Symbiosis—Evolution’s Co-Author

Symbiotic integration is a primary contributor to the centerpiece of evolution, genetic novelty. Acquisition of foreign organisms or parts thereof, and potential subsequent assimilation and often internalization of one or several different genomes into another different entity are the foundational expressions upon which natural selection acts, particularly in eukaryotic organisms. Thus, the entire landscape of life-from cells to biomes-is substantially an evolving collection of chimeric communities. Competition may be pronounced and successful in evolution in large part because the competing organisms do not function as, and indeed are not, individuals. Moreover, growing evidence indicates symbiosis to be on a flexible continuum of physiological expression, often with real plasticity in the organisms' integrating life cycles. Therefore, so-called "mutualism", "parasitism", and "commensalism" as symbiotic reference points and analyses may be outdated and perhaps of dubious use. For example, fundamental ecological principles show us that "parasitism" among two different organisms is often of significant advantage to not only the "parasite" but its "host." Symbiosis system examples are here reviewed and redefined on a more meaningful evolutionary context; namely, symbiosis is the acquisition of one organism(s) by another different organism(s), and through subsequent long-term integration, new structures and metabolism emerge.