Ideas About Evolution

1
Ideas About Evolution

• Chapter 6 Section 1
• Pages 154-161

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Early Models of Evolution

• A species is a group of organisms that share
  similar characteristics and can reproduce among
  themselves to produce fertile offspring.
• The characteristics of a species are inherited
  when they pass from parent to offspring. Changes
  in these inherited characteristics over time is
  called evolution.

3
Theory of Acquired Characteristics

• In 1809, Jean Baptiste de Lamarck proposed a
  hypothesis to explain how species change over
  time.
• His hypothesis, called the theory of acquired
  characteristics, suggested that characteristics
  or traits that a parent develops during its
  lifetime can be inherited by offspring.

4
Theory of Acquired Characteristics (continued)

• For example, if a person builds large muscles by
  doing hard work and exercise, this theory stated
  that the large muscles could be passed on to the
  persons offspring.
• Data collected by scientists provided evidence
  that did not support Lamarcks theory.

5
Darwins Model of Evolution

• In December of 1831, a young naturalist named
  Charles Darwin traveled from England to explore
  the coast of South America on a boat called the
  HMS Beagle.
• During his journey, Darwin recorded observations
  about the plants and animals he saw. He was
  amazed by the variety of living things he saw on
  the Galapagos Islands, about 1,000 km off the
  coast of Ecuador.

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Darwins Model of Evolution (continued)

• Darwin hypothesized that the plants and animals
  on the Galapagos Islands must have originally
  come from Central and South America.
• He also noticed, however, that the islands were
  home to many species he had not seen in South
  America. These included giant cactus trees, huge
  land tortoises, and iguanas.

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Darwins Observations

• Darwin observed 13 species of finches on the
  Galapagos Islands, all of which looked similar
  except for differences in body size, beak shape,
  and eating habits.
• All finches also looked similar to a finch
  species Darwin had seen on the coast of South
  America.
• Darwin hypothesized that all 13 Galapagos finches
  evolved from the South American species.

8
Competition and Survival

• Because Galapagos finches lay several eggs every
  few months, Darwin realized that in just a few
  years, just a few pairs of finches could produce
  a very large population.
• A population is made up of all the individuals of
  a species living in the same area.

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Competition and Survival (continued)

• Living organisms produce more offspring than are
  able to survive. Members of a large population
  compete for living space, food, and other
  resources.
• Those individuals that are best able to survive
  are more likely to reproduce and pass on their
  traits to the next generation.

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Competition and Survival (continued)

• Darwin reasoned that Galapagos finches had to
  compete for food. Finches with beak shapes that
  allowed them to eat available food survived
  longer and produced more offspring than finches
  without those beak shapes.
• After many generations, these groups of finches
  became separate species.

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Natural Selection

• After his voyage on the Beagle, Charles Darwin
  returned to England and continued to think about
  his observations.
• He collected more information by studying racing
  pigeons, breeds of dogs, and varieties of flowers.

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Natural Selection (continued)

• In the mid 1800s Darwin developed the theory of
  evolution that is accepted by most scientists
  today, and he described his theory in a book
  called On the Origin of Species.
• After many years and many experiments by other
  scientists, Darwins hypothesis became known as
  the theory of evolution by Natural Selection.

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Natural Selection (continued)

• Natural selection means that organisms with
  traits that are best for their environment are
  more likely to survive and reproduce.
• Their traits are passed to more offspring.
  Although some changes have been made to Darwins
  original ideas, his theory still remains one of
  the most important ideas in the study of life
  science.

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Natural Selection (continued)

• The 5 principles of Natural Selection are
• 1. Organisms produce more offspring than can
  survive.
• 2. Differences, or variations, occur between
  individuals in a species.
• 3. Variations are passed to offspring.

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Natural Selection (continued)

• 4. Some variations are helpful. Individuals
  with helpful variations survive and reproduce
  better than those without these variations.
• 5. Over time, the offspring of individuals
  with helpful variations make up more of a
  population and eventually become a separate
  species.

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Variation and Adaptation

• Darwins theory of natural selection emphasizes
  the differences between individuals in a species-
  these differences are called variations.
• A variation is an inherited trait that makes an
  individual different from other members of its
  species.

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Variation and Adaptation (continued)

• Variations are caused by mutations, or permanent
  changes in the genes of an organism.
• Variations can be small or they can be large,
  such as an albino squirrel in a population of
  grey squirrels.

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Variation and Adaptation (continued)

• If individuals with variations continue to
  survive and reproduce over many generations, a
  new species can evolve.
• This could take hundreds, thousands, or even
  millions of generations.

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Variation and Adaptation (continued)

• Some variations are more helpful than others. An
  adaptation is any variation that makes an
  organism better suited to its environment.
• Variations that are adaptations can include the
  organisms color, shape, behavior, or chemical
  make-up.

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Variation and Adaptation (continued)

• Camouflage is an example of an adaptation because
  it allows an organism to blend into its
  environment.
• This way, it is less likely to be eaten by
  predators and is more likely to survive and
  reproduce. It will then pass its camouflage
  trait to its offspring.

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Changes in the Sources of Genes

• Over time, the changes in the genes of a species
  will cause changes in the appearance of the
  species.
• When individuals of the same species move into or
  out of an area, they might bring in or remove
  genes and variations into a population that
  already exists there.

22
Geographic Isolation

• Sometimes mountains, lakes, or other geographic
  features isolate (separate) a small number of
  individuals from the rest of a population.
• Over several generations, variations that do not
  exist in the larger population might begin to
  become common in the isolated population.
  Mutations can occur to cause these variations.

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Geographic Isolation (continued)

• Over time, the two populations can become so
  different that they no longer can breed with each
  other.
• They have now become separate species.

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The Speed of Evolution

• Scientists do not agree on how quickly evolution
  occurs. Many scientists hypothesize that
  evolution occurs slowly, over tens or hundreds of
  millions of years.
• Other scientists hypothesize that evolution can
  occur quickly. Still other scientists think that
  evidence supports both of these ideas.

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Gradualism

• The model that describes evolution as a slow,
  ongoing process by which one species changes to a
  new species known as gradualism.
• Gradualism says that a continuing series of
  mutations and variations over time will result in
  a new species.

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Gradualism (continued)

• Fossil evidence for some species shows a series
  of intermediate forms that indicate a gradual
  change from the earliest species to todays
  species.

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Punctuated Equilibrium

• Gradualism doesnt explain the evolution of all
  species. For some species, the fossil record
  shows few intermediate forms- one species
  suddenly changes to another.
• This is the model of punctuated equilibrium-
  rapid evolution happens when the mutation of a
  few genes results in the appearance of a new
  species over a relatively short period of time.

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Punctuated Equilibrium Today

• Evolution by punctuated equilibrium can occur
  over a few thousand years and sometimes even
  faster.
• Many bacteria have changed over just a few
  decades.

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Punctuated Equilibrium Today (continued)

• The antibiotic penicillin was first used in 1943,
  and by 1947 a species of bacteria that causes
  pneumonia and other infections had already
  developed resistance to penicillin.
• By the 1990s, several other disease-causing
  bacteria had become resistant to penicillin and
  other antibiotics.

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Punctuated Equilibrium Today (continued)

• When penicillin was used to kill bacteria, some
  bacteria that had a penicillin-resistant
  variation survived, reproduced, and passed this
  resistance on to their offspring.
• Over time, a population of penicillin-resistant
  bacteria evolved.