evolutionary phenomenon, evidence is now overwhelming that obligate or facultative associations among microorganisms and between microorganisms and multicellular hosts had crucial consequences in many landmark events in evolution and in the generation of phenotypic diversity and complex phenotypes able to colonise new environments. Hologenome Development and Evolution Evolution originated from changes in development where variations within species are selected for or against because of the symbionts involved. The Hologenome theory relates to the holobiont and symbionts genome together as a whole. Microbes live everywhere in and on every multicellular organism. Many organisms rely on their symbionts in order to develop properly, this is known as co-development. In cases of co-development the symbionts send signals to their host which determine developmental processes. Co-development is commonly seen in both arthropods and vertebrates. Symbiogenesis One hypothesis for the origin of the nucleus in eukaryotes (plants, animals, fungi, and protists) is that it developed from a symbiogenesis between bacteria and archaea. It is hypothesized that the symbiosis originated when ancient archaea, similar to modern methanogenic archaea, invaded and lived within bacteria similar to modern myxobacteria, eventually forming the early nucleus. This theory is analogous to the accepted theory for the origin of eukaryotic mitochondria and chloroplasts, which are thought to have developed from a similar endosymbiotic relationship between proto-eukaryotes and aerobic bacteria. Evidence for this includes the fact that mitochondria and chloroplasts divide independently of the cell, and that these organelles have their own genome. The biologist Lynn Margulis, famous for her work on endosymbiosis, contended that symbiosis is a major driving force behind evolution. She considered Darwin's notion of evolution, driven by competition, to be incomplete and claimed that evolution is strongly based on co-operation, interaction, and mutual dependence among organisms. According to Margulis and her son Dorion Sagan, "Life did not take over the globe by combat, but by networking." Co-evolutionary relationships Mycorrhizas About 80% of vascular plants worldwide form symbiotic relationships with fungi, in particular in arbuscular mycorrhizas. Pollination Flowering plants and the animals that pollinate them have co-evolved. Many plants that are pollinated by insects (in entomophily), bats, or birds (in ornithophily) have highly specialized flowers modified to promote pollination by a specific pollinator that is correspondingly adapted. The first flowering plants in the fossil record had relatively simple flowers. Adaptive speciation quickly gave rise to many diverse groups of plants, and, at the same time, corresponding speciation occurred in