Answer:
Endosymbiosis is a mutually beneficial relationship between a host organism and an internal associate organism. The term is derived from the prefix "endo," meaning within, and the word symbiosis, which refers to a mutually beneficial relationship between two closely associated organisms.
In her theory of endosymbiosis, Lynn Margulis emphasizes that during the history of life, symbiosis has played a role not just once or twice, but over and over again. Instead of the traditional tree of life branching out from a few common ancestors to many descendent species, Margulis proposes that branches have separated, and then come together again many times as individuals of different species set up symbiotic relationships and formed new organisms. This process formed an interconnected tree of life in which organisms have multiple ancestors, even from different domains. As eukaryotes, our ancestors include both the bacteria that became mitochondria, and the archaebacterium that was the host cell.
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