Download Evolution by Natural Selection

In your notebook, copy and answer the
following questions:
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What percent of human and ape DNA is identical?
We have evidence for evolution. True or False?
Scientists agree on all aspects of evolutionary theory. True or False
The fossil record supports the theory of evolution. True or False
Evolutionary theory teaches that humans evolved from apes. True or
False
Mutation is a driving force for evolution. True or False
Species can change over time. True or False
Individual organisms can evolve. True or False
How old is the earth?
Evolution cannot be observed. True or False
Evolution is still occurring. True or False
Evolution leads to the eventual formation of a perfect organism.
True or False
Answers
• What percent of human and ape DNA is identical? At least 98%
(with chimps it’s around 98.8%) – we share about 55% with a
banana
• We have evidence for evolution. True
• Scientists agree on all aspects of evolutionary theory. False
• The fossil record supports the theory of evolution. True
• Evolutionary theory teaches that humans evolved from apes. False
• Mutation is a driving force for evolution. True
• Species can change over time. True
• Individual organisms can evolve. False
• How old is the earth? 4.6 billion years
• Evolution cannot be observed. False
• Evolution is still occurring. True
• Evolution leads to the eventual formation of a perfect organism.
False
Unit 4 Notes
Evolution by Natural Selection
Change over Time
Overview
• Remember, a theory isn’t “just
a theory” in science – it
provides an explanation for a
natural phenomenon based on
observations;
– they have been repeatedly
tested and proven to be
true (think of the theory of
gravity, the atomic theory,
or the cell theory)
• The theory of evolution states
that all organisms on Earth
have descended from a
common ancestor
Key Understandings
• Modern species developed from past species.
• Mutations in DNA create new traits.
• Beneficial traits get passed down through
generations.
• The environment “selects” who reproduces
and who dies.
Key Understandings cont. Evolution is Slow
• Earth is approximately
4.6 billion years old.
• Earliest forms of life
appear 3.5 billion years
ago (cyanobacteria)
• Modern humans appear
10 thousand years ago.
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Early Ideas
Spontaneous generation – one of the
earliest ideas about the origin of life
– Belief that life arises from nonlife
– Ex – people thought that flies came
from dead meat, or that mice were
created by putting damp hay in a dark
corner, or mud could give rise to worms
– Not completely rejected until the mid
1800’s
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Louis Pasteur designed an
experiment to show that living
organisms are what produce other
living organisms (called biogenisis)
– Used flasks filled with nutrient broth –
one exposed to air and another sealed
shut; nothing grew in the sealed
container, but the open container had
microorganisms begin to appear
Charles Darwin
• Traveled to South America in
1835 on the HMS Beagle.
• Visited the Galapagos Islands.
• Was the naturalist - collected
fossils, plants, and animals.
• Wrote “On the Origin of Species
by Natural Selection.”
• When he boarded the HMS
Beagle in 1831, the average
person thought that the world
was 6000 years old and that
plants and animals were
unchanging
Darwin cont.
• The voyage took 5 years
• When they reached the
Galapagos Islands, Darwin saw
that on the 4 islands he visited,
they each had their own, slightly
different varieties of animals
• After studying the finches he
collected, he discovered that they
were different from finches
anywhere else in the world
• perhaps they were blown off
course during migration – closely
resembled main land species (in
south america)
Activity – turn to your partner and discuss the
following questions
• These are all types of
finches Darwin
encountered on his
voyage
• Based on their beak
shape, what type of
food do you think each
bird most likely ate?
• How could natural
selection result in the
different beak shapes
seen in the Galapagos
finches?
Darwin Cont.
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Darwin hypothesized that new species
could appear gradually through small
changes in ancestral species, but he
wasn’t sure how that process would work
He turned to animal breeders (pigeons
specifically) for help
Different breeds of pigeons have distinct
traits that are present in their offspring – a
breeder can selectively breed those
pigeons to promote those traits
This process of breeding desired traits is
called artificial collection (also occurs with
dogs or crops or livestock)
Darwin inferred that if humans could
change species by artificial selection, then
maybe the same process could work in
nature and perhaps create a new species
– but it would take time because the
changes were due to chance (remember,
most people believed the Earth was only
6000 yo).
Darwin Learned from Geologists…
• Darwin learned the
earth was much older
than originally thought,
which supported
Darwin’s theory that
populations changed
very slowly, requiring a
lot of time
Darwin learned from Thomas Malthus
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Darwin read an essay by economist
Thomas Malthus, which stated that
the human population, if unchecked,
would eventually outgrow its food
supply, leading to a competitive
struggle for existence
Darwin realized that this could be
applied to the natural world, since
other animal species were capable of
producing too many offspring.
Starvation, disease, and predators
affected the population, leaving only
the most fit and adapted alive
This is the process of natural
selection – the framework for the
theory about the origin of the species
Darwin cont.
• Evolution is now used
to define cumulative
changes in species over
time, while natural
selection is one way it
can occur
Natural Selection
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Darwin's theory of natural selection
has 4 basic principles that explain
how traits of a population can change
over time.
First – individuals in a population
show differences (variation)
Second – variations an be inherited
(from parents to offspring)
Third – organisms have more
offspring than can survive on
available resources
Fourth – variations that increase
reproductive success will have a
greater chance of being passed on
than those that don’t
Activity
• A fictional (made-up) crevice lizard lives in cracks in rocks.
Freezing and thawing have widened these cracks, and lizards
that are now in large crevices are more easily captured and
eaten.
• With your table partners, use the principles of natural
selection, predict how future generations of the crevice lizard
population will change over time.
• Draw a picture of your lizard, and give 3 examples of how it
has adapted to its environment to best survive.
Evidence of Evolution
• The fossil record: shows that ancient species
share similarities with modern species.
Transitional Fossils
• Provide proof of
intermediate species.
• Example: Archaeopteryx
• Transitional organism.
Shows characteristics of
both dinosaurs and
birds.
• Feathers: Derived traits
(new)
• Teeth and bony tail:
Ancestral (old)
Evidence of Evolution
• Comparative Anatomy: using form to
determine ancestry.
Homologous Structures
• Anatomically similar structures inherited from
a common ancestor.
Analogous structures
• Can be used for the same purpose, may look
similar, but are NOT inherited from a common
ancestor.
Vestigial Structures
• Reduced forms of once functional structures.
No longer used?
Evidence of Evolution
• Comparative
Biochemistry
• DNA and RNA
• Form the molecular
basis of heredity in all
living things.
• Organisms with similar
anatomical features
also show similar
molecular features. Ex.
Chimps and Humans
REMEMBER!
• A theory isn’t “just a theory”
in science – there is A LOT of
evidence required and it must
be proven to be true over and
over for a hypothesis to
become a theory.
Evolution Essay
Please write a short essay (a few paragraphs)
in your notebook that explains why the
organism on the next slide can live where it
does. Please use the following key words in
your argument:
Natural Selection
Characteristics
Evolution
Environment
Fitness
Adaptaiton
Mountain Goat