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Evolution
Georgia Performance Standards:
SB5b: Explain the history of life in terms of
biodiversity, ancestry, and the rates of evolution.
SB5d: Relate natural selection to changes in
organisms.
Essential Questions:
1.
2.
3.
Why is it important to understand evolutionary theory?
What is the role of natural selection in speciation?
Why are there species alive now that were not found in the past fossil
record?
4. How do fossil and biochemical evidence support the evolutionary
theory?
Bell Work:
1. What would you
say is the most
noticeable feature
on this bird?
2. What are some
possible advantages
this feature gives the
bird? What are some
disadvantages?
3. What changes
might increase this
bird’s ability to
survive and
reproduce? Explain
your answer.
What scientific explanation can
account for the diversity of life?
• Answer: The evolutionary theory
• Evolution, or change over time, is the
process by which modern organisms have
descended from ancient organisms.
• A theory is a well-supported testable
explanation of phenomena that have
occurred in the natural world.
Charles Darwin
• During his travels, Darwin made numerous
observations and collected evidence that
led him to propose a revolutionary
hypothesis about the way life changes
over time.
• That hypothesis, now supported by a huge
body of evidence, has become the theory
of evolution.
Darwin’s Observations:
• Patterns of Diversity - the many ways in which
organisms survived and produced offspring.
• Living Organisms and Fossils - Why had so
many of these species disappeared? How were
they related to living species?
• The Galápagos Islands - The higher islands
had greater rainfall and a different assortment of
plants and animals
Giant Tortoises of the Galápagos
Section 15-1
Islands
Pinta
Pinta Island
Tower
Marchena
Intermediate shell
Fernandina
James
Santa Cruz
Isabela
Santa Fe
Hood Island
Floreana
Isabela Island
Dome-shaped shell
Hood
Saddle-backed shell
Understanding Evolution: Problem-based discussion
Natural selection in Darwin’s finches
1) What characteristics of the graphs
show that there was variation in the
population? How much variation was
in the population in 1976? How much
variation was in the population in
1978?
2) What happened to the population
size between 1976 and 1978? What
other changes occurred in the
population?
3) Based on the data, what is the
approximate average beak depth of
the population in each year?
Ribozyme structure comes from Scott, W.G., Finch, J.T., Klug, A. (1995) The crystal structure of
an all-RNA hammerhead ribozyme: a proposed mechanism for RNA catalytic cleavage. Cell 81:
991-1002
Understanding Evolution: Problem-based discussion
Natural selection in Darwin’s finches
4) Based on these limited data,
which mode of selection seems to
have operated on the finches? What
evidence supports this idea?
5) What do you hypothesize could
have caused this change between
1976 and 1978? Describe a possible
ecological relationship between
drought and beak size.
6) Assume the drought continues for
another 2 years,. If natural selection
is occurring, what would you expect
to see in future generations? If the
changes in beak size are not due to
natural selection, but to drift, then
what would you expect to see in
future generations?
Ribozyme structure comes from Scott, W.G., Finch, J.T., Klug, A. (1995) The crystal structure of
an all-RNA hammerhead ribozyme: a proposed mechanism for RNA catalytic cleavage. Cell 81:
991-1002
Ideas That Shaped Darwin's Thinking
• Hutton’s Theory of Geological Change
– proposed that Earth had to be much more
than a few thousand years old.
• Lyell’s Principles of Geology
– Lyell’s work explained how awesome
geological features could be built up or torn
down over long periods of time.
– Lyell helped Darwin appreciate the
significance of geological phenomena that he
had observed.
Ideas That Shaped Darwin's Thinking
• This understanding of geology influenced
Darwin in two ways.
1. If Earth could change over time, might life
change as well?
2. Darwin realized that it would have taken
many, many years for life to change in the
way he suggested.
Ideas that shaped Darwin’s Thinking:
• Lamarck proposed that
by selective use or disuse
of organs, organisms
acquired or lost certain
traits during their lifetime.
– These traits could then
be passed on to their
offspring.
– Over time, this
process led to change
in a species.
– Lamarck’s ideas were
incorrect in several ways
(he did not know how traits
are inherited)
– He did not know that an
organism’s behavior has no
effect on its inheritable
characteristics.
– Lamarck was one of the
first to develop a scientific
theory of evolution and
realize that organisms are
adapted to their
environments.
– He paved the way for the
work of later biologists.
Ideas that Shaped Darwin’s Thinking
• Malthus & Population Growth reasoned that if the human population
continued to grow unchecked, sooner or
later there would be insufficient living
space and food for everyone.
Checkpoint Questions:
1. What two ideas from geology were important to
Darwin’s thinking?
2. According to Lamarck, how did organisms
acquire traits?
3. According to Malthus, what factors limited
population growth?
4. Why has Lamarck’s theory of evolution been
rejected?
5. Malthus formed his theory by studying factors
that control the population growth of humans.
How might factors operating on organisms in
nature differ from those of Malthus’s theory?
Darwin’s Conclusions:
• On the Origin of Species.
– In his book, he proposed a mechanism for
evolution that he called natural selection.
– He then presented evidence demonstrating
that the process of evolution has been taking
place for millions of years—and continues in
all living things.
Darwin’s Conclusions:
• Natural variation, defined as differences
among individuals of a species, is found in
all types of organisms. Variation is present
in species in nature
• Artificial selection, nature provided the
variation among different organisms, and
humans selected those variations that they
found useful.
Darwin’s Conclusions:
• Evolution by Natural Selection
– struggle for existence means that members of each species
compete regularly to obtain food, living space, and other
necessities of life.
– The ability of an individual to survive and reproduce in its specific
environment fitness, which is the result of adaptations.
– An adaptation is any inherited characteristic that increases an
organism’s chance of survival.
– Successful adaptations enable organisms to become better
suited “Fit” to their environment and thus better able to
survive and reproduce .
Darwin’s Conclusions:
• Individuals that are better suited to their
environment—that is, with high levels of fitness—
survive and reproduce most successfully.
• This was a process that Darwin called survival of the
fittest.
• Because of its similarities to artificial selection, Darwin
referred to the survival of the fittest as natural selection.
– In both artificial selection and natural variation, only
certain individuals of a population produce new
individuals
Darwin’s Conclusions:
• Over time, natural selection results in
changes in the inherited characteristics of a
population.
• These changes increase a species’ fitness in
its environment.
– Natural selection cannot be seen directly; it can only
be observed as changes in a population over many
successive generations.
Summary of Darwin’s Theory
•
•
Natural Selection is
always taking place:
Because more organisms
are produced than can
survive, members of each
species must compete for
limited resources.
Struggle to survive:
Because each organism
is unique, each has
different advantages and
disadvantages in the
struggle for existence.
•
Variation among
offspring: Individual
organisms in nature differ
from one another. Some
of this variation is
inherited.
•
Living things
overproduce: Organisms
in nature produce more
offspring than can
survive, and many of
those that survive do not
reproduce.
Summary of Darwin’s Theory
• Individuals best suited to their environment
survive and reproduce most successfully.
• Species change over time.
• Species alive today have descended with
modifications from species that lived in the
past.
• All organisms on Earth are united into a single
tree of life by common descent.