We do not live alone in nature. Living in an ocean of microorganisms we establish various relations with them; some are parasitic, but most of them are harmless and create symbiotic mutualism. The microorganisms that fix on our body or inside it form the so-called microbiome.The number of microbial cells which establish relationships with our body is 10 times higher than the number of cells built by our own organism. The global genome of the microbiome is about 100 times larger than one’s own genome. These two genomes are associated and form the so-called hologenome, which is especially important for the existence and evolution of the human species. The microorganisms of the microbiome establish their life environment both on and inside our organism – forming somatic ecosystems. In either smaller or larger ecosystems, the microorganisms are interested in the health of the host. As a result of the relationships of symbiotic mutualism, the microbiome took over some functions of the organisms, fulfilling them totally or partially. In such situations, the organism becomes dependent on the microbiome, sometimes to such an extent that it cannot survive in its absence.Along the evolution process, symbiotic mutualism relationships were established between organisms and the microbiome. According to the theory of hologenomic evolution, elaborated by Richard Jefferson , human evolution itself was influenced by the microbiome. The microbiome protects us against the aggression of pathogenous agents and can be used as a weapon against them.