These alternatives include the supernatural.

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Transcript These alternatives include the supernatural.

4 straightforward observations
150 years ago
Fossil records show that life used to be
2. Organisms are good at what they do
3. Organisms multiply in number
4. Children tend to resemble their parents
1. Evolution occurred
• We see in fossil record that evolution has
• How?
2. Organisms are good at what they do
Strong, curved beak of bald eagle can tear
flesh of large prey
Curlew uses low, curved, pointed beak to
get small crustaceans from the surface
of mud, sand and soil
Roseate spoonbill moves its bill through
water to filter food out
2. Adaptation
• = to become “apt” or to fit the
environment well
• Organisms are very good at what they
• How did this come about?
3. What if every couple has 4
Food supply can’t keep up indefinitely
Natural selection
• They can’t all survive
• Variation between individuals:
some are more likely to survive than others.
• Some variation is heritable,
since children tend to resemble their parents
• Next generation resembles
those who did best in previous generation
• Given time, lots of small changes
add up to make large changes
Artificial selection
We breed dogs,
pigeons and crops
for things we like.
Time scale of evolution
• Changes can be small and observed in
human lifespan
• Changes can involve whole new body plans
and take millions of years
• Key insight: same process
behind both
Like time scale of geology
• Changes can be small and
observed in human
lifespan: sand washing
down river
• Changes can be large:
forming a canyon
• Key insight: same process
behind both
Key components of evolution
• Variation within populations
• Selection on this variation (limited resources)
• Inheritance of this variation
Role of chance in evolution
• Variation appears by
• Selection is the
opposite of chance
What evolves?
• Genes mutate
• Individuals are selected
• Populations evolve
Teaching evolution
Evolution = variation + selection + inheritance
leading to change in a population
over time
Teach the components separately
1. Variation
2. Selection
3. Inheritance
4. Change in a population
5. Time
“Nothing in biology makes sense except
in the light of evolution”
Dobzhansky 1973
Teach everything in the light of components
Dissect a frog: variation between frogs
Desert adaptation: selection against those w/o it
DNA: inheritance of traits
Geology: time
Disease: antibiotic resistance is a change in a
General: appreciate the diversity of life matching
diversity of environments
What NOT to teach
• Living things are NOT perfectly designed
machines, every part of which serves a purpose
• Apparent design is real, and before Darwin, a
Creator was the best explanation we had
• The match between organisms and their
environment is called adaptation, and is the
problem that Darwin originally studied
• Now we have two explanations for adaptation:
design and evolution
Theory of evolution explains
other stuff too
• Evolution can’t design from scratch: it can only modify
what went before
• Sometimes this leads to “bad design”
• When we swallow, we risk
choking because our
breathing hole is in the
way, and needs to be
closed off.
• We inherited this bad
design from an ancestral
Another example of bad design
• Human nerve cells and retina are the other way around
• This leads to a blind spot, detached retinas, and light
distortion by nerves before it hits the retina
Nesse and Williams, Sci. Am. 1998
Progress and perfection
• Adaptation often looks so “perfect”: does
evolution somehow know where it is going?
• No! Natural selection has no foresight
• Only differential survival and reproduction.
• No perfection
• Only improvement on what went before for
a particular environment
• Lots of mess, waste and confusion in real
biology: it really isn’t perfect
Alternatives to evolution
Book of Genesis as the literal
2. Acceptance of evolution for
small changes, but not for large
3. Acceptance of evolution for
some things, but drawing the
line at human origin
4. Accepting all of evolution, but
that there is an additional
guiding force
Are the alternatives science?
Science takes the simplest theory to fit the data.
These alternatives place preconditions.
Science looks only at natural explanations.
These alternatives include the supernatural.
For better or worse, they are not science.
They could still be right.
Science and religion
ask different
Science asks what happened and how.
Religion asks for what purpose,
and what we should do about it.
Science looks for literal truths about the physical
Religion looks for profound truths that transcend
the physical world.
Purpose of life
Evolution has been criticized for depicting a world
with no purpose.
Purpose is a question completely outside of
science, neither confirmed nor denied by it.
Science and evolution are not atheistic:
they have nothing to say about religion one way
or the other.
Theological problems with creationism
• If the Earth really was 6000 years old and
evidence is there to trick us, then God is
deceitful: many would consider this blasphemy
• The vastness of life and the universe leads to a
larger understanding of God and a smaller role for
humanity. Rejecting this is presumptuous egotism.
God is what He is, not what we want Him to be.
• The Bible is written in a language that could be
understood at the time. Literalism is a narrow view
of a small God.
• Evolution may be God’s method of creation.
Aren’t there holes and problems in
evolutionary theory?
Science never explains everything.
Evolutionary biology gives a way of
going about explaining things.
In science, the more we do research, the more we
If we put God into all the gaps, then the more we do
research and fill the gaps, the smaller God gets
Irreducible complexity
Intelligent design’s alleged
scientific centerpiece.
Can multiple components
come together
simultaneously, with no
selection until all of
them are in place?
e.g. a mousetrap needs a
base, a bar, a spring
and a catch.
This combination is too
unlikely to come
together by chance.
Darwin already
considered this
Darwin went on to discuss intermediate
eye forms found in nature
– light sensitive cells
– depression that gives an indication of
direction without being so precise as a lens
Answer to irreducible complexity
Intermediate stages were, in fact, selected for.
Sometimes they kept the same function during
evolution, sometimes things were co-opted for
a new function.
Sometimes we have good evidence for the
intermediate stages, sometimes no living
animals or fossils have them any more.
Some types of evidence for evolution
1. Fossil record
2. Can find a consistent history or “family tree” of how
organisms are related to one another, using both
appearance and DNA
3. Biogeography: these trees correspond with what we
know about how continents move
4. Some evolution is fast enough to be directly
observed eg antibiotic resistance
This huge variety of observations (including geological)
make sense in the light of evolution, and lead to more
experiments. They would otherwise seem random.
Is evolution a theory or a fact?
eg gravity
the same
depending on the
Fact the
of being
mass of two objects, explains both falling to the
ground and planets revolving around the sun
Law things
a tendency
to the
to happen in a certain way
ground with a certain
Fact: anaapple
or hypothesis
to the ground
e.g. “I have a theory about this”
Summary: what evolution is NOT
NOT a completely random process
NOT change in an individual over time
NOT an inevitable form of “progress”
NOT proof that there is no purpose or
meaning to life
NOT proof that God does not exist
NOT justification for immorality (“is” does
not imply “ought”)
Summary: what evolution is
Variation, selection and inheritance
Change in a population over time
An explanation for the appearance of design in
living things (adaptation)
An explanation for examples of “bad” design
The intellectual framework for all of biology