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The Theory of Evolution
In science, theories are statements or models that have been tested and
confirmed many times.
Theories have some important properties:
They explain a wide variety of data and observations
They can be used to make predictions
They are not absolute, they serve as a model of understanding the
world and can be changed as the world view changes
In science, the term "Theory" does not express doubt.
In science, the term theory is used to represent ideas and explanations that
have been confirmed through tests and observations
The theory of evolution remains one of the most useful theories in biology
because it explains many questions and observations.
Some questions that can be answered by evolution:
Why do so many different animals have the same structures, the arm
bones in a human are the same bones as a flipper in a whale?
Why do organisms have structures they no longer use, like the
appendix in a human? Non functioning wings in penguins
Why are there bones and fossil evidence of creatures that no longer
exist? What happened to these creatures?
Why do so many organisms' morphology and anatomy follow the same
Why is the sequence of DNA very similar in some groups of organisms
but not in others?
Why do the embryos of animals look very similar at an early stage?
The Theory of Evolution is considered a Unifying Theory of
Biology, because it answers many of these questions and offers
and explanation for the data.
Lamarck's Theory of Acquired Characteristics
Lamarck thought that you would gain or lose
features if you overused or didn't use them, and you
could pass these new traits onto your offspring.
This was known as the Inheritance of Acquired
A lizard that didn't use it legs would
eventually not have legs and its offspring wouldn't have legs
A giraffe stretched its neck to reach higher leaves, and this stretched
neck would be a trait inherited by its offspring
Lamarck's Theory was eventually discarded - PROVEN TO BE WRONG!
Why? Logically it doesn't work. Imagine if you were in a car accident and had
a leg amputed. This does not mean that your children will only have one leg.
Features gained during life are not passed on to children.
Darwin's Theory of Evolution by Natural Selection
Darwin was a naturalist who observed many species. He is famous for his trips
to the Galapagos Islands, his observations of the finches (and other animals)
and the book he wrote: "The Origin of Species”:
There are four parts of natural selection:
1. Variation exists among individuals in a species.
2. Individuals of species will compete for resources (food and space)
3. Some competition would lead to the death of some individuals while others
would survive
4. Individuals that had advantageous variations are more likely to survive and
The favorable variations are called Adaptations.
Darwin's Finches:
Darwin noted that all the finches on the galapagos
island looked about the same except for the shape of
their beak. His observations lead to the conclusion
that all the finches were descendents of the same original
population. The shape of the beaks were adaptations for eating a
particular type of food (Ex. long beaks were used for eating
insects, short for seeds)
Evidence of Evolution
1. Fossils
Fossils are the remains or impressions left by plants or animals that
lived a very long time ago.
Fossils may look the same as when the plant or animal was alive but
have now changed to stone.
If today's species came from ancient species, then we should be able to
find remains of those species that no longer exist.
We have tons of fossils of creatures that no longer exist but bear
striking resemblance to creatures that do exist today.
Carbon dating--gives an age of a sample based on the amount of
radioactive carbon is in a sample.
Fossil record- creates a geologic time scale.
2. Anatomy
Homologous Structures-- structures that are similar in origin, but have
different functions.
o Example: The wing of a bird and the forearm of a human
Analogous Structures-- structures that are not similar in origin, but
have same functions.
o Example: The wing of a bird and the wing of a butterfly.
Vestigial Organs-- seemingly functionless parts, snakes have tiny
pelvic and limb bones, humans have a tail bone
3. Embryology
Embryological development--Embryos of different species develop
almost identically
4. DNA
Evidence of Common Ancestry -- organisms that are more distantly
related would be expected to accumulate a greater number of
evolutionary differences, whereas two species that are more closely
related should share a greater portion of their DNA.
The Theory of Evolution Guided Reading Questions
Answer the following questions on a separate sheet of paper. Please restate.
In science, what are theories?
What are the three important properties of theories?
In science, the term theory is used to what?
What theory remains one of the most useful theories in
biology because it explains many questions and
5. List 3 questions that can be answered by evolution?
6. Lamarck’s theory related to evolution was called Inheritance
of Acquired Characteristics. Describe his theory and what he
7. Describe one example of Lamarck’s Inheritance of Acquired
8. Eventually, what happened to Lamarck’s theory and why?
9. Darwin was a naturalist who observed many species. Where
did Darwin observe finches and many other animals to create
his ideas for the theory of evolution?
What was the book called that Darwin wrote about
List the four parts of Natural Selection.
What are adaptations?
Darwin noted that all the finches on the Galapagos
island looked about the same except for the shape of their
beak. What was the conclusion he came up with based on his
What are the 3 types of evidence of evolution?
What are fossils?
What is the difference between homologous and
analogous structures? List one example for each. ``
What are vestigial organs?
List an example of a vestigial organ.
Describe embryology.
How is DNA evidence of evolution?