Each of 100 trillion cells in your body has its own DNA, its own molecular factory for building proteins, and its own biochemical circuitry for making decisions. Though self-contained, these cells depend upon each other, and function together as a unified whole. Some species, such as slime molds, live as independent single-celled organisms in their early life, then unify with other slime mold cells into a multicellular organism for the latter part of their life. Roboticists may one day develop small robots that can similarly assemble themselves into a larger, unified meta-robot.