From the late 1960s, Lynn Margulis argued that this view is in any case misguided: that eukaryotic cells did not arise via standard natural selection, but through a series of endosymbioses, in which a number of bacteria cooperated together so closely that some cells physically got inside others. Such ideas trace their roots back to the early twentieth century to Richard Altmann, Konstantin Mereschkowski, George Portier, Ivan Wallin and others, who argued that all complex cells arose through symbioses between simpler cells.
