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Key Idea: There are similarities and differences between organisms living today, and between organisms living today and those that lived in the past, both within the same species and between species.

Students are expected to know that:

  1. Although many species have undergone little change for many millions of years, and a few appear to have changed very little since the early history of life, most species living today did not exist when life first began on earth.
  2. Extinctions have occurred throughout the history of life and continue to occur.
  3. Fossils can be used to study the anatomical features of extinct species, and to compare their features with those of existing species.
  4. Fossils include the remains of, or impressions left by, organisms that lived in the past and that have been preserved in rock or gradually replaced by rock.
  5. If available, DNA can be analyzed to learn about species from the past.
  6. Scientists have found similarities and differences among existing species, among extinct species, and between existing and extinct species.
  7. Traits can vary between different species and between organisms of the same species.

Students should be able to:

  1. Read a bar graph that shows variation in a trait within a population.


  1. Students are not expected to know the different kinds of fossils.
  2. Students are not expected to know the fossilization process.