Paul Overton - Lecture 1 - Natural Selection

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What is Paul Overton Lecture 1 about?
Natural Selection
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What was 'Darwin's finches' detailed in?
'The voyage of the Beagle'
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What were Darwin's finches?
13 species of small, sparrow-like birds living on Galapagos islands (off South America).
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Each species of Darwin's finches had...
A different beak suited to a particular feeding 'niche'.
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Finches played a....
Critical role in Darwin's thinking about how species arise
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Quote from Darwin 1859 - 'On the origin of species'
"Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that...one species had been taken and modified for different ends"
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Darwin proposed species originate....
Via process which he referred to as 'natural selection'
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1st stage of natural selection
Variation exists between members of same species
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2nd stage of natural selection
Some variation is heritable
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3rd stage of natural selection
Species produce more offspring than can possibly survive
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4th stage of natural selection
Individuals more suited to physical and biological environment in which they find themselves more likely to survive and so pass on those attributes to offspring
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5th stage of natural selection
Leads to changes within a species
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6th stage of natural selection
May get several pockets of change with different adaptations
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7th stage of natural selection
Eventually, diversification may be so great that new species are born
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Darwin pre-dated modern genetics; process can be re-cast in 'genetic terms' - 1
All organisms have genes - (code for proteins which regulate development of nervous system, muscles etc.)
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process can be re-cast in 'genetic terms' - 2
Genes are passed on from one generation to the next
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process can be re-cast in 'genetic terms' - 3
Many genes present in 2 or more alternative forms - 'alleles' (produce slightly different forms of same protein)
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process can be re-cast in 'genetic terms' - 4
Different alleles cause differences in development; will make individuals who are more/less suited to environmental context
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process can be re-cast in 'genetic terms' - 5
Any allele that can make more surviving copies of itself will replace alternative forms
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Natural selection =
Differential survival of alternative alleles
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Darwin focused on evolution of....
physical characteristics
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However, genes can also influence...
behaviour
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How do we know that genes can also influence behaviour because of which area of research?
Much work on fruit fly - Drosophila
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Gene-Behaviour relationship studied by: (1)
Use of mutagens (radiation/chemicals) to induce mutations. Some have behavioural differences
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Gene-Behaviour relationship studied by: (2)
Studying natural variation in population - e.g. activity pattern
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Most adult Drosophila have....
Activity cycle which repeats every 24 hour.
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Most adult Drosophila have activity cycle which repeats every 24 hour. However....
Some move around at random intervals (no cyclic pattern); some follow a shorter (19 hr) cycle; some follow a longer (29 hr) cycle.
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Why are there some differences in Drosophila's activity cycles?
Differences arise from differences in a single gene (termed the 'period' gene)
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What about higher species?
Migratory behaviour in warblers has a genetic component.
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Where do most Warblers spend summer?
Europe
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Where do most Warblers spend winter?
Africa
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If Warblers are prevented from migrating, most show....
'restlessness' at corresponding time.
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By selective breeding from migratory (M) and non-migratory (nM) warblers, can produce....
pure M and nM strains (i.e. strains which give rise to only M or nM offspring)
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Levels of selection - At what level does natural selection work? What is the 'unit of selection'?
Darwin - evolution = struggle between individuals to out-compete others in population; referred to as: Individual Selection. Claims natural selection acts at level of individual (or even gene? - Dawkins)
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Individual selection can be contrasted with...
Group selection (GS). Unit of selection = group (or even species). Animals behave for good of group. 'Lions rarely fight to the death because, if they did so, this would endanger the survival of the species'.
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Group selection idea basic to writing of early ethologists:
Tinbergen ('The Study of instinct'); Von Frisch ('The dancing bees'); Lorenz ('On aggression')
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Main proponent - Wynne- Edwards:
1962 - 'Animal dispersion in relation to group behaviour'. 1986 - 'Evolution through group selection'
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Wynne-Edwards invoked to explain: (1)
Threat displays (vs dangerous fighting) - e.g. rather than fighting, rival red deer confront each other at a distance and roar
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Wynne-Edwards invoked to explain: (2)
Population control. Birds often lay less eggs than they can successfully incubate. Why? GS: fecundity adjusted so that species does not over-exploit available resources
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Wynne-Edwards invoked to explain: (3)
Dominance hierarchies. Dominant and submissive individuals = common feature of social organisation of animals. Submission often has negative consequences for reproductive success
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E.g. elephant seals...Why 'accept' submissive status?
GS: population control
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What's wrong with group selection?
1. Many traits evolve which are not to group's advantage e.g. infanticide by male lions. When new male takes over pride, sometimes kill cubs already present. 2. Cheats will always prosper. 3. Groups do not go extinct fast enough
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What's wrong with Individual Selection?
Why do birds lay less eggs than they can incubate, or individuals accept submissive status? If populations are composed of 'selfish' individuals, how has cooperation evolved? Why are parents nice to their offspring?
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Natural selection -
Heritable variation between individuals leads to differential survival
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Natural selection = (in genetic terms)
Differential survival of alternative alleles. Both physical and behaviour are selected (focus=behaviour)
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At what level does natural selection work? Group
Animals behave for good of group
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At what level does natural selection work? Individual
Animals behave for good of themselves
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Card 5

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