We tend to separate the brain and the muscle—the brain does the thinking; the muscle does the doing. The brain takes in complex information about the world and makes decisions, and the muscle merely executes. This has also shaped how we think about a single cell; some molecules within cells are seen as 'thinkers' that take in information about the chemical environment and decide what the cell needs to do for survival; separately, other molecules are seen as the 'muscle,' building structures needed for survival.