ised for a Monday, turned up three days early, during a Friday evening when I was simultaneously half-watching Monsters, Inc. with my kids and distractedly scanning the messages on my iPhone. At first I didn’t really register what I was reading.

“David,” the message began. “I ran the assay on the DNA from your saliva sample today. The assay ran well and your genotype is S/S. Good thing neither of us think of these things as deterministic or even having a fixed valence. Let me know if you want to talk about your result or genetic issues.”

When I finished reading the message, the house seemed quieter, though it was not. As I looked out the window at our pear tree, its blossoms fallen but its fruit only nubbins, I felt a chill spread through my torso.

I hadn’t thought it would matter.

Yet as I sat absorbing this information, the chill came to seem less the coldness of fear than a shiver of abrupt and inverted self-knowledge—of suddenly knowing with certainty something I had long suspected, and finding that it meant something other than I thought it would. The orchid hypothesis suggested that this particular allele, the rarest and riskiest of the serotonin-transporter gene’s three variants, made me not just more vulnerable but more plastic. And that new way of thinking changed things. I felt no sense that I carried a handicap that would render my efforts futile should I again face deep trouble. In fact, I felt a heightened sense of agency. Anything and everything I did to improve my own environment and experience—every intervention I ran on myself, as it were—would have a magnified effect. In that light, my short/short allele now seems to me less like a trapdoor through which I might fall than like a springboard—slippery and somewhat fragile, perhaps, but a springboard all the same.

I don’t plan to have any of my other key behavioral genes assayed. I don’t plan on having my kids’ genes done, either. What would it tell me? That I shape them in every encounter? I know this. Yet I do like thinking that when I take my son trolling for salmon, or listen to his younger brother’s labyrinthine elaborations of his dreams, or sing “Sweet Betsy of Pike” with my 5-year-old daughter as we drive home from the lake, I’m flipping little switches that can help light them up. I don’t know what all those switches are—and I don’t need to. It’s enough to know that together we can turn them on.

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