Skin, a Window Into the Evolution of the Human Super-Organism

All life must establish an external barrier that simultaneously interacts with and defends itself from the outside world. Skin is our most important barrier, and human skin has many functions that are in common with other animals but also unique to our species. General skin functions include sensing danger, regulation of internal temperature, maintaining fluid balance and mounting visual sexual displays. Human life also depends on the capacity of our skin to protect us from specific environmental dangers and pathogens unique to us. The central teachings of the medical specialty of Dermatology have been that health is defined by the capacity of skin to perform all these functions while constantly resisting entry of microbial pathogens. However, a recent revolution in understanding skin biology has revealed that normal skin functions are performed not only by cells of human origin, but also by specialized microbes that have co-evolved with us to live in a mutually beneficial relationship. This presentation will provide an overview of the multiple cell types, both human and microbial, that comprise the human skin super-organism. Understanding this relationship changes how we should think about evolution, gene transfer and the impact of current hygiene and antibiotic therapies.