Cells within cells: An extraordinary claim with extraordinary evidence

Some biologists have come up with a hypothesis that questions the relationship between bacteria and humans. They not only live on you and in you, but you actually carry the descendants of ancient bacteria inside every cell in your body (Understanding Science Team, 2012). They believe that you, technically, are bacteria.

In the 1960s, a microbiologist named Lynn Margulis brought back a hypothesis that dated back from long ago. She, after reviewing evidence from several fields, proposed that several fundamental transitions in evolution occurred, not through competition and speciation, but through cooperation, when distinct cell lineages joined together to become a single organism (Understanding Science Team, 2012). It seemed crazy to many people.
Lynn Margulis studied these topics at the University of Wisconsin. It was here where she studied amoebae under a microscope. She noticed the splitting of the amoebae and the mitochondria. After doing much work with mitochondria, she began to see strange similarities between the organelle and bacteria. She believed that the reason because mitochondria looked and acted so much like bacteria was because they were once bacteria! This ecological relationship between mitochondria and bacteria is called endosymbiosis- one organism living inside another. Her research followed in the footsteps of scientist Gregor Mendel and his work with peas. Margulis also worked on Euglena, a single-celled eukaryote. She found that it had DNA inside its chloroplasts, not just in its nucleus (Understanding Science Team, 2012). While pondering these questions, she remembered the endosymbiotic hypothesis. The endosymbiotic hypothesis has a few “expectations.” The organelles reproduce and are passed from parent to offspring, the organelle has genetic material, their DNA codes for unique traits, and they have close free- living bacteria relatives (Understanding Science Team, 2012). She later displayed this information in her evidence. She remembered that chloroplasts reproduce by splitting in two, as bacteria do and as the mitochondria that she had observed earlier do as well (Understanding Science Team, 2012). She now knew that chloroplasts had their own DNA. With prior information about chloroplasts and now this, was it possible that chloroplasts were once free- living bacteria? She began to explore and work on these new discoveries.
Margulis used many lines of evidence in which she developed to help prove her hypothesis, mitochondria being her example. Margulis proposed that it wasn’t just mitochondria that had evolved from endosymbionts; she thought that plastids and tubule organelles had evolved from endosymbionts as well (Understanding Science Team, 2012). The evidence gained from the mitochondria was relevant to all of the other organelles in at least one category too.
Margulis wrote an article about her discoveries on the endosymbiotic hypothesis. She sent out this article to a few scientific journals, but they all rejected it. It didn’t fit neatly into any single subject areas that theses journals usually covered (Understanding Science Team, 2012). Finally, the Journal of Theoretical Biology accepted it and it was published in 1967. The article sparked a lot of controversy. She won an award from Boston University for best faculty publication of the year. There has much debate on the subject, with new arguments supporting either side. Based on all the available evidence, most biologists reject the hypothesis that tubule organelles descended from endosymbionts. Because of Lynn Margulis, the idea of endosymbiosis became an established part of evolutionary theory.