http://en.wikipedia.org/wiki/Symbiogenesis
Symbiogenesis is the merging of two separate organisms to form a single new organism. The idea originated with Konstantin Mereschkowsky in his 1926 book Symbiogenesis and the Origin of Species, which proposed that chloroplasts originate from cyanobacteria captured by a protozoan.[1] Ivan Wallin also supported this concept in his book “Symbionticism and the Origins of Species." He suggested that bacteria might be the cause of the origin of species, and that species creation may occur through endosymbiosis. Today both chloroplasts and mitochondria are believed, by those who ascribe to the endosymbiotic theory, to have such an origin.
In Acquiring Genomes: A Theory of the Origins of Species, biologist Lynn Margulis argued later that symbiogenesis is a primary force in evolution. According to her theory, acquisition and accumulation of random mutations are not sufficient to explain how inherited variations occur; rather, new organelles, bodies, organs, and species arise from symbiogenesis. [2] Whereas the classical interpretation of evolution (the modern evolutionary synthesis) emphasizes competition as the main force behind evolution, Margulis emphasizes cooperation.[3] She argues that bacteria along with other microorganisms helped create the conditions that we require for life, such as oxygen. Margulis believes that these microorganisms make up a major component in Earth’s biomass and that they are the reason current conditions on earth are maintained. She also believes that the DNA in the cytoplasm of animal, plant, fungal and protist cells, rather than resulting from mutations, resulted from genes from bacteria that became organelles. She claimed that bacteria are able to exchange genes more quickly and more easily, and because of this, they are more versatile, which is why life was able to evolve so quickly.[4]
