One Plus One Equals One: Symbiosis and the Evolution of Complex Life

Archibald, a biochemist and molecular biologist at Dalhousie University in Halifax, Nova Scotia, focuses this short and accessible text on “two apparent singularities whose evolutionary significance cannot be overstated.” These two events are responsible for the structure of much of the life on our planet today, and understanding them deepens our comprehension of the evolutionary pathways that have led to the present. The first epic event was the evolution of eukaryotes, complex cells with a distinct nucleus that comprise all multicellular animals and plants. Had this evolutionary step not occurred, Earth would still be populated solely by single-celled organisms. The second was the development of the chloroplast (the organelle responsible for photosynthesis) in early eukaryotes by way of endosymbiosis, in which one cell engulfs and then incorporates the function of another. Archibald recognizes just how momentous these actions were: “What followed was a chain of events that led to a transformation of ocean, land, and atmosphere.” He presents both a clear history of the subject and a concise description of the underlying science. Perhaps most striking is his discussion of the evolutionary implications of endosymbiosis, a process that “acts to bring evolutionarily distinct lineages together in a manner than can lead to the generation of entirely new organisms.” [em](Sept.) [/em]