Lynn Margulis discovered the endosymbiotic theory of the origin of cells. Lynn had an interesting life, aside from being a scientist. She developed the theory of prokaryotic and eukaryotic cells. Many people used her theory in ways they never thought about. Most scientist refused to believe Lynn’s theory about something so obvious and understanding that no one had thought about before. Margulis brought us what we know how the origin of cells came to become. Lynn was a mother of two children and studied in different schools. Lynn was born in Chicago, 1938 she received a bachelor’s degree in the University of Chicago. She later then, married a famous astronomer, Carl Sagan. She then joined the University of Wisconsin, to study biology. She refused to believe the theory of modern evolutionary synthesis which she realized being a ‘neo-Darwin’. Lynn the type of person that didn’t give up, she sticked to her theory and made the world see cells the way she saw them.The major discovery of Lynn was the revolution of prokaryotic and eukaryotic cells. Lynn discovered that it is possible for an organism to live inside another organism. For example, a parasitism inside an animal. Mitochondria and chloroplasts were free-living cells, they were prokaryotic cells but then ended up inside of other cells. It is like a hotel, being comfortable safe place to live, the organelle makes the energy the guests could use. In this theory the mitochondria and chloroplasts come from free-living bacteria species. This discovery was used by everyone, it was a new advance in our technology that no one ever thought about. Organisms can live inside other cells, like chloroplasts and mitochondria. The analysis the mitochondrial DNA, which is passed down from mother to child, and this has helped reveal clues about ancient human migration patterns. The old cells from our ancestors were different than our modern ones. Lynn proved that they went into a change that free-living organisms roamed into other cells. After so much evolution, modern cells are much more advanced and adapted to the cell by the jobs each part of the cells does. Everyone uses it because it has been passed down generation after generation. In conclusion, Lynn’s theory helped revolutionize our modern technology and helped us understand better. She helped the world comprehend how prokaryotic and eukaryotic cells work. No one thought this theory was true, she tried and tried and finally managed to convince everyone that one organism can live inside another organism. Endosymbiotic theory was a major discovery since we all have other organisms inside our cells.