"The biologist Lynn Margulis, contends that symbiosis is a major driving force behind evolution. She considers Darwin's notion of evolution, driven by competition, as incomplete, and claims evolution is strongly based on co-operation, interaction, and mutual dependence among organisms. According to Margulis and Sagan (1986), 'Life did not take over the globe by combat, but by networking'. As in humans, organisms that cooperate with others of their own or different species can sometimes outcompete those that don't."
Symbiosis - Wikipedia: