All animals coexist in intimate, dependent relationships with microbes. Humans are no exception. Host-associated microbes, like nearly all others on this planet, form communities in which the overall composition, structure, and function are explained by ecological processes and environmental factors. Evidence of coadaptation and mutual benefit are key features of these symbioses between hosts and their microbial communities, or microbiotas.1 The human microbiota is a fundamental component of what it means to be human.
Relman DA. The Human Microbiome and the Future Practice of Medicine. JAMA. 2015;314(11):1127-1128. doi:10.1001/jama.2015.10700