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For centuries, the human body was viewed as a self-contained biological entity, functioning independently of the external world. Modern science has profoundly altered this perception. Humans are now recognized as “super-organisms”—complex ecosystems in which human cells and trillions of microorganisms coexist in dynamic symbiosis. The human body harbors approximately 38–40 trillion microbial cells, nearly equaling the number of human cells. These microorganisms—collectively termed the human microbiota— play indispensable roles in physiology, immunity, metabolism, neuroendocrine regulation, and disease susceptibility.