Transcript Evolution ppt

Evolution
Darwin’s Theory of
Natural Selection
MAIN IDEA: Charles Darwin
developed a theory of evolution based
on natural selection.
Why was Darwin’s work
controversial?
Evolution vs. Creationism
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Creationism – belief that God
created all living things to be unique
Evolution – theory that organisms
have changed over time.
Until the 1800s
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People thought the same types of
organisms on earth were always in
existence
This changed when scientists found
fossils of organisms no longer on
earth
What made Darwin question
previous assumptions on how
different organisms came to be?
Scientists observed…
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Fossil evidence
Many different species
Variations (differences) within
species
Change in Thought
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Scientists began to wonder how and
why these changes took place
2 biologists believed organisms
changed in response to their
environments:
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French Jean Baptiste Lamarck
British Charles Darwin
Lamarck’s Theory
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1809 – Lamarck proposed his theory
of evolution
Theory based on 2 hypotheses:
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Organisms develop traits by the use
and disuse of body parts
Acquired characteristics – passed from
parents to offspring
According to Lamarck, why do
giraffes have long necks?
Lamarck’s giraffe example(Don’t
Copy)
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Lamarck assumed giraffes had short necks
originally and ate grass
Grass died due to climate change
Giraffes ate leaves off trees
As giraffes stretched necks, necks grew
Giraffe’s acquired long necks – passed to
future generations
Scientists questioned this theory…
Charles Darwin
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Born in 1809
Age 22, went on voyage on HMS Beagle
(British ship) as a naturalist
Mapping expedition of S. America and
S. Pacific
Darwin’s Thoughts (Don’t Copy)
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Charles Lyell’s book influenced Darwin Lyell said Earth was millions of years old
Observed fossils of marine animals on
mountains, etc
Observed changing earth: earthquakes,
volcanoes, etc; saw change in the land
Thought organisms would have to adapt to
these changes
Darwin’s Studies
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Observed thousands of different
species
Took careful notes
Collected specimens
Studies fossils
Galapagos Islands (Don’t Copy)
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Off coast of Ecuador
Observed MANY different species
Many similar to those on coast of S.
America
Observed tortoises, iguanas, finches, etc
with slight differences on different
islands
Ex: different beaks of finches
Help from Gould (Don’t Copy)
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John Gould, another British naturalist
Concluded finches were different
species, and were not on mainland of S.
America
Darwin though species changed after
reaching islands
DO NOW
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What is the difference between natural
selection and artificial selection?
What is the difference between natural
selection and evolution?
Artificial vs. Natural Selection
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Artificial - breeding for desired traits
Natural – naturally “desired” traits are
bred more often – causes gradual change
in species over time (evolution)
Darwin’s Theory
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Published book: On the Origin of Species
by Means of Natural Selection with help
from another scientist, Alfred Russel
Wallace
Theory based on 4 main ideas:
 Variations
 Inheritance of traits
 Overproduction
 Survival of the fittest
Variations
Variations (differences) occur among
members of the same species
 Ex: different breeds of dogs, horses, cats,
etc.
Inheritance of Variations
 Traits are inherited
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Overproduction
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Organisms produce more organisms than
can survive and reproduce
This ensures that some offspring will
survive to reproduce
Ex: fish, insects, frogs, etc.
Survival of the Fittest
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Organisms with traits that are better for
adapting survive to reproduce
Pass on these useful traits
Natural selection – environment
determines which variations will be
selected
Peppered Moth Example
(DON’T COPY)
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Early 1800s, England
Peppered moths were mostly light gray;
few were white, few were black
(variations)
Gray blended with tree trunks – birds
didn’t see or eat them, so they survived,
but black ones were eaten
Peppered Moth Cont’d
(DON’T COPY)
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Industrial Revolution – many factories
built
Black soot on trees
Which moths were NOW more likely to
survive?
Do Now
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Once, many years ago, horses were the
size of cats. Now, they are obviously
much bigger. How would Lamarck
explain this change? How would Darwin
explain it?
Evidence of Evolution
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Fossils
Anatomy
Embryos
Molecules
Biogeography
Fossil Evidence
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Show extinct species
Show relationships between current and
ancient organisms
Show intermediate species – those in
between ancient and modern species
Difference in traits – derived vs.
ancestral
Anatomical Evidence
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Similar structures found in closely related
species; have common ancestor
Diverse vertebrates have similar limb
structures, but may not have same function
–homologous
Vestigial structures – structures not
currently used by organism; evidence of an
organism’s evolutionary past Ex: hind
limbs of dolphins/whales
Homologous Structures
Homologous vs. Analogous
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Remember, homologous – similar
STRUCTURE
Analogous – structures with similar
FUNCTIONS, but different
structures/origins
Ex: bat’s wing and bird’s wing analogous
Evidence in Embryos
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Pattern of meiosis (gametes)  fertilization
 mitosis (adults)
All vertebrate embryos have homologous
structures that may not be in adults:
 Tails (most adults keep their tails!)
 Limb buds – become limbs
Vertebrates have a common ancestor
Molecular Evidence
DNA:
 Basic genetic code for each species
 Ex: humans all have same basic genetic
code
 Species that are similar have many
similarities in their DNA
 Species with a more distant ancestor
have more differences in DNA
Molecular Evidence
Proteins:
 Because of similar DNA, organisms of
the same species have the same basic
proteins
 Similar species – similar amino acid
sequences in their proteins
Biogeography
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Study of distribution of organisms on
earth
Similar environments lead to similar
adaptations in organisms, even if far
apart
Adaptations
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Traits that allow for survival
Fitness – way to measure how effective
traits are
Examples of adaptations:
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Camouflage
Mimicry
Remember that…
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Not all traits evolve slowly; Ex: bacteria
Not all traits increase fitness
Mutations can be a source of new traits
Evolution and Genetics
Population
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Members of same species living in same
area
All genes in a population = gene pool
Population Genetics
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Allele frequency – percent of certain alleles
(gene types) in a population’s gene pool
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Ex: all homozygous red flowers have a 100%
frequency for red alleles
Usually remains stable in a population
Changes in the Gene Pool
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Changes can occur in the gene pool, which
could cause evolution
Kinds or percentages of genes can change
4 things cause these changes
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Natural selection
Mutation
Migration
isolation
4 Factors Change the Gene Pool
1. Natural selection
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Well-adapted organisms survive to reproduce
Pass on genes to next generation, increasing
the gene frequency
4 Factors Change the Gene Pool
2. Mutation
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Adds a new gene to the gene pool
Can cause small, immediate change, or go
undetected for generations
Can be helpful, harmful, or neutral
4 Factors Change the Gene Pool
3. Migration
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Movement of organisms into or out of a
population
Causes gene flow – movement of genes in
or out of populations
4 Factors Change the Gene Pool
4. Isolation
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Organisms become separate from other
organisms (geographic isolation)
Caused by physical barriers, natural
disasters, etc
Causes speciation
Causes reproductive isolation between the
now separate species
Create
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With your group, pick any species, and
create a scenario as to how it may evolve
based on your assigned factor. Base your
predictions on facts about the species.
Describe and/or draw your predictions,
and then present to the class!
The Rate of Evolution
Gradualism
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Evolution through slow change
Believed to be true by Darwin and many
other scientists
Fossil evidence supports this
Punctuated Equilibrium
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Species remain unchanged for thousands
of years, then suddenly undergo rapid
changes
Fossil evidence of trilobites – unchanged
for millions of years, then suddenly died
off