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The age-old battle between nature vs nurture is something we still haven’t resolved – in particular because the answer is never clearly one or the other, and it always depends on the exact question. While we have learned that brains continue to develop and change after our early years, we haven’t exactly managed to differentiate between how our genes affect these changes in their entirety.

Individual studies on large segments of different teen and child populations have let us better grasp the complexity of how our genes affect brain development, but that development is also heavily impacted by countless environmental factors from financial hardship to peer influence, and the genes we have managed to identify and isolate often control or affect far more than just a single aspect of a teen’s brain and body.

Are Teen Brains Born or Made?

On the most basic level, we can say based on what we have learned that nature vs nurture intertwine and work together to create who we eventually are – and that even after puberty, we continue to learn and evolve in response to the world around us, on the principle of neuroplasticity. Genes play a role in the likelihood of a teen developing in a certain direction. For example, high rates of schizophrenia among a teen’s next of kin would indicate an increased chance of associated symptoms.

But a teen’s environment still plays a significant role in whether these symptoms do or don’t develop, and when. Some factors are protective while others heighten that risk. Some genes are a bit more stubborn. There are markers that help indicate the timing of puberty, which can have an assortment of effects on a teen’s emotional and cognitive development. Environmental factors such as stress and diet still play a role here as well, but just like a teen’s body weight and height, certain physiological aspects are written into our genetic code and are only very minimally affected by our surroundings.

This is also where endocrinology intersects with neurobiology and psychiatry, giving us a little bit of insight into how impossibly complex individual behaviors can be as they’re influenced by a number of internal and external factors. We also have stubborn genes that affect brain development. For example, one trait that was highly heritable was mathematical skill and working memory. Certain anatomical parts of the brain are highly heritable, while others are far more susceptible to environmental impact.

For example, twin methodology studies have proven a genetic link particularly to certain risk factors such as early alcohol use, but that research also indicates environmental factors have a greater influence overall. We cannot predetermine a teen’s behavioral development. Genes might give us some insight on probability and risk, but countless other factors ultimately remain at least equally important if not more so.

Heritability and Environment

We can estimate the heritability of certain traits, behaviors, and mental health issues – but these estimates vary greatly from individual to individual and may not help provide much useful information for parents or laypersons. The heritability of certain traits such as altruism or risk-taking, for example, are estimated to be between 5 percent and 20 percent. That’s anywhere from one in twenty and one in five that an adolescent’s behavior will coincide with their parents.

Researchers can also identify specific genes associated with these behaviors – for example, the gene CADM2 was linked to earlier age at first intercourse, greater number of children, higher number of sexual partners, and more risk-taking behavior. The MSRA gene, in contrast, predicted more neurotic personality traits and later age at first intercourse. In another example, adults with a certain type of FAAH gene had a different brain structure that reduced their likelihood of developing anxiety symptoms after the age of 12.

Research such as this can help us get closer to understanding the interplay between genes and the environment, and provide valuable information to help researchers better analyze public health data – but for individuals, it’s important not to forget that genes cannot ever totally account for a teen’s development, and their influence is limited towards tipping the scales in one direction or another, rather than predetermining behavior.

In response to the need for research clarifying how genetics and environmental factors individually impact the development of certain behaviors, neurodevelopmental conditions, and mental health issues, the NIH launched the Adolescent Brain Cognitive Development (ABCD) study in 2015, a study slated to follow nearly 12,000 children across the country ages 9-10 for a decade. The study is the first of its kind, trying to accurately map behavioral and neurological changes throughout adolescence and early adulthood.

Preliminary results are already offering insight into the development of conduct disorders and antisocial behavior. When taking environmental factors into account, it helps to concretely establish what counts as an environmental factor. While internal factors may include endocrinology and neurobiology, from highly heritable brain anatomy to a teen’s brain volume, external factors include:

    • Stress
    • Diet
    • Trauma
    • Parent relationships
    • Victimization
    • Peer influences
    • Media and advertising
    • Economic distress
    • And more

Some environmental factors are identified as risk factors. Others are identified as protective factors. But it’s more complicated than that. For example, a strained child-parent relationship may be a risk factor for risk-taking behavior and drug use. However, this correlation does not necessarily mean that children who don’t like their parents take drugs as a result. The parent-child strain might be a result of other related factors, ranging from socioeconomic struggles to a history of abuse.

This particular example also brings to light how complicated it can be to trace certain behavior to genes versus environmental factors, as children of addicted parents are more likely to be addicts themselves – not necessarily because of their neurology, but perhaps more so because of their early experiences with addiction and drug use. Whether these factors exacerbate existing neurological issues, cause mental health issues to develop, or simply trigger them and feed them, is up for debate and depends highly on the circumstances surrounding each individual case.

How Nature vs Nurture Both Play a Role in Treatment

Teens develop mental health issues and conduct problems for a wide variety of reasons, and even among teens with one specific condition – such as major depressive disorder – it is impossible to blame a single consistent factor. Genetics and environment go hand-in-hand, both in cause and treatment. A holistic approach is important because the factors that influence behavior and mental health are so complex.

A course of treatment that is purely pharmacological or relies only on therapy might be missing another important contributing factor. Understanding how a teen’s nature vs nurture both contribute to their behavior can help healthcare providers prescribe more accurate and effective treatments.