When scientists question facets of existing theories or propose new ones, they present the best evidence available and make the strongest arguments they can to their colleagues. Colleagues in turn challenge that evidence and reasoning. The rigor of this process is what makes science such a powerful tool.
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Lynn Margulis wrote a paper, “The Origin of Mitosing Eukaryotic Cells,” which argued that eukaryotic cells – those with a true nucleus – arose when cells with no nucleus symbiotically incorporated other such cells to make new cells that could perform more functions. The paper was rejected by many journals, and when eventually published by The Journal of Theoretical Biology it was highly criticized. Margulis spent decades defending her work, but scientists now accept her suggested mechanism through which organelles such as mitochondria and chloroplasts evolved. Her suggestions about other organelles have not stood up to experimental tests, and are not as widely accepted.
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In 1982, Stanley Prusiner published an article on his research into scrapie – a disease in sheep related to Creutzfeldt-Jakob disease – which argued that the infectious agent was not a virus but a protein, which Prusiner called a “prion”. Because no one had heard of a protein replicating without a nucleic acid like DNA or RNA, many virologists and scrapie researchers reacted to the article with incredulity. When the media picked up the story, “the personal attacks of the naysayers at times became very vicious,” according to Prusiner. However, his critics failed to find the nucleic acid they were sure existed, and less than two years later, Prusiner’s lab had isolated the protein. Subsequent research provided even more support for prions, and in 1997 Prusiner was awarded the Nobel Prize in Physiology or Medicine.