DNA is the command center of cells, but it does not act alone: Our environment plays a major role in the orders that DNA gives to direct how our cells function. We can think of DNA as a piano keyboard and our social and physical environments as the piano players. Surprisingly, DNA seems to be fluid, responding to environmental changes sometimes within as little as 15 minutes, and these changes can be lifelong. So, even though the keys on the DNA keyboard remain the same, the song it plays does not (Feinberg and Fallin 2015; Feil and Fraga 2012). This is especially evident during development. For example, some cells in the developing fetus turn into brain cells, whereas others turn into liver cells. Even though these cells have the same set of DNA, they are responding to different signals that, in total, create all the tissues in the body.
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