Groundbreaking research over the last 10 years has given rise to the hologenome concept of evolution. This concept posits that the holobiont (host plus all of its associated microorganisms) and its hologenome (sum of the genetic information of the host and its symbiotic microorganisms), acting in concert, function as a unique biological entity and therefore as a level of selection in evolution. All animals and plants harbor abundant and diverse microbiota, including viruses. Often the amount of symbiotic microorganisms and their combined genetic information far exceed that of their host. The microbiota with its microbiome, together with the host genome, can be transmitted from one generation to the next and thus propagate the unique properties of the holobiont. The microbial symbionts and the host interact in a cooperative way that affects the health of the holobiont within its environment. Beneficial microbiota protects against pathogens, provides essential nutrients, catabolizes complex polysaccharides, renders harmful chemicals inert, and contributes to the performance of the immune system. In humans and animals, the microbiota also plays a role in behavior. The sum of these cooperative interactions characterizes the holobiont as a unique biological entity. Genetic variation in the hologenome can be brought about by changes in either the host genome or the microbial population genomes (microbiome). Evolution by cooperation can occur by amplifying existing microbes, gaining novel microbiota and by acquiring microbial and viral genes. Under environmental stress, the microbiome can change more rapidly and in response to more processes than the host organism alone and thus influences the evolution of the holobiont. Prebiotics, probiotics, synbiotics and phage therapy are discussed as applied aspects of the hologenome concept.

These original contributions by symbiosis biologists and evolutionary theorists address the adequacy of the prevailing neo-Darwinian concept of evolution in the light of growing evidence that hereditary symbiosis, supplemented by the gradual accumulation of heritable mutation, results in the origin of new species and morphological novelty. A departure from mainstream biology, the idea of symbiosis—as in the genetic and metabolic interactions of the bacterial communities that became the earliest eukaryotes and eventually evolved into plants and animals—has attracted the attention of a growing number of scientists. These original contributions by symbiosis biologists and evolutionary theorists address the adequacy of the prevailing neo-Darwinian concept of evolution in the light of growing evidence that hereditary symbiosis, supplemented by the gradual accumulation of heritable mutation, results in the origin of new species and morphological novelty. They include reports of current research on the evolutionary consequences of symbiosis, the protracted physical association between organisms of different species. Among the issues considered are individuality and evolution, microbial symbioses, animal­bacterial symbioses, and the importance of symbiosis in cell evolution, ecology, and morphogenesis. Lynn Margulis, Distinguished Professor of Botany at the University of Massachusetts at Amherst, is the modern originator of the symbiotic theory of cell evolution. Once considered heresy, her ideas are now part of the microbiological revolution. Contributors Peter Atsatt, Richard C. Back, David Bermudes, Paola Bonfante-Fasolo, René Fester, Lynda J. Goff, Anne-Marie Grenier, Ricardo Guerrero, Robert H. Haynes, Rosmarie Honegger, Gregory Hinkle, Kwang W. Jeon, Bryce Kendrick, Richard Law, David Lewis, Lynn Margulis, John Maynard Smith, Margaret J. McFall-Ngai, Paul Nardon, Kenneth H. Nealson, Kris Pirozynski, Peter W. Price, Mary Beth Saffo, Jan Sapp, Silvano Scannerini, Werner Schwemmler, Sorin Sonea, Toomas H. Tiivel, Robert K. Trench, Russell Vetter