David Dobbs has a fantastic new article on behavioral genetics at The Atlantic. He adds an important amendment to the vulnerability hypothesis, which holds that certain genes make people more vulnerable to psychiatric disorders. While these snippets of DNA aren’t deterministic per se, when they are combined with traumatic childhood events, or a stressful few months, they can lead to serious mental illness. It’s the old genes plus environment story, and it’s typically cast in a negative light. But Dobbs finds that the vulnerability hypothesis comes with a positive (and often overlooked) flip-side:

At first glance, this idea, which I’ll call the orchid hypothesis, may seem a simple amendment to the vulnerability hypothesis. It merely adds that environment and experience can steer a person up instead of down. Yet it’s actually a completely new way to think about genetics and human behavior. Risk becomes possibility; vulnerability becomes plasticity and responsiveness. It’s one of those simple ideas with big, spreading implications. Gene variants generally considered misfortunes (poor Jim, he got the “bad” gene) can instead now be understood as highly leveraged evolutionary bets, with both high risks and high potential rewards: gambles that help create a diversified-portfolio approach to survival, with selection favoring parents who happen to invest in both dandelions and orchids.

In this view, having both dandelion and orchid kids greatly raises a family’s (and a species’) chance of succeeding, over time and in any given environment. The behavioral diversity provided by these two different types of temperament also supplies precisely what a smart, strong species needs if it is to spread across and dominate a changing world. The many dandelions in a population provide an underlying stability. The less-numerous orchids, meanwhile, may falter in some environments but can excel in those that suit them. And even when they lead troubled early lives, some of the resulting heightened responses to adversity that can be problematic in everyday life–increased novelty-seeking, restlessness of attention, elevated risk-taking, or aggression–can prove advantageous in certain challenging situations: wars, tribal or modern; social strife of many kinds; and migrations to new environments. Together, the steady dandelions and the mercurial orchids offer an adaptive flexibility that neither can provide alone. Together, they open a path to otherwise unreachable individual and collective achievements.

This orchid hypothesis also answers a fundamental evolutionary question that the vulnerability hypothesis cannot. If variants of certain genes create mainly dysfunction and trouble, how have they survived natural selection? Genes so maladaptive should have been selected out. Yet about a quarter of all human beings carry the best-documented gene variant for depression, while more than a fifth carry the variant that Bakermans-Kranenburg studied, which is associated with externalizing, antisocial, and violent behaviors, as well as ADHD, anxiety, and depression. The vulnerability hypothesis can’t account for this. The orchid hypothesis can.

This is a transformative, even startling view of human frailty and strength. For more than a decade, proponents of the vulnerability hypothesis have argued that certain gene variants underlie some of humankind’s most grievous problems: despair, alienation, cruelties both petty and epic. The orchid hypothesis accepts that proposition. But it adds, tantalizingly, that these same troublesome genes play a critical role in our species’ astounding success.

The orchid hypothesis–sometimes called the plasticity hypothesis, the sensitivity hypothesis, or the differential-susceptibility hypothesis–is too new to have been tested widely. Many researchers, even those in behavioral science, know little or nothing of the idea. A few–chiefly those with broad reservations about ever tying specific genes to specific behaviors–express concerns. But as more supporting evidence emerges, the most common reaction to the idea among researchers and clinicians is excitement. A growing number of psychologists, psychiatrists, child-development experts, geneticists, ethologists, and others are beginning to believe that, as Karlen Lyons-Ruth, a developmental psychologist at Harvard Medical School, puts it, “It’s time to take this seriously.”