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Cooperation goes to the very core of life.

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According to University of Arisona ecologist Judith Bronstein, “every organism on earth is probably involved in at least one and usually several mutualism during its lifetime.”

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Simply put, a mutualism is an interaction that is mutually beneficial.

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If you want to see an example of one at work, just look in a mirror.

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You may be surprised to know that you are a collection of cooperating organisms.

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This may sound odd, but mutualisms are synergistic — they involve different organisms integrating or working together to become something better than the sum of their parts.

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In 1966, Lynn Margulis, a young biology faculty member at Boston University, submitted to a scientific journal a paper proposing that the cells that make up multicellular organisms are collections of cooperating organisms.

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Dubbed the endosymbiotic theory, the idea was not entirely new, having been articulated by Russian biologist Konstantin Mereschkowsky some sixty years earlier.

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But with the benefit of more advanced technology, Margulis was able to develop and defend the idea more rigorously.

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Nevertheless, it was a radical theory with deep implications for the origins of complex life forms.

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The paper, titled “The Origin of Mitosing Eukaryotic Cells,” was rejected.

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Margulis submitted it to another journal.

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It was rejected again.

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And again.

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In all, Margulis recalls the paper being rejected by about fifteen journals before the Journal of Theoretical Biology finally published it.

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Today, the endosymbiotic theory is widely accepted, and Margulis has achieved scientific stardom as much for her tenacity in forwarding the idea as for its veracity.

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Had she been a shrinking violet, we might still be wondering why mitochondria — cellular organelles that are largely responsible for a cell’s energy supply — have their own DNA.

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At some relatively early point in the evolution of life, one unicellular organism engulfed another, both survived, and over the course of another few million years they evolved a mutually beneficial relationship.

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Thus was born the eukaryotic cell, of which all plants and animals are made.

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Multicellular organisms are hives of cooperation.

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In the words of Margulis and her son and coauthor Dorion Sagan: “Life did not take over the globe by combat, but by networking.”