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DNA
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Take out Timeline & pink sheet if it is
complete
Take out or get a pencil
Clear your desk
 SMILE!
Theories of Evolution
The Historical Perspective
What is a theory?

A well-supported testable explanation of
phenomena that have occurred in the natural
world.
Views of Life on Earth Prior
to 1800

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Aristotle’s ideas
prevailed
Throughout the history
of life on Earth, species
were unchanging
Theory of Acquired Traits
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
Proposed by Jean Lamarck
(1744-1829)
Species change from
generation to generation
through the use and disuse of
organs and appendages
Theory of Acquired Traits
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Short necked giraffes
stretched their necks to
feed higher in the trees
This made their necks
longer
When they reproduced,
their offspring would also
have longer necks
Suggestions of Theory
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Women that dyed their hair blonde
would have blonde children
A person with an amputated leg would
have children without that same leg
Could traits be inherited in
this manner?
The answer is obviously NO.
Today we know that Lamarck’s theory was
a misconception.
The Theory of Natural
Selection (1859)

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Proposed by Charles
Darwin (1809-1882)
Organisms with
favorable variations
survive, reproduce, and
pass the traits on to the
gene pool
How did Darwin formulate
his theory?
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At the age of 22, Darwin was offered an
opportunity to join the crew of a ship,
the H. M. S. Beagle
The ship’s mission was to chart the
coasts of South America
Darwin was the ship’s naturalist
The Beagle Sets Sail

The Beagle leaves
England in 1831
The Fantastic Voyage of the HMS Beagle
Entries from Darwin’s Journal
Entries from Darwin’s Journal
Returning to England, 1836
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Darwin spent the
next 22 years
studying his
collections and
conducting
experiments
Darwin Published his Theory
in 1859
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Using the data he
gathered from his
voyage, Darwin
formed his well known
idea and published his
theory on natural
selection
Darwin’s Major
Findings
Smaller tortoises with long
necks were found where there
was higher growing plants
 The Dryer Regions
 Larger tortoises with short
necks primarily fed on grasses
and low vegetation
 The more lush Regions

Large Ground Finch
Warbler Finch
Small Tree Finch
Finches
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Like the tortoises the birds also “fit” their
habitats
Their beaks ranged in size and shape and
these shapes and sizes were perfect for their
diets.
13 different species that fit into their own
niche
Mechanisms of Natural
Selection
1.
2.
3.
4.
Overproduction
Competition
Variation
Survival of the Fittest
Mechanisms of Natural
Selection
1.
2.
3.
Overproduction—many offspring are
produced
Competition—struggle for limited
resources
Variation—variety exists in organisms
within a species (size, color, behavior)
Mechanisms of Natural
Selection
4.
Survival of the fittest—organisms best
adapted to the environment will survive.
They will pass on genes for this trait to
their offspring. The species will
become more “fit.”