Download Darwin`s Observations

Today’s Agenda…
Bellringer: 5 MC on Physical Science
– Motion and Forces
 Take up HW
 Notes on Darwin’s Voyage SP#1
 Homework
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Today’s Targets… 
I can explain how and why species
adapt to their environment.
 I can explain how natural selection
accounts for the diversity of species.
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Darwin’s Observations
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Living things are very diverse
There are over 1.7 million species of
organisms
A species is a group of similar organisms
that can mate with each other and
produce offspring
Characteristics of species are inherited as
genetic information is passed from parent
to offspring
Darwin’s Observations
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Darwin saw many unusual
organisms on the Galapagos Islands
Giant land turtles
 Seals covered with fur
 Lizards that ate cactus plants
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Darwin’s Observations
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Many of the animals on the island
were similar to animals on the
mainland, but had important
differences
Darwin’s Observations
Darwin concluded that the animals
had came from the mainland,
reproduced, and became different
from their relatives
 There were even differences
between species as he traveled from
one island to the next
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Example: the shells of tortoises, finch
beaks
Adaptations
Page 336 Figure 3
 Finches on the Galapagos Islands
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Varied sizes and shapes of beaks
 Each species was well suited to the life
it led
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• Finches that ate nuts and seeds had strong,
wide beaks
• Finches that ate insects had long, slender
beaks
Adaptations
Beak shape is an example of an
adaptation
 Adaptation: a trait that helps an
organism survive to reproduce and
pass on its traits
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Evolution
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Darwin continues to think about his research
He concluded that animals on the island were
faced with different conditions than they had
been on the mainland
Darwin thought the species gradually changed
over many generations and became better
adapted to new conditions
Evolution is the gradual change of species over
time
Darwin wasn’t sure how this process had
occurred, so he looked at more examples
Evolution
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Darwin considered the process of
selective breeding to create offspring with
certain traits
What is selective breeding?
Darwin proposed that a process similar to
selective breeding must occur in nature
But why were certain traits selected and
how?
Natural Selection
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Darwin’s explanation for how evolution
occurs
Explained in his book The Origin of
Species
The process by which individuals that are
better suited to their environment are
more likely to survive and reproduce than
others
Natural Selection
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Factors that affect natural selection:
Overproduction
 Competition
 Variation
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Natural Selection
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Overproduction
Species produce more offspring than
can survive
 There are not enough resources – food,
water, living space
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Natural Selection
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Competition
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Since resources are limited, the
offspring must compete to survive
Natural Selection
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Variations
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Any difference between individuals of
the same species
Natural Selection
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Some variations make certain
individuals better adapted to the
environment
More likely to survive and then
reproduce
 Offspring inherit the helpful trait and
pass it on to their offspring
 Page 338, Figure 4
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Natural Selection
The environment has “selected”
organisms with helpful traits to act
as parents of the next generation
 Page 337 –
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Table 1
 Applying Science
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Natural Selection
Over a long period of time, natural
selection can lead to evolution
 Helpful variations increase, while
those that are not helpful disappear
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