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Cells within cells: An extraordinary claim with extraordinary evidence


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When biologist Lynn Margulis revived the strange-sounding idea that the merging of cells played a prominent role in the evolution of complex life, the scientific community roundly rejected the notion. Today, this idea is accepted as a textbook fact. Learn more about the evidence and social factors that spurred the acceptance of this key aspect of evolutionary theory.
This article is available from the Understanding Science website.

Understanding Science

Grade level:

30 min

Teaching tips:
Use this resource to relate evolutionary concepts to the topics of organelle structure and function (or get more suggestions for incorporating evolution throughout your biology syllabus). This article can also help students learn about the nature and process of science in the context of science content learning. In-class discussion may enhance student learning based upon this article. Additional student readings are suggested at the end of the article.

Correspondence to the Next Generation Science Standards is indicated in parentheses after each relevant concept. See our conceptual framework for details.

  • Biological evolution accounts for diversity over long periods of time.

  • Through billions of years of evolution, life forms have continued to diversify in a branching pattern, from single-celled ancestors to the diversity of life on Earth today.

  • Present-day species evolved from earlier species; the relatedness of organisms is the result of common ancestry.

  • The early evolutionary process of eukaryotes included the merging of prokaryote cells.

  • Scientific knowledge is open to question and revision as we come up with new ideas and discover new evidence.

  • A hallmark of science is exposing ideas to testing.

  • Scientists test their ideas using multiple lines of evidence.

  • Scientists can test ideas about events and processes long past, very distant, and not directly observable.

  • Scientists may explore many different hypotheses to explain their observations.

  • Science is a human endeavor.

  • Authentic scientific controversy and debate within the community contribute to scientific progress.

  • Our knowledge of the evolution of living things is always being refined as we gather more evidence.

  • Our understanding of life through time is based upon multiple lines of evidence.

Teacher background:

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