Evolution and Natural Selection by wulinqing


Traits are passed from parent to offspring
        during the process of sexual

Usually, each offspring inherits genes that
         are made of the same DNA
However, mutations, or changes in an organism's
 DNA that occur during meiosis may result in an
  offspring receiving a different form of a trait
          than what their parents had.

  Over long periods of time, these changes may
              result in EVOLUTION
           Charles Darwin
One of the most famous and most controversial
           scientists of modern times.
• Collected animals, plants, and fossils from many
  countries during a 5 year voyage around the world
  on a ship called the H.M.S. Beagle
He wanted to explain why living things
were so diverse…
• Darwin made many interesting discoveries
  during his journey
• Helped him understand living things are so
  diverse because they change over time
• Darwin found that organisms in
  different parts of the world had similar
  traits if they lived in similar
• Similar traits are helpful in similar
      The Galapagos Islands
Group of islands near South America where
 Darwin made one of his most important
     To Finch or not to Finch…
• A variety of finches on the islands were similar to a
  species found in South America.
    Something smells Finchy?
• Each had a different beak that Darwin thought
  was used to eat a different type of food

• Some could crush seeds; others could grab
              Finch Evolution
Darwin predicted the finches originally came from South
America, and changed over time because of the
environment of the island

• Each finch evolved an adaptation that allowed it to eat
a different type of food
Evolution is change in a species observed over time

An Adaptation is a trait that allows an organism to
survive in its environment
           The Beginning…
After analyzing his data, Darwin wrote a book
 which described his theory of evolution by
 natural selection called On the Origin of
       Scientific Controversy
• Before Darwin's work, many scientists already
  accepted evolution, but did not agree on how it

• Darwin provided more evidence that evolution

• Darwin also explained how evolution occurred

• Many scientists agreed, while many disagreed
          Natural Selection
How evolution works according to Darwin.
• An organism's environment is always changing
• Only certain organisms can survive in certain
  environmental conditions
      Four parts of Natural
There are four main parts of natural selection

Part 1:Variation - All organisms are different.
These differences may result from three things:
• Mutations in DNA
• Random sperm fertilize random eggs during
  sexual reproduction
• Crossing-over during meiosis
Part 2: Struggle for Existence - All organisms compete
to survive
• Not all organisms can win
Part 3: Survival of the Fittest - Only the best adapted
organisms will survive and reproduce
Part 4: Evolution – As the best adapted organisms
reproduce, the best traits are passed on to each

• Evolution occurs because the organisms change
   over time
• As organisms change, new species are formed

      A species is a group of organisms that can
          reproduce and create fertile offspring
• New species are formed when organisms cannot
reproduce with each other (three reasons)
• Location, time and behavior
Peppered Moths in England
           Evidence for Evolution
Many scientists have spent their entire lives looking for
 evidence to support evolution.

A wide variety of evidence exists in many forms.

Fossil Records – Fossils are studied and compared to
  organisms that are alive today
Fossils are the remains of organisms that lived millions
of years ago
           Transitional Forms
Organisms with a mixture of traits that belong to two
different types of organisms.

     Examples: Acanthostega: a mixture of Fish
     and amphibians
Fin/Limb Comparison

FISH          Acanthostega
Archaeopteryx: a mixture of reptiles and birds
Ambulocetus: a mixture ofland mammalsand
           Why Study Fossils?
• Provide evidence that organisms slowly change over
• Act as links that complete the chain of evolution by
natural selection
            Why Compare?
Comparing Organisms – If organisms share traits
 they might be related by evolution.

Homologous Structures - Share a common origin,
 but do not always share a common function

    Examples: the arm of a human; the fin of a
    dolphin; the wing of a bat; and the wing of a
They are made of the same bones, but each was
changed to fit the conditions of a different
      Analogous Structures
Analogous Structures - Share a common function,
but never share a common origin
     Example: the wings of a bird and the wings of
     a dragonfly
Both are used for flight, but are not made of the
same parts
• The organisms are not related because these
structures do not share a common origin
          Vestigial Structures
Vestigial Structures – Structures that are not
necessary for survival
• Evidence of an organism's evolutionary history
• Examples: human tailbone (monkeys)
                snake shoulder and hip bones (lizards)
                whale hip bones (land mammals)
          Genetic Analysis
Comparing DNA of organisms is changing the
  way we view their relationships
• Has produced many surprising results
• Certain species we thought were related are not
related, and vice versa.
   Sharing the same Genes…
Examples: Humans and chimpanzees share 96% of
DNA, humans and mice share 60% of DNA

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