Although the intriguing new documentary Three Identical Strangers, about triplets separated at birth, is best seen without foreknowledge, I think it’s not a big spoiler to say that one of the many questions raised involves the effects of both nature and nurture on human development.

Director Tim Wardle has been quoted about his own conclusions: “Ultimately, this film suggests it’s a balance. You know you are born with certain biological predispositions, but then your environment shapes how those predispositions are expressed. Both nature and nurture, I realize, play a role in how we become the people we are.” (Globe and Mail)

How much of nature and nurture affect mental health conditions? As Erica Hayasaki, The Atlantic, states: “There was a time when scientists tended to think one or the other factor was more important to development, but they have since come to realize how limiting it is to confine our understanding of behavior, health, and identity to this either-or dichotomy.”

A few summaries of current thought follow.

GoodTherapy.org: “Nature, or genetics, has been proven to be an important factor in the development of some mental health conditions, such as schizophrenia, bipolar, and major depression: Bipolar, for example, is four to six times more likely to develop when there is a family history of the condition…”

Addictions is another area in which nature plays a role. “Studies show that alcohol addiction, for example, can recur in families and that certain genes may have an influence over the way alcohol tastes and the way it affects the body.”

And then there are conditions that seem to involve both nature and nurture: “Certain genetic factors may create a predisposition for a particular illness, but the probability that a person develops that illness depends in part on environment (nurture). When a genetic variant indicates the possibility of development of a mental illness, this information can be used to direct positive (nurturing) behavior in such a way that the condition may not develop or may develop with less severity…”

David Rettew, MD, psychiatrist (Psychology Today):

Today, most scientists who carefully examine the ever-expanding research base have come to appreciate that the nature and nurture domains are hopelessly interwoven with one another. Genes have an influence on the environments we experience. At the same time, a person’s environment and experience can directly change the level at which certain genes are expressed (a rapidly evolving area of research called epigenetics), which in turn alters both the physical structure and activity of the brain.

Given this modern understanding, the question of nature versus nurture ceases even to make sense in many ways…

In the end, when the families of children…ask me whether or not their child’s struggles are behavioral or psychological, the best answer I can give them these days is ‘yes.’

Kendra Cherry, VeryWellMind:

Increasingly, people are beginning to realize that asking how much heredity or environment influence a particular trait is not the right approach. The reality is that there is not a simple way to disentangle the multitude of forces that exist. These influences include genetic factors that interact with one another, environmental factors that interact such as social experiences and overall culture, as well as how both hereditary and environmental influences intermingle. Instead, many researchers today are interested in seeing how genes modulate environmental influences and vice versa.