I Contain Multitudes: ​Short Series offers a new lens on life. With an eye on microbes—microscopic single-celled organisms—larger creatures such as ourselves suddenly look very different. Each of us is more of a society than an individual. Only about half the cells on our bodies are human. The rest make up a menagerie of microbes. Microbes produce chemicals and vitamins that we can’t produce on our own, they help digest food, shape development, and influence behavior.