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Natural Selection and the
Evidence for Evolution
Galapagos tortoises are the largest on Earth
Differing from other tortoises in body size and shape
The beak of this Galapagos finch
Is adapted to feed on cacti
Galapagos marine iguanas eat algae
Fro the ocean, an unusual food source
For reptiles. Large claws help them
cling to slippery rocks.
~ Studying the specimens
made Darwin curious
about possible
relationships among
~ His studies provided the
foundation for his
theory of evolution by
natural selection
I. Darwin Explains Natural Selection
A. In nature, organisms
produce more offspring
than can survive. Fishes, for
example, can sometimes lay
millions of eggs.
B. In any population,
individuals have variations.
Fishes, fore example, may
differ in color, size, and
C. Individuals with certain
useful variations, such as
speed, survive in their
environment, passing those
variations to the next
D. Over time, offspring with
certain variations make up
most of the population and
may look entirely different
from their ancestors.
~ Natural Selection is a mechanism for
change in population.
~ It occurs when organisms with favorable
variations survive, reproduce, and pass
their variations to the next generation.
Purpose: Make the following foldable to help you
analyze and critique evidence supporting the
theory of evolution
~ Structural adaptations
as the teeth and
claws of mole-rats are
often used to defend
against predators.
~ Some adaptations of
other organisms that
keep predators from
approaching include a
rose’s thorns or a
porcupine's quills.
~ these may take
Millions of years
To develop.
Some adaptations are subtle.
Mimicry is a structural adaptation that enables
one species to resemble another species.
Another subtle adaptation is camouflage, an
adaptation that enable species to blend with
their surroundings
Structural Adaptations arise over time
According to Darwin’s theory, adaptations in
species develop over many generations.
Dot Demonstration:
Using the white paper, use the hole punch to make
a minimum of 20 holes.
Using the black paper, use the hole punch to make a
minimum of 20 holes.
(follow teacher verbal direction)
~ Physiological adaptations can develop rapidly.
~ Physiological adaptations are changes in an
organisms metabolic processes.
Kudzu: plant that grows 12 inches each day.
Does not take over or kill anything, competes for
sunlight from other
Antibiotics can be used
So much that bacteria become
Familiar with its response,
Changing how it operates
~ Fossils provide a record of early life and
evolutionary history.
~ Example: Fossils of whale ancestors were
probably land-dwelling, doglike animals.
~ Although the fossil record provides evidence that
evolution occurred, the record is incomplete.
~ Even though they do not have all the fossils for all the
animals they can understand an overall picture of how
most groups evolved.
~ Looking at the anatomy of organisms, biologist can
view structural similarities as evidence that organisms
evolved from a common ancestor.
~ It would be unlikely for so many animals to have
similar structures if each species arose separately.
~ Homologous structures are features with a
common evolutionary origin.
~ Similar in arrangement, in function or in both.
~ The structural or functional similarity of body feature
doesn’t always mean that two species are closely
related. These are analogous structures.
~ The body parts of organisms that do not have a
common evolutionary origin but are similar in function
are called analogous structures.
~ Embryo is the earliest state of growth and
development of both plants and animals.
~ At this stage all embryos have a tail and pharyngeal
~ In fish these pouches form into gills but in mammals,
reptiles and birds they develop into ears.
~ Biochemistry provide strong evidence for evolution.
~ Nearly all organisms share DNA, ATP and many
enzymes among their biochemical molecules.
~ Groups that share more similarities are interpreted as
being more closely related or as sharing a closer
Homework questions
1. Briefly explain Darwin’s ideas of natural selection.
2. Some snakes have vestigial legs (legs during embryo
but not when born). Why is this considered
evidence for evolution?
3. Explain the difference between mimicry and
camouflage. Now explain how it helps them to
4. How do homologous structures provide evidence
for evolution?