Transcript Chapter 5: Changes over Time Who was Charles Darwin?

Evolution by Natural
Selection
What is a species?

A group of
similar
organisms that
can mate with
each other and
produce fertile
offspring
What did Darwin notice on the
Galapagos Islands?


Many of the plants and
animals on the
Galapagos were similar
to organisms on
mainland South
America
However, there were
also important
differences between
the organisms on the
islands and those on
the mainland
Look at figure 2 on page 174
What did Darwin conclude led to the
differences between species?
After studying the
different finches on
the Galapagos Islands
Darwin concluded that
their different beak
shape was due to an
adaptation
 Adaptation – A trait
that helps an organism
survive and
reproduce


A. What types of things
would bird number 1
eat?

B. 2?

C. 3?

4. 4?
What did Darwin start to believe was
occurring amongst the different species?
Darwin thought the
species gradually
changed over
many generations
and became better
adapted to the
new conditions
 Evolution – the
gradual change in a
species over time

Why was Darwin’s idea considered a
scientific theory?
 It
was a well-tested concept
that explains a wide range of
observations
Think Pair Share
What
did Darwin discover on
his voyage to the Galapagos
Islands that led to his theory
of evolution?
Darwin and Alfred Russell eventually
proposed an explanation for how evolution
occurs in a book called what?
 The
Origin of
Species
 This
book
explained that
evolution
occurs by means
of natural
selection
What is Natural Selection?

The process by
which individuals
that are better
adapted to their
environment are
more likely to
survive and
reproduce than
other members of
the same species
What are the factors that affect the
process of natural selection?
 Overproduction
 Competition
 Variations
 Selection
How does overproduction affect
natural selection?
 So
many species
are produced
that there are
not enough
resources (food,
water, and living
space)
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How does competition affect natural
selection?
 Since
food and
other resources
are limited, the
offspring must
compete in
order to survive
How do Variations affect natural
selection?
Any difference
between individuals of
the same species is
called a variation
 Some variations of a
species may provide
an advantage over
the other members of
the species without
the variation

Think Pair Share
Differentiate
between
adaptation and variation.
How does the environment select
which organisms survive?


Individuals that are better
adapted to their
environment are more
likely to survive and
reproduce passing on the
helpful trait to the next
generation
In effect, The
environment “selects”
those organisms with
helpful traits to be the
parents of the next
generation
How is natural selection related to
evolution?
 Over
a long period of time,
natural selection can lead to
evolution
 Helpful variations gradually
accumulate in a species,
while unfavorable ones
disappear
What role do genes “play” in
evolution?
Darwin did not know
anything about genes or
mutations so he could
not explain what caused
the variations or how
they were passed on
 Only traits that are
inherited, or controlled
by genes, can be acted
upon by natural selection

Rate Yourself
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4 Apply concepts of natural
selection and evolution by creating a
scenario that demonstrates the ideas
3 Explain how natural selection
leads to evolution.
2 Describe how the evidence
supports evolution.
1 Identify evidence for evolution.