Download Darwin`s Explanation: Natural Selection

Unit 10: Evolution
Ch. 12 Evolution
& Ch. 13 Adaptation & Speciation
300
History of Earth
• How old is Earth?
– ~4.6 billion years old
• What was early Earth like?
– hostile... a lot of volcanic activity & lightning,
many meteorite impacts, high levels of UV light
• What gases were in the primitive atmosphere?
– methane, ammonia, hydrogen, water vapor
• What gas was missing?
– oxygen
Origin of Life
• When did life 1st appear?
– ~3.5 billion years ago
• What did Miller & Urey
do in their experiment?
– simulated primitive
atmosphere & zapped it
with electricity
• What happened?
– ~1 week amino acids &
other simple organic
molecules formed (in water)
» precursors to 1st cells
The First Organisms: Heterotrophs
• What does the “Heterotroph Hypothesis” or
“Primordial Soup Hypothesis” state?
– simple compounds formed 1st  complex
compounds  primitive pre-cells  prokaryotes
(1st cells were heterotrophs)
• Why heterotrophic?
– b/c no O2 for cellular respiration
• What did they feed on?
– naturally organic material (primordial soup) in ocean (ex.
amino acids)
» Similar to some present-day bacteria, they obtained energy from
simple chemical reactions.
Later Organisms: Autotrophs
• What type of organisms followed the
prokaryotic heterotrophs?
– prokaryotic autotrophs
stromatolites
• What did they release into the atmosphere?
– oxygen (….causing the oxygen revolution!)
• Why was oxygen so important?
– allowed development of eukaryotes & complex organisms
What is Evolution?
• theory that species/populations
change over time
– Can an individual’s genes
change?
• No…
– Can a population’s gene
pool (total genes) change?
• Yes…
– when allele frequencies (%)
change due to natural selection
4 Mechanisms (Causes) of Evolution
• 1.How does
migration cause
evolution?
– gene frequencies
change as individuals
move in or out of the
population
• 2. How does genetic
drift cause evolution?
– pure CHANCE
causes a change in
gene pool of a small
population
4 Mechanisms of Evolution
• 3. How does mutation cause evolution?
– random changes in DNA sequence can change
amino acid sequence & protein coded for… &
can change how the trait is expressed
• Do all mutations matter in evolution?
– No… to matter they must be in gametes
» …able to be passed down (heritable)
4 Mechanisms of Evolution
• 4. How does natural
selection cause evolution?
– organisms with the variation
best suited for environment
(adaptation) tend to survive,
& reproduce more
(“survival of the fittest”)
• What will that cause?
– favorable adaptation will be
passed to more offspring
than before
– acts on individuals, BUT
causes evolution of
population
4 Mechanisms of Evolution
•Which trait was a better
adaptation and selected for?
•How were frequencies of
different alleles affected?
Explanations for How Evolution Happens
• What did Jean Baptist Lamarck propose about how
evolution occurred?
– “Theory of Acquired Characteristics” (use vs. disuse)
• acquired traits are passed on & leads to changes in species
– Proposed that nature drove organisms from simple to
increasingly complex forms
• Did experimentation support Lamarck’s thinking?
–no
Explanations for How Evolution Happens
• Charles Darwin (naturalist on HMS Beagle)
– What did he do on his trip?
• collected fossils & specimens
– observed tremendous biodiversity
» noticed unique organisms similar to organisms in other
parts of world… determined they were all related
Climate varied from island to island.
intermediate shell
domed
Shell
large rainfall
saddlebacked
shell
desert
Explanations for Evolution
• What did Darwin conclude from his observations?
– life forms can & do change…. but, questioned how this
change occurred…
•“answers” pointed to evolution or “descent with modification”
–needed to test ideas before explaining how or why such changes happen
Explanations for Evolution
• When thinking about HOW
evolution happened, Darwin
noted artificial selection
(selective breeding)…
– plan/goal = to produce
preferred offspring
• Darwin wondered, “Is there a
force in nature that simulates
artificial selection???”
Darwin’s Explanation: Natural Selection
• What were the 4 main points
Darwin used to explain how
evolution occurred?
1859
1. Overproduction of offspring
2. Struggle to survive
(competition for existence)
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 offspring
will survive long
enough to reproduce
& pass on genes
Darwin’s Explanation: Natural Selection
2.
Over production leads to
the “struggle to
survive”… How?
– more organisms than
resources to go around leads
to competition (idea based on
work of Thomas Malthus)
• Organisms compete for…?
– food, shelter, mates, space, light,
water, nutrients, etc.
• Population levels off at the
“carrying capacity”.
