Download Lecture 2 File

26/09/2016
In this lecture:
Darwin’s Ideas
A reminder
• Evolution is not just natural selection.
• Sexual selection and genetic drift are major
players in natural populations, and artificial
selection in domesticated ones.
Darwin
• The Origin was really only a precis (even at
400 pages!).
• This was a short version to prempt Wallace,
but why did he take decades to accumulate
evidence?
• Take 2 minutes to think.
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Darwin’s evidence for natural selection
Support from genetics
The modern synthesis
In the future?
Natural selection
• This leads to adaptive change. The
environment, predators, diseases etc. will
affect a population and lead to differential
survival / reproduction and so also change.
• Situations change! What works now may not
work later. Evolution can’t predict the future.
• It doesn’t want or need things, selection acts.
Why the wait?
• Expected resistance from
the church as a
challenge to the creation
story.
• Resistance from other
scientists.
• Resistance from his wife.
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Darwin’s Evidence
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Fossil Record
• Fossils do not appear
in a random order.
Simple forms are
older, more complex
animals are more
recent.
1. The Fossil Record
2. Comparative Anatomy
3. Embryology
4. Vestigial Structures
5. Domestication (artificial selection)
Comparative anatomy
• Organisms share
major features
suggesting they are
related.
• This is true even
when they have
different functions.
Analogy example
Homology vs Analogy
• Analogy (same function, different structure)
• Homology (same structure, may be different
function)
• Can you suggest examples?
• Take 2 minutes.
Homology example
• Implies convergence
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Embryology
Vestigial structures
• Remnants of
structures no
longer in use.
• Evidence of
ancestry and
change over
time.
• Embryonic retention of ancestral characters (e.g.
gills, tail).
Variation under Domestication
Artificial Selection
• With no direct observations of natural
selection available Darwin turned to domestic
animals.
• Much of the book is devoted to discussions of
artificial selection (dogs, horses, chickens and
especially pigeons).
• Why?
• This is superb evidence for natural selection as
it shows:
variation was naturally occurring
characters were inherited
selection could favour certain traits
• Therefore this could be applied to living
systems where the selection was natural.
Domestication
• Some ‘extreme’ traits
could be produced in
a few generations
from normal pigeons.
• This was true of many
different lineages and
would be familiar to
much of the audience.
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Problems
Brassica oleracea
• Darwin’s arguments were based on much logic
and interpretation rather than hard evidence.
• He was working at a time when there was little
hard natural science.
• We had few fossils, limited knowledge of species
from outside Europe and no understanding of
inheritance.
• Darwin was aware of the limitations of the data
and theory and even devoted a chapter to them.
Critics
• Darwin faced major
critics at the time.
• This culminated in a
debate at Oxford that
was largely a draw.
• Many scientists
however strongly
supported Darwin’s
case.
Since Darwin
• Huge amount of evidence have been added to
corroborate his fundamental ideas, but also
extend them greatly.
• Additional data from: inheritance, fossils,
development, direct observations.
• This culminated in the ‘modern synthesis’ with
the integration of genetics.
• Moving from the ‘fact’ (evolution happens) to
the ‘mechanism’ (how and why).
And where are we now ?
Gregor Mendel (1822-1884)
• Austrian
monk.
• Worked out
the basic
laws of
inheritance.
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Watson & Crick
R.A. Fisher (1890-1962)
"It has not
escaped our
notice that the
specific pairing
we have
postulated
immediately
suggests a
possible copying
mechanism for
the genetic
material."
J.B.S. Haldane (1892-1964)
• With Fisher and
Wright, one of the
founders of
population genetics.
• “The Causes of
Evolution” (1932): first
major contribution to
what became the
modern evolutionary
synthesis.
Ernst Mayr (1904-2005)
• Worked on methods
of speciation.
• Gave the ‘biological
species concept’
definition of
species.
• Invented Analysis
of Variance and
other statistical
tools.
• Theory of
population
genetics.
Theodosius Dobzhansky (1900-1975)
• “Nothing in Biology
makes sense except
in the light of
evolution”.
• Genetics and the
Origin of Species,
published in 1937.
William D. Hamilton (1936 - 2000)
• Explained how sex ratios
can deviate.
• Explained how natural
selection acts on social
behaviour (“kin
selection”).
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Summary
John Maynard-Smith (1920-2004)
• Most widely known for:
• applying game theory to
evolutionary biology
• the two-fold cost of sex
1. finding a mate
2. only ♀ have babies
What next?
• EVOLUTION - “descent with modification”
• Integrates data from:
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Fossil record
Dating methods
Molecular evolution
Molecular clocks
Population genetics
• Environmental drivers
climate
continental drift
extinctions...
Conclusions
• Epigenetics
• Cultural transmission
• Niche construction
“Extended
Evolutionary
Synthesis” ?
• Evodevo
• Comparative genomics
• Systems Biology
“Postmodern
Synthesis” ?
• Darwin initially had limited evidence for his
theory but huge leaps in the last century have
integrated major areas of biology to support
it.
• Involves genetics, behaviour (especially social
structures), embryology, and issues of
relatedness.
• Natural selection is extremely well supported.
Further Reading
• http://erwan.lageat.free.fr/R1/Articles/Article
s%20nature/Crick%20and%20Watson%20195
3.doc
• http://users.ox.ac.uk/~jrlucas/legend.html
• http://www.ncbi.nlm.nih.gov/books/NBK1012
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