Download Darwin`s Explanation: Natural Selection

Unit 10: Evolution
Ch. 29 Evolution
History of Earth
• Earth ~4.6 billion
years old
– early Earth
• hostile environment
– volcanoes, lightning,
meteorites, UV light
• primitive atmosphere
– methane, ammonia,
hydrogen, water
vapor
» What’s missing?
Origin of Life
• Life ~3.5 billion
years old
• Miller & Urey
– simulated primitive
atmosphere
• zapped w/ electricity
– ~1 week amino acids
& other simple
organic molecules
formed (in water)
» precursors to 1st cells
The First Organisms: Heterotrophs
• “Heterotroph Hypothesis” or “Primordial
Soup Hypothesis”
– Started w/ simple compounds  complex
compounds  primitive pre-cells 
prokaryotes (1st cells)
• 1st cells were heterotrophs
– Why heterotrophic?
» b/c no O2 for cellular respiration/photosynthesis
– fed on organic material (primordial soup in ocean)
» Similar to some present-day bacteria, obtained energy
from simple chemical reactions
Later Organisms: Autotrophs
• prokaryotic autotrophs followed heterotrophs
– What did they release into the atmosphere?
• oxygen (causing the oxygen revolution!)
– Why is this so important?
» allowed development of eukaryotes & complex organisms
stromatolites
What is Evolution?
• theory that species
have changed
gradually over time
– individual’s genes
stay the same
– population’s gene
pool (total genes) may
change
• evolves as allele
frequencies (%) (how
often an allele occurs)
change due to natural
selection
Mechanisms of Evolution
•
•
•
•
migration
genetic drift
mutation
natural selection
Mechanisms of Evolution
• migration
– gene frequencies
change as
individuals
move in or out
of the population
• genetic drift
– change in gene
pool of a small
population that
takes place strictly
by CHANCE
Mechanisms of Evolution
• mutation
– random change in the DNA sequence of a gene
• can change amino acid sequence & protein coded for
– can change the way the trait is expressed
• not all mutations matter in evolution
– must be heritable (in gametes)
Mechanisms of Evolution
• natural selection
– organisms with variation best suited
for environment tend to survive, &
reproduce (“survival of the fittest”)
• more offspring will have favorable
adaptation than before
– acts on individuals, but causes
evolution of population
•Which trait was a better
adaptation and selected?
•How were frequencies of
different alleles affected?
Explanations for How Evolution Happens
• Jean Baptist
Lamarck
– “Theory of
Acquired
Characteristics”
• acquired traits are
passed on
– leads to changes
in species
–experimentation
failed to support
Lamarckism
Explanations for How Evolution Happens
• Charles Darwin
– naturalist on HMS Beagle
• collected fossils & specimens
• observed tremendous biodiversity
Climate varied from island to island.
intermediate shell
domed
Shell
large rainfall
saddlebacked
shell
desert
Explanations for Evolution
– concluded, life forms can & do change….
• but, questioned how this change occurred…
–concluded  evolution or “descent with modification”
»still needed to test ideas before explaining how
or why such changes happen
Darwin’s Explanation: Natural Selection
– wrote On the Origin of Species by
Means of Natural Selection (1859)
– Darwin’s Main Points:
1. Overproduction of offspring
2. Struggle to survive
–
competition
3. Variation within population
4. Successful reproduction
–
“survival of the fittest”/best adapted
organisms are “naturally selected”
Video: Who Was Charles Darwin?
Darwin’s Explanation: Natural Selection
1. Overproduction of offspring
– Why is this necessary?
• to ensure that at least some will survive long enough
to reproduce & pass on genes
Video: Darwin & Malthus
Darwin’s Explanation: Natural Selection
2. Struggle to survive
– more organisms than
resources to go around
leads to competition
• For what?
– food, shelter, mates, space,
light, water, nutrients, etc.
• Survivors 
– Who are they?
– How did they get these
traits?
– Were these traits a response
to their environment?
Darwin’s Explanation: Natural Selection
3. variation w/in population
– What causes variety?
• Sexual reproduction
• Crossing over during meiosis
• Arrangement of chromosomes
during meiosis
• Mutations
– Darwin did NOT have
knowledge of genetics
Darwin’s Explanation: Natural Selection
• variations
– can be adaptations
– are NOT a response
to environment
• just happen to be
“useful” when
environment changes
camouflage
Darwin’s Explanation: Natural Selection
4. successful
reproduction
– natural selection
• Those organisms
best suited for
environment tend to
survive, reproduce,
& pass on genes
(“survival of fittest”)
– more offspring have
favorable adaptation
than before
Pepper Moth “Game” http://www.techapps.net/interactives/pepperMoths.swf
Principles of Natural Selection "Interactive"
How would Darwin adjust the description given
by Lamarck about the length of giraffes necks?
Lamarck vs. Darwin
Darwin’s Explanation:
Wallace’s Same Conclusion
• Alfred Wallace
(1858)
– arrived at same
basic explanation
as Darwin
• Darwin usually
given credit
– but BOTH men
should be credited
Evidence to support the
Theory of Evolution
• indirect evidence
– fossil record
– comparative anatomy
– comparative embryology
– comparative biochemistry
• direct evidence
– current observations
Indirect Evidence: Fossil Record
• Fossil Record
– Evidence of:
• change in
organisms over time
• age of the Earth
–
Limited b/c:
•
•
decomposition
type of material
–
•
incomplete record
–
•
What fossilizes
best?
Why?
easily disrupted
–
Why?
Which layer is
youngest?
oldest?
Explain…
Law of
Superposition
Indirect Evidence: Comparative Anatomy
• comparative anatomy
– compares structures of diff. organisms living today
1. homologous structures
2. analogous structures
3. vestigial structures
Indirect Evidence: Comparative Anatomy
1. homologous
structures
• similar
structure w/
modifications
− evidence of
common
ancestor
•
becoming
more
different
(divergent
evolution)
Indirect Evidence: Comparative Anatomy
• 2. analogous
structures
– similar function,
but not structure
• due to similar
environment/use
• do NOT have
common
ancestor
– becoming more
similar
(convergent
evolution)
Indirect Evidence: Comparative Anatomy
• 3. vestigial
structures
– structures with
reduced size
or function
• often no
apparent use
anymore
– evidence that
organism has
changed
Indirect Evidence: Comparative Embryology
• embryonic
development
– early stages  very
similar
• later stages  more
distinction
– inherited same basic
body plan from
common ancestor
• greater # similar
stages  more
closely related
Indirect Evidence:
Comparative Biochemistry
• similar organic
compounds coded
for by similar DNA
– ex. proteins
Indirect Evidence:
Comparative Biochemistry
• DNA  most reliable form of evidence
• What is the significance of 2 very different species
sharing large amounts of the same DNA?
– evidence of common ancestry
• higher %, more closely related
– human & chimpanzees 98% similar
– humans & other mammals 80% similar
Direct Evidence: Observation
• “rapid”
evolution
1. antibioticresistant
bacteria
2. pesticideresistant
insects