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19.2: Evolution of Eukaryotes to Multicellular Life

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    5604
  • If you could go back to the late Precambrian, would you recognize these as ancestors of modern life?

    This is a depiction of Dickinsonia costata, a member of the Ediacara fauna. No one knows quite how to categorize these organisms. Some scientists think that they are the ancestors of modern life. But most scientists believe that the Ediacara fauna died out and that other organisms were the ancestors of modern life. If you could go back in time maybe you could figure it out. But since that isn't possible, is there any way to really know?

    Life Gets More Complex

    Eukaryotes evolved about 2 billion years ago. Unlike prokaryotes, eukaryotes have a cell nucleus. They have more structures and are better organized. Organelles within a eukaryote can perform certain functions. Some supply energy; some break down wastes. You can see an example of a eukaryotic cell below (Figure below).

    A eukaryotic cell from an animal

    A eukaryotic cell. This one is from an animal.

    Multicellular Life Originates

    For life to become even more complex, multicellular organisms needed to evolve. Prokaryotes and eukaryotes can be multicellular.

    Toward the end of the Precambrian, the Ediacara fauna evolved (Figure below). The Ediacara fauna was extremely diverse. The organisms appeared after Earth defrosted from a worldwide glaciation. The Ediacara fauna seems to have died out without leaving descendants. Other multicellular organisms appeared in the Phanerozoic.

    A fossil of an Ediacara organism

    A fossil of an Ediacara organism.

    Summary

    • Eukaryotic cells have a nucleus. They also have well-developed structures.
    • Eukaryotes did not evolve until 2 billion years ago.
    • Ediacara organisms probably went extinct. Other organisms were the ancestors to modern life.

    Review

    1. Describe eukaryotic cells.
    2. Why are organelles important to cells?
    3. Describe the Ediacara fauna.

    Explore More

    Use the resource below to answer the questions that follow.

    1. What were the first life forms on Earth?
    2. What is the origin of multicellular organisms?
    3. What three traits are needed for a group of cells to be considered a multicellular life form?
    4. How many branches of complex organisms are there projected to be?
    5. What is the oldest multicellular life fossil found?
    6. What is necessary for all life that we know of?
    7. What do scientists look for when looking for life on Earth?
    8. What needed to happen for cells living in colonies to become multicellular organisms?
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