The stuff we think of when we think about DNA—nose shape, eye color—only comprises about 2 percent of our total DNA. The other 98 percent is called noncoding DNA, and it is responsible for our emotions, personality, and instincts. The epigenome on top of noncoding DNA is very sensitive to stress and the environment. When a body adapts to constant, overwhelming stress—not a car accident or a bad flu, but long-lasting trauma—the epigenome changes. Trauma can turn on a gene that responds to the smell of cherry blossoms, for example. Or turn off a gene that regulates our emotions. It might turn on
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