Section 1 Change over Time

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Section 1 Change over Time
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Objectives

• Identify two kinds of evidence that show that
  organisms have changed over time.

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• A characteristic that helps an organism survive
  and reproduce in its environment is called an
  adaptation.

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2 kinds of evidence

• Some adaptations are physical, such as fur or
  scales. Other adaptations are behaviors that help
  an organism find food, protect itself, or
  reproduce.

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• Individual organisms that share the same
  characteristics might be members of the same
  species.
• A species is a group of organisms that can mate
  with one another to produce fertile offspring.
• Groups of individuals of the same species living
  in the same place make up a population.

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Do Species Change over Time?

• Since life first appeared, many species have died
  out, and many new species have appeared.

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• Scientists observe that the inherited
  characteristics in populations change over time.
  Scientists think that as populations change over
  time, new species form.

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Objectives

• Explain how comparing organisms can provide
  evidence that they have ancestors in common.

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Comparing Skeletal Structures

• The structure and order of bones of a human arm
  are similar to those of the front limbs of a cat,
  a dolphin, and a bat.
• These similarities suggest that cats, dolphins,
  bats, and humans had a common ancestor.

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Comparing DNA Molecules

• Scientists also compare organisms at the
  molecular level.
• Species that have more DNA in common are more
  closely related and have shared a common ancestor
  more recently.

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• The fact that all existing species have DNA
  supports the theory that all species share a
  common ancestor.

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Section 2

• How Do Population Changes Happen?

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Objective

• Describe the four parts of Charles Darwins
  process of natural selection.

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• Natural selection is the process by which
  organisms that are better adapted to their
  environment survive and reproduce more
  successfully than less well adapted organisms do.

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Darwins Theory of Natural Selection

• In 1859, Darwin published a famous book called On
  the Origin of Species by Means of Natural
  Selection. In his book, Darwin proposed the
  theory that change in populations happens through
  natural selection.

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• Section 3 Natural Selection in Action

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Objectives

• Give two examples of how natural selection can
  result in an adaptation that helps an organism
  survive.

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Changes in Populations

• The theory of natural selection explains how a
  population changes in response to its
  environment. Well-adapted individuals will likely
  survive and reproduce.

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• ExamplesScientists think that hunting in Uganda
  is affecting elephant population. Because ivory
  is very valuable, elephants are hunted for their
  tusks. So, fewer tusked elephants survive to
  reproduce, and more tuskless elephants survive.
  Tuskless elephants pass the tuskless trait to
  their offspring.

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• ExamplesAn insecticide kills all but a few
  insects in a population. The survivors have a
  gene that makes them immune. They pass it to
  their offspring and after a few generations, the
  population is mostly all immune.

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Forming a New Species

• Sometimes, drastic changes that can form a new
  species takes place. A new species may form
  after a group becomes separated from the original
  population. The formation of a new species as a
  result of change over time is called speciation.

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Objectives

• Outline the process of speciation.

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• Speciation often begins when a part of a
  population becomes separated from the rest.
  Populations constantly undergo natural selection.
  After two groups have separated, natural
  selection continues to act on the groups. If the
  environmental conditions for each group differ,
  the groups adaptations will differ.

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• Over generations, two separated groups of a
  population may become very different through
  natural selection due to the division. Even if a
  geological barrier is removed and the groups are
  reunited, they may no longer be able to
  interbreed. If they cannot interbreed, the two
  groups are no longer the same species.