– maximum # that can be supported
given available resources
Video: Darwin
& Malthus
Darwin’s Explanation: Natural Selection
•The survivors of the “struggle to survive”…
camouflage
– Who are they?
• individuals w/ variations that are best suited
for that particular environment (adaptations)
– How do they get these traits?
• chance & variation
– unlike artificial selection which has plan/goal
– Were these traits a response to their environment?
• NO… it just so happens that the variation is beneficial
– & allows for increased survival & reproduction of more offspring with
that trait (due to natural selection for that trait)
Darwin’s Explanation: Natural Selection
Darwin’s Explanation: Natural Selection
Contractile
Vacuole
Video
Darwin’s Explanation: Natural Selection
3. In any given population, there will be a variation
within a trait.
Darwin’s Explanation: Natural Selection
•What causes variations within a
population?
– Sexual reproduction
– Crossing over during meiosis
– Arrangement of chromosomes during
meiosis (independent assortment)
– Mutations
• Sexual repro. & meiosis speed up
evolution… increases variety
• Darwin did NOT have
knowledge of genetics!
Darwin’s Explanation: Natural Selection
4. How does natural selection lead to successful
reproduction?
– Those organisms best suited for environment tend to
survive, reproduce, & pass on genes (“survival of fittest”)
• more offspring have favorable adaptation than before
Darwin’s Explanation: Natural Selection
• Ex.  Pepper Moths – England
– Original color – 99% white (trees w/ light bark)
• Industrial Revolution, 1850s – produced soot
– Enviro. changes - 1890s - 99% black (trees w/ dark bark)
Pepper Moth “Game” http://www.techapps.net/interactives/pepperMoths.swf
Principles of Natural Selection "Interactive"
Darwin’s Explanation: Natural Selection
Adaptive
Radiation
Hawaiian Honeycreepers
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
• Who was Alfred
Wallace (1858)?
– naturalist that
arrived at same
basic explanation
as Darwin
• However, Darwin
usually given credit
– but BOTH men
should be credited
Indirect Evidence to Support the
Theory of Evolution: Fossil Record
• fossil record
– evidence of:
• change in organisms
over time
Which layer is youngest? oldest? Explain…
Law of Superposition
• age of the Earth
Indirect Evidence to Support the
Theory of Evolution: Fossil Record
• Why is the fossil record limited?
– decomposition
– type of material
•
What fossilizes best?
–
hard parts…. teeth, bones, scales
– incomplete record
•
Why?
–
–
not all organisms are fossilized
not all fossils are found
– easily disrupted
•
Why?
–
some are destroyed by natural processes or people
Indirect Evidence to Support the
Theory of Evolution: Comparative Anatomy
• comparative anatomy
– compares structures of different organisms living today
1. homologous structures
2. analogous structures
3. vestigial structures
Indirect Evidence to Support the
Theory of Evolution: Comparative Anatomy
• 1. What are “homologous structures”?
– similar structures with modifications (ex. location &
arrangement of bones)
•
Which are evidence of …?
–
–
a common ancestor
later organisms becoming more different (divergent evolution)
Indirect Evidence to Support the
Theory of Evolution: Comparative Anatomy
• 2. What are “analogous
structures”?
– different structure, but same
function (ex. wings made of
different materials… bird =
bone vs. insect = chitin)
• Which are due to…?
– similar environment/use
» but… do NOT have common
ancestor
» later organisms become more
similar (convergent evolution)
Indirect Evidence to Support the
Theory of Evolution: Comparative Anatomy
• 3. What are
“vestigial
structures”?
– structures with
reduced size or
function that
often have no
apparent use
• Which are
evidence
that…?
– species has
changed
Indirect Evidence to Support the
Theory of Evolution: Comparative Embryology
• How does embryonic
development provide
evidence for evolution?
– early stages 
very similar
• later stages 
more distinction
– What does this tell us?
» organisms inherited same
basic body plan from
common ancestor
» greater # similar stages 
more closely related
Indirect Evidence to Support the
Theory of Evolution: Comparative Biochemistry
• What codes for similar organic compounds
(ex. amino acids & proteins)?
– similar DNA
• 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
Direct Evidence to Support the
Theory of Evolution: Observation
• Ex. of rapid evolution that allow us to observe evolution…?
1.
antibiotic- resistant bacteria
•
2.
•
MRSA
pesticide-resistant insects
Resistance already present in some individuals (variation)
–
resulting from mutation
Evolution & Classification
• Evolutionary relationships
are the basis of classification
– closely related  share more
groups (similar classification)
• black bear & brown bear
– same down to genus
– distantly related  share
fewer groups (dissimilar
classification)
• snake & brown bear
– same only to phylum
DOMAIN
Eukaryota