Not long ago in rural Maryland, a mere fifty miles from the bustle of downtown DC, there was a lab in which a scientist and a few hundred rhesus macaque monkeys, over five decades, turned out gobs and gobs of data to decode what, ultimately, makes us who we are. The monkeys are gone now but their legacy lives on in some of the most remarkable science behind genes and mothering, evolution and mental health.
Two things make rhesus macaques particularly suited for the job of studying humans: they share some 95% of our DNA and exhibit personalities just like we do. Steve Suomi was the lab’s last chief scientist until it closed down in 2008. During his time, he saw generation after generation of monkeys whizz through life buffeted by biology and circumstance. Suomi had a special interest in a type of macaques he called up-tight: shy and fearful as infants, they’d grow into something rather similar to depressed human adults. Suomi wanted to know why. Was it nature or nurture? And what did that mean for us humans? Are some of us wired for suffering? Or is it life that twists us one way or another?
Over the past century, our mental deviances have been blamed on rogue genes or unfeeling parents (also known as refrigerator moms), or some combination of the two. The prevailing view in psychiatry — called the diathesis-stress model — holds that some people have an underlying, usually genetic, predisposition to mental illnesses. On its own, though, being prone isn’t enough. Vulnerability tips into disorder once a certain stress threshold has been passed. For illness to ensue, you need a sufficiently harsh environment — a difficult childhood, say, or adversity later in life — to trigger your vulnerability genes.