This may sound fairly high, until you realize that heritability refers only to an underlying risk of depression, not to depression itself. “It’s not Mendelian genetics,” observes Dr. Andres San Martin, a New York City psychopharmacologist. “Causality is a result of interaction,” he asserts, shaped by “multiple factors on multiple levels.”

Probably the most basic error we make is in trying to frame the puzzle of how human character evolves in stark oppositional terms — nature or nurture — rather than seeing it as an inextricable mix of things. Dr. Robert Klitzman, a professor of clinical psychiatry and director of the master’s program in bioethics at Columbia University, observes that “people misunderstand genetics.” “They want to read genetic tests as black and white,” he adds. “Doctors see it much more like predicting the weather.”

Dr. Klitzman points out that people find genes a handy receptacle for blame in what he calls a high-stakes “responsibility game.” We want to know, in other words, if it’s our fault or not our fault — or perhaps our mother’s fault. If it’s your genes, you’re not culpable, and what a relief that is. When Prozac emerged, the biological notion of depression gained traction and the stigma about the disease correspondingly went down. So there are lots of incentives to link psychological disorders to genetic factors, even if it means overstating or blurring reality.

Though science has made rapid advances in the culling of genetic information, it is rare for a common disease to be attributable to one gene; Tay-Sachs, cystic fibrosis and sickle cell anemia are among the few examples. In other instances, even when a gene has been isolated (as is the case with Alzheimer’s), the gene doesn’t begin to account for all cases of those diseases. You can have the mutation and not get the disease, or get it and not have the mutation. It’s all in the intertwining of nature and nurture. Researchers, for example, have reported that the combination of the monoamine oxidase A gene, dubbed “the warrior gene,” and a background of childhood abuse may help explain instances of aggressiveness and antisocial behavior.

Biology is not destiny: a child born of any parent (depressed or not depressed), has about a 16.5 percent (one in six) chance of experiencing a depressive episode during his or her lifetime. Depression is not a single phenomenon, which makes it all the more difficult to figure out the cause.

What’s clear is that for most people, depression appears to be more a result of environment and experience than of one’s inherent nature, which means that “upbringing,” to use an old-fashioned word, still matters. If you do things halfway right and there are no unforeseen traumatic occurrences, like crucial losses or undue stresses, chances are good — better than 50-50 — that the child of a depressed parent will grow up to be a nondepressed adult. That statistic would never persuade me to opt out of the experience of bringing a child of my own into the world. If anything, Zoë has been more of an antidepressant than the best cocktail of meds that I’ve been offered.

Until more compelling genetic information becomes available, it seems that the best we can do is to keep our children’s predispositions in mind while focusing on the pieces of the developmental puzzle over which we can exert control. (This includes being attuned to your child’s nature, especially when it differs from your own.)

Betwixt my lurches into the dark, I gave my daughter a lot of love, which my own parents weren’t capable of doing (a fact I take to be at the root of my own depression, given that neither of them was depressed). These days, Zoë’s no longer the bright-eyed early riser she was as an infant, and she’s got her share of problems, just like the rest of us. But, so far a lifelong case of the blues does not appear to be one of them.