g.
‘the father of biogeography’
William ‘strata’ Smith (1769-1839):
- Observed rock layers, ‘strata’ at a mine pit
- Arranged predictably: always in same relative positions
- Each stratum identifiable by the distinctive fossils it
contained - Same succession could be found in many parts of the
UK: older to younger rocks?
Charles Lyell (1797-1875)
- Popularised “uniformitarianism” (the theory that changes in the earth’s crust during geological history have resulted from the action of continuous and uniform processes)
- Geological [and presumably other!] processes seen today are the
same as those seen in the past, i.e. are uniform over time - Slow moving: i.e. vast time depths were needed
Wednesday 27 April 1859
Sir John Evans and Sir Joseph Prestwich (with several other
respected scientists) present at the in situ find of a handaxe at
St Acheul in France
* First use of photography for a scientific purpose
* Caused controversy!
* Sir Charles Lyell went to visit, was convinced, and promoted the
theory back in the UK
* Followed almost immediately by the publication of The Origin of Species
Charles Darwin
(1809 – 1882)
- Ship’s naturalist on HMS Beagle
- Voyage to the Galapagos Islands
1831 – 1836 - Noticed patterns of geography and
variation among animals - Origin of Species 1859
- Influenced by Thomas Malthus’
ideas on population growth at
geometric rates if unchecked - Combined with his observations of
variation in morphology and
behaviour
Darwinian Theory: the basics
- Individual organisms within a population
vary in their traits. - This influences their ability to access finite
natural resources and hence their survival
and reproductive success. - Individuals with traits that enhance chance
of survival and reproduction contribute
disproportionately to the next generation. - The variation is inherited by offspring.
- There is a shift in the frequency of traits in
the population. - If the process continues for long enough,
eventually the group can no longer breed
with others… - … and constitute a separate species.
Genotype
an individual’s genetic code
Phenotype
observable physiological traits
Variation arises through
- Recombination, e.g. combining 2x parents’ DNA in each child
- and mutations, i.e. mistakes in the copying procedure
Not all mutations are heritable
Somatic mutations occur in body cells and are not heritable
Germline mutations in gametes (egg or sperm) are heritable
Not all mutations affect phenotype and those that do may vary in their effects
- ‘silent’ mutations or mutations in non-coding DNA etc.: do not affect amino acid sequence
- ‘missense’ mutation: slightly different amino acid sequence
- Nonsense mutation: amino acid sequence production stops
- Frameshifts: major difference in amino acid sequences because they move large sequences forward or back along
the gene
Natural selection and differential
reproduction
- Individuals compete for limited
resources - Different phenotypic
characteristics result in consistent
differences in rates of survival or
reproduction (on average) - BUT the differences in phenotype
must be at least partly to do with
genotypic variation - i.e. acquired phenotypic differences
are not passed on!
Ecosystems and community
ecology
The other species in your biome
are agents of natural selection
Competition: results in
*Extinction for one species OR
* Reduction of competition BY
1. Temporal e.g. seasonal/diurnal
2. Structure e.g. vegetation levels
3. Spatial separation into microhabitats
Co-evolution
- Traits in one species have evolved in
response to traits of another species
e.g. predator-prey relationships - Red Queen hypothesis
- mutualism/parasitis
Adaptation
any structure, physiological
process or behavioural pattern that
makes an organism more fit to survive
and reproduce
* Not all traits are adaptations!
* There is no such thing as a ‘transitional
form’ (only with hindsight!)
* All adaptations must improve things
(however marginally) for the individual
possessing it in the evolutionary present
* Adaptations can be behavioural as well
as physiological!
Exaptation
- Exaptus = Fit by reason of
- A trait evolved for one purpose
becomes co-opted for another - e.g. feathers: evolved for warmth or
flight?
Vestigial traits
- Traits which are no longer useful
(or are they?!) - E.g. whale hip bones; human
appendix
Mutation and natural selection:
frequency changes
in traits
- Mutation produces variation
- Unfavourable mutations are
selected against and go
extinct - Reproduction, mutation and
selection continue - Favourable mutations are
more likely to survive and
reproduce - Favourable mutations spread
throughout the population:
evolution has occurred!
Directional selection
FOR: one extreme trait
AGAINST: the other extreme
e.g. long wiggly tails look like snakes to scare off predators.
Stabilizing selection
FOR: moderate traits
AGAINST: both extremes
e.g. short tails mess up a cats balance and long tails drag on the ground. Medium tails are best.
Disruptive selection
FOR: both extremes
AGAINST: moderate traits
e.g. short tails stop predators from catching you and long tails are good for balance. medium tails don’t help.
Sexual selection
Choosy females
* Male competition
* Runaway sexual selection:
linkage disequilibrium
* Can lead to ‘spandrels’
* E.g. peacock’s tail; human
brains?!
Assortative mating
- Positive (IQ; height)
- Negative (red hair; albinism?)
‘Artificial’ selection
- i.e. deliberate selective
breeding by humans
Genetic drift
- Gene frequencies can
fluctuate by chance - Usually in small, isolated
populations
Founder effect/genetic
bottleneck
- Small percentage of
population carries
reduced proportion of
genetic diversity
Anagenesis
species A
becomes species B
Cladogenesis
species A
becomes species C and D
Allopatric populations
*separated by
physical/environmental barriers
* These physical barriers may change
over time
* Climate change
* Landscape change
Allopatric populations
*separated by
physical/environmental barriers
* These physical barriers may change
over time
* Climate change
* Landscape change